PARASITOLOGY 3.pdf

7/30/2019 PARASITOLOGY 3.pdf

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MEDICAL ENTOMOLOGY

byHenri Lucien Kamga,PhD

Associate ProfessorVice-Dean/RC/FHS

HOD/MLSUBa

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Introduction

Medical entomology is the study ofarthropod in relation to human health.

Arthropods are a group of invertebrateanimals whose bodies are supported byrigid framework of chitinous substancescalled exoskeleton.

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These animals, by nature of their structureand opportunistic habits play major roles inthe transmission of many parasitic andtropical diseases, the knowledge of whichis very essential for a successfulprevention and control of human infection.

The aim of medical entomology is

therefore to control, prevent and if possibleeventually eradicate arthropod relatedhuman diseases.

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CLASSIFICATION OF MEDICALLYIMPORTANT ARTHROPODS

Arthropods of medical importance are thoseones that constitute health hazards or transmithuman infections. They are of 3 main classesnamely: Insecta, Arachnida, and Crustacea.

The class insecta consist of flies, fleas, lice andbugs.

The arachnida consist of the ticks, mites, spidersand scorpions

The crustacean are the crabs and Cyclops.

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Class Arachnida

Members of the Arachnida have bodies divided

into 2 main regions: cephalo-thorax andabdomen. The cephalo-thorax bears four pairsof appendages with no antenna. Members ofthis class include the ticks and the mites.

There are only 2 order of Arachnidae thatcommonly infect man. They are the Acrania or

ticks and the Arcariformes or the mites. Theorder Acrania is subdivided into 2 familiesnamely Argasidae (Soft ticks) and Ixodidae(hard ticks)

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Class Insecta

All members of the class insecta have bodiesdivided into 3 regions: the head, the thorax andthe abdomen. The head bears month partsand a single pair of antenna. There are 2 pairsof wing. The abdomen bears no appendageexcept the terminal circus.

There are 5 orders of medical importance. Thisinclude

Diptera (flies)

Anaplura (lice) Hemiptera (bugs) Siphonaptera (fleas) Dictyoptera (cochroaches)


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Class Crustacea Members of the class have their bodies

divided into head, thorax and abdomenbut the head and thorax are fused intocephalo-thorax a pair of antenna. Theclass crustacean includes the Cyclopsand the crabs.

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MEDICAL IMPORTANCE OF ARTHROPODS The ways in which Arthropods are related to

human health and well-being can be classified in3 divisions as follows:

1- Arthropods as direct agents of diseases ordiscomfort

Entomophobia Exsanguinations Injury to sense organs

Envenomization Dermatosis Myiasis and related infestation Allergy and related conditions

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2- Arthropods as vectors or developmentalhosts

Mechanical carrier (transmission more or lessaccidental)

Obligatory vectors (involving some degree ofdevelopment within the arthropods)

Intermediate host

3- Arthropods as natural enemies of medicallyharmful insects

Competitors

Parasites or predators

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Arthropods transmitted pathogensPathogens transmitted by arthropods are grouped asfollows:

1. Protozoa Vertebrates do not generally acquire strong immunity to

these pathogens, and repeated infection is possible. Entamoeba histolytica: The dysentery amoeba, along with

other intestinal protozoa may be transmitted bycontamination between fecal sources and foodstuffs bycockroaches and houseflies.

Sprorozoa: Plasmodium sp. is a sporozoa, blood parasite

of man transmitted by the Anopheles mosquitoes to manand by many other mosquitoes to other vertebrates.

Trypanosoma: blood flagellates of man, domestic animalsand other vertebrates are transmitted by Ts-ts and bytriatomine bugs, tabanid flies (mechanically) and by flies.

Leishmania: flagellates transmitted by phlebotomine sandflies to man, dogs and other wild animals.

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2. Helminths

Immunity responses in vertebrates areweak and repeated infections are possible.

Insect serves as developmental host oftapeworm, flukes, and roundworms. Fliesand cockroaches may convey helmintheseggs on their body surface or via theirdigestive tract.

Mosquitoes and flies serve as vectors offilarial worms which affect man and othervertebrates.

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3. Bacteria

Vertebrates recovering from arthropodstransmitted bacterial infections develop a strongimmunity.

The majority of common bacteria are transmittedby mechanical contamination; eg: Salmonellaand Shigellatransmitted by houseflies,mechanical transmission of Bacillus antracisbytabanid flies, etc. Bacteria can multiply within avector and be transmitted during the act of foodfeeding.

Rickettsia is a group of very small pathogemicbacteria that are mainly dependent on livingcells for their growth. Rickettsia can betransmitted mechanically by Ixodid ticks after ithad fed on a diseased person.


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4. Viruses

These exceptionally small pathogenic a

gents are made up of a nucleic acid with aprotein coat. Vertebrate recovering frominfections generally develop a strong andlasting immunity. Arthropod act as vectorsof several viruses. Eg: Dengue virus andviral encephalitis, all transmitted bymosquitoes Aedes aegypti.

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Pathogen development in Arthropods

The biological transmission of pathogens is byfar commonest method of pathogen

development among arthropod associateddiseases of vertebrates.

This clearly suggest a long-standingevolutionary partnership between arthropods,which feed on vertebrates and parasiticpathogens that exploit this link or transfer intovertebrates.

This basic classification of these types ofbiological transmission centering on pathogendevelopment is as follows:

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a). Cyclopropagative transmission

The causal organisms undergo differentmultiplications in the body of thearthropod, as in the transmission ofmalaria plasmodia by anophelusmosquitoes.

There are great multiplication in numberwithin the vector, and there are distinct

intermediate growth stages of thepathogens during which it is incapable ofinfecting the vertebrate host.

Only the final growth stage is infective

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b). Cyclodevelopment transmission

In this case, the organisms undergo cyclinalchanges but do not multiply in the body of theArthropod.

The pathogen develops to the vertebratesinfective stage but there is no multiplication innumber.

This type of development is characteristic tohelminthes using arthropods as agent oftransfer: eg: mosquito transmission of filarialworms such as Wuchereria bancrofti, the causalorganism of bancroftian filariasis.

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c). Propagative transmission

The organisms undergo no cyclicalchange but multiply in the body of thevector.

This term is used to describe bacterial andviral multiplication in vectors, for example,the plague organism in fleas, or therelapsing fever organism in ticks.

Any stage of the pathogens can infect avertebrate host;

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Chapter 1: CLASS ARACHNIDA: ORDER

ACRANIA This order is divided into two main groups:

The Ixodid (hard ticks)and the argasid (softticks)

The Ixodid attach for prolonged period to hostsand are therefore familiar to host and aretherefore familiar to most people who have seenthese on themselves.

The Argasid mainly feed for every brief periodand at night. Consequently most people havenever seen these.

The bites of the ticks are characterized byvascular trauma and edematous swelling, andaccumulation of hosts neutrophiles at theattachment site.


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Amblyoma (Hard tick)

Ornithodorus (Soft tick) Prof HL Kamga 20

Once attached, great care should be taken inremoving a tick for the mouth part are easily left

in the flesh as an irritant and source ofsecondary infection.

The length of time a tick remains attacheddepend on the family, the species, whether ornot mating has taken place and the stage ofdevelopment.

Like many Arthropods, both male and femaletick, such blood; great enlargement occurs infemale Ixodid only but in both sexes of Argasid.

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Many disorders on man and animals aretraceable to ticks; among these are:

dermatosis: inflammation, itching, swelling andulceration at the site of the bite, or skinulceration and lesion resulting from improper orpartial removal of ticks mouth-parts.

Exsanguinations, a serious in which a heavilyinfected animal develops anemia.

Otoacariasis, infestation of the auditory canal by

ticks with possible serious secondly infection. Diseases transmitted by ticks including RockyMountain spotted fever and tick-borne relapsingfever.

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High vector potential of ticks

Factors accounting for the potency of ticks in the spread of

diseases of man and animals are the following:

They attach firmly while feeding and do notdetach easily. This contributes in the transfer ofpathogens to the host (especially Ixodid)

Slow feeding: this allows ample time for thetransfer of pathogens to the host (especially

Ixodid) The wide host range in some species insures

more certain sources of blood and opportunitiesto acquire and transmit pathogens.

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The Argasid live every long and this enhances

the chances of acquiring and transmittingpathogen.

Transovarial transmission of some pathogensensures infectivity in some members of thenext generation, a matter of greatestimportance in one-host ticks.

The high sclerotisation of the nymphe andadult make them very resistant toenvironmental stresses.

The reproductive potential of tick is great, assome species may deposit as many as18.000 eggs daily. This helps to enhance thetransmission.

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Life Cycle of ticksAll ticks pass through four stages (egg, lava,nymph, adult) in 6 weeks to 3 years.

Fully engorged females usually deposit theireggs on the ground. The larvae are hexapodand remain in this condition until after the firstmolt.

The nymph emerging from first molt has 4 pairsof legs and remains in this stage untiltransformation to the sexually mature adult.

Ixodid ticks have only one nymphal stage, butthere may be as many as five nymphal molt inArgasids.

The majority of tick species drop off the hostanimals to molt, but in several species moltingtakes place on the host.


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Ixodid ticks have only nymphal stage, but theremay be as many as five nymphal molt inArgadids.

The majority of ticks species drop off the hostanimals to molt, but in several species moltingtakes place on the host.

The longevity and handiness of ticks are very

remarkable and must be considered whencontrol measures are applied, particularlyamong the Argadid which are known to surviveunder starvation conditions for as long as 16years in some species.

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Life Cycle of ticks

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Ticks and Diseases

Disease Pathogen Host Vector

Human ArgasRelapsing fever Spirochaete BacteriumBorrelia recurrentis

Rodent Ornithodorus

Turlareamia Bacterium Francisella tularensis Human Several IxodidsSpotted fever Bacterium Rickettsia rickettsi Human ixodids

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Control of Ticks

Ticks control consists of close observationof host premises and habitat.

Protection against ticks can be achievedby use or repellent which may be appliedto skin, but impregnated clothingparticularly garments provides best

control.

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Chapter 2: CLASS INSECTA ORDERANOPLURA (SUCKING LICE)

This order is subdivided into 3 groups

Crab lice or pubic lice

Head lice

Body lice

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Head louse (left) Crab or pubic louse (right).


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1- Crab Louse: Phthirus pubis The crab louse also called the public louse is

easily recognized by its crabs like appearance. Itinfests the public regions, particularly, but alsothe armpits and more rarely other hairy parts ofthe body, such as mustache, bear and eyeslashes.

These lice are remarkably stationary in theirhabits after remaining attached for days at onepoint with mouthparts.

Crab louse infestation known as phthiriasis ischaracteristic of human adults. Children underthe age of puberty are not usually beingaffected. It is in a sense a venereal disease.

The infection is spread by contact with infestedhumans or objects used by them such asblankets. Prof HL Kamga 32

Head Louse: Pediculus humanus

capitis The Head house is gray in color but tends

to resemble the color of the hair.

Head lice are easily disseminated byphysical contact, particularly amongschool children.

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Body louse: Pediculus humanus corporus

The body louse is more common where theclothing comes in contact with the bodycontinuously, for example on under wears, theforks of the trouser, the armpits, the necks andshoulders.

Suitable temperature is essential for thecontinued existence of louse population and theoptimum temperature for the adult body louse is

approximately the temperature of the normalhuman body.

They do not voluntarily leave unless the bodygrows cold in death or becomes hot with highfever.

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Louse infestation is mainly the result of contactwith lousy persons or their infested clothing.

The presence of lice at any part of the body iscalled pediculosis.

Louse bite may produce certain systemicdisturbances such as general tiredness,irritability, depression, and body rash.

The skin of persons who continuously harborlice becomes hardened and deeply pigmented, acondition designated as vagabonds disease.

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Biology of lice Lice have simple or gradual metamorphosis. The

immatures and adults look similar, except for size.Lice do not have wings or powerful jumping legsso they move about by clinging to hairs with claw-like legs.

Head lice prefer to live on the hair of the headalthough they have been known to wander toother parts of the body. Head lice do not normallylive within rugs, carpet, or school buses.

Body lice live in the seams of clothing, generallywhere it touches the skin, and only contact thebody to feed, usually holding on to the clothingwhile they do this. However, sometimes they willmove to the body itself.

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The eggs of lice are called nits. They are oval whitecylinders (1/16 inch long). The eggs of head lice areusually glued to hairs of the head near the scalp.

The favorite areas for females to glue the eggs are nearthe ears and back of the head. The eggs of body lice arelaid on clothing fibers and occasionally on human bodyhairs.

Under normal conditions the eggs will hatch in seven to 11days. The young lice which escape from the egg mustfeed within 24 hours or they will die.

Newly hatched lice will periodically take blood meals andmolt three times before becoming sexually mature adults.Normally a young louse will mature in 10 to 12 days to anadult (1/8 inch in length). Adults range in color from whiteto brown to dark gray


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Female lice lay six to seven eggs (nits) per dayand may lay a total of 50 to 100 eggs duringtheir life which may last up to 40 days. Adultscan only survive one to two days without a bloodmeal. The nymphs and adults all have piercing-sucking mouthparts which pierce the skin for ablood meal.

The reaction of individuals to louse bites canvary considerably. Persons previouslyunexposed to lice experience little irritation fromtheir first bite.

After a short time individuals may becomesensitized to the bites, and may react with ageneral allergic reaction including reddening ofthe skin, itching, and overall inflammation.

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Crab louse egg (left) body louse egg (right).

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Symptoms of Louse Infestation

Head lice should be suspected when there is

intense itching and scratching of the scalp andthe back of the neck or when there is a knowninfestation in the community.

Close examination of the scalp will reveal small,whitish or dark eggs (nits) firmly attached to hairshafts, especially at the nape of the neck and

above the ears. Inspection may reveal active lice and many

itchy, red marks resulting from irritation causedby the saliva of the louse.

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Although dandruff may resemble eggs, itcan be removed easily from hair, whereaslouse eggs are attached firmly to the hairwith cement secreted by the louse andcannot be removed easily by pulling.

When an infestation becomes known, it isadvisable to examine all members of the

family, especially other children, and otherswho have been in contact with the infestedperson within recent weeks to be sure thatthey have not become infested.

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Body lice are found in tight-fitting sites or seams

of clothing, usually close to the skin. Only inheavy infestations will body lice be seen onother layers of clothing. Infestations usuallyoccur where humans continuously wear severallayers of clothing due to inadequate heating orduring periods of war or natural disasters.

Louse infestations may also occur in poorlymanaged nursing homes, and among the poorand homeless. The main reasons for theseinfestations are the failure to change garmentsand/or poor hygiene.

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Lice and disease

1 Epidemic typhus

Pediculus humanus corporusis probablythe sole agent in the transmission ofRickettsia, the typhus organism, from manto man, although both the head louse andcrab louse can serve as host in which it canmultiply.

The usual route by which man becomesinfected is through fecal contamination. Thebit of the louse is not directly involved:Rickettsiado not occur in the salivary good.


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Louse-borne typhus is a poverty-associated disease. Unsanitary conditions,hot climates with infrequent bathing and

ineffective laundering lead to multiplicationof lice, and consequent opportunities fortransmission.

Typhus is characterized by high fever,backache, bronchial disturbance, andmental confusion. On the 5th to 6th day, ared macular eruption appears on the chestand abdomen, later spreading to the otherparts of the body.

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2. Epidemic relapsing fever

The disease is caused by Borreliarecurrentis. The louse can acquire the

pathogen by a single feeding on aninfected person, but cannot pass it tosecond human in this way.

Man acquires the pathogen by crushingthe louse, usually in the act of scratchingto alleviate the irritation caused by the bite,and in this way releases the spirochete,which then enters the excoriated skin ormucus membrane.

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The incubation period in the human is 3 to 10 days. Theonset of the disease is sudden, with headaches, chillsand fever and generalized pains.

Fever remains high for several days and subsidesabruptly, with an afebrile period of 3 to 10 days followedby one more relapses.

Lice control

Head louse and crab house of humans are all controlledin the same way. Prevention of lousiness isaccomplished mainly by reducing intimate contacts. For

the body louse, control may be achieved by frequentchanges of clothing treating infected garments with hotwater, or fumigation. Lotions containing a persistentinsecticide, or an insecticide with short residual activityplus an ovicide, are highly successful.

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Chapter 3: CLASS INSECTA ORDER SIPHONAPTERA(FLEAS) Fleas are small wingless insects laterally

compressed with long head, compact thorax andrelatively large rounded abdomen. The eyes andantenna are small. Each antenna when not extended lieson the grooves of the sides of the head. Ventrally thehead bears a series of appendages for sensory andfeeding function.

Adult fleas of all species are obligate ectoparasitesof birds or mammals. They are moderately host-specificand their development takes place in the body of theparticular host.

The period of development from egg to pupa isabout 2 weeks depending on the temperature. There are2 larval stages before the pupal stage. They feedregularly on blood, this is the reason why they cantransmit pathogen from host to host.

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Diagrammatic representation of a flea

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Morphology and behavior

Fleas are small, agile, usually dark coloured,

wingless insects with tube-like mouthpartsadapted to feeding on the blood of their hosts.

Their bodies are laterally compressed, (i.e.,flattened side to side) permitting easy movementthrough the hairs (or feathers etc.) on the host'sbody. Their legs are long, the hind pair well

adapted for jumping (vertically up to seveninches (18 cm); horizontally thirteen inches (33cm) - around 200 times their own body length,making the flea the best jumper out of allanimals (in comparison to body size).


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The flea body is hard, polished, andcovered with many hairs and short spinesdirected backward, allowing the flea a

smooth passage through the hairs of itshost.

Its tough body is able to withstand greatpressure, likely an adaptation to survivescratching etc. Even hard squeezingbetween the fingers is normally insufficientto kill the flea; it may be necessary tocrush them between the fingernails or rollthem between the fingers.

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Fleas lay tiny white oval shaped eggs.Their larvae are small and pale with

bristles covering their worm-like body. They are without eyes, and havemouthparts adapted to chewing. While theadult flea's diet consists solely of blood,their larvae feed on various organic matterincluding the feces of mature fleas.

In the pupae phase the larvae areenclosed in a silken, debris coveredcocoon.

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Life cycle and habitat

Fleas are holometabolous insects, going throughthe four life cycle stages of embryo, larva, pupaand imago (adult). The flea life cycle beginswhen the female lays after feeding. Adult fleasmust feed on blood before they can becomecapable of reproduction.

Eggs are laid in batches of up to 20 or so,usually on the host itself, which easily roll ontothe ground. As such, areas where the host restsand sleeps become one of the primary habitatsof eggs and developing fleas. The eggs take

around two days to two weeks to hatch.

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Flea larvae emerge from the eggs to feed on anyavailable organic material such as dead insects, fecesand vegetable matter.

They are blind and avoid sunlight, keeping to dark placeslike sand, cracks and crevices, and bedding. Given anadequate supply of food, larvae should pupate within 1-2weeks. After going through three larval stages they spina silken cocoon.

After another week or two the adult flea is fullydeveloped and ready to emerge from the cocoon. Theymay however remain resting during this period until they

receive a signal that a host is near - vibrations (includingsound), heat and carbon dioxide are all stimuli indicatingthe probable presence of a host. Fleas are known tooverwinter in the larval or pupal stages.

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Micrograph of a flea larva

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Once the flea reaches adulthood its primary goal

is to find blood - adult fleas must feed on bloodin order to reproduce. Adult fleas only havearound a week to find food once they emerge,though they can survive two months to a yearbetween meals.

A flea population is unevenly distributed, with 50percent eggs, 35 percent larvae, 10 percentpupae and 5 percent adults.

Their total life cycle can take as little as twoweeks, but may be lengthened to many monthsif conditions are favourable. Female fleas canlay 500 or more eggs over their life, allowing forphenomenal growth rates.


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Fleas and Diseases

a)- Flea transmits plague to its host in biting by a

mechanical transfer of the bacilli, by its infected

mouthparts, or regurgitation of infected blood.Plague is caused by the bacterium Yersiniapestis, formerly characterized by the epidemicthat has decimated human population of the oldworld.

As soon as the etiologic agent is inoculated, itinitially produces inflammation of the lymphaticgland giving a burbonic type.

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Secondarily there is frequent involvementof blood (giving septicemia type) or thelung (giving the pneumonic type) with

profuse hemorrhage. Plague developsrapidly with a rise of temperature within 2to 3 days. There is headache, the eyes areinjured and the face is characteristic ofextreme illness. There is intensive ratedark coloration of the skin and mucusmembrane in the fatal cases. This is thebasis for the popular designation ofdiseases as the cause of Black Death.

.

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Septicemic plague develops when thebacilli become distributed through the bloodstream. Pneumonic plaque may be theterminal episode of an original burbonicplaque, may be secondary to septicemicplague or may be acquired directly bydroplets spread inoculation from man toman through the respiratory tract.

Plague is managed with drugs such assulfonamides and tetracycline, once thediseases have been contracted. There is avaccine available for immunization

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b)- Tunga penetrans, female is permanentlyadapted to the intracutaenous life on itshost. It regularly infact man, pig and dog.The larvae are free living in dusty andsandly soil.when the adults are also freeliving, the fertilized female find a suitablehost and penetrate in the skin, oftenbetween 8 to 12 days. The infection

begins to irritate so that scratching helpsto expel a large number of white eggs fromthe gigar.

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Flea treatments and control

For humans Flea "dirt" in the fur of a cat is actually excess blood

(from host) consumed by the adult flea, passed as feces.

The itching associated with flea bites can be treated withanti-itch creams, usually antihistaminics orhydrocortisone. Calamine lotion has been shown to lackany effect on itching.

For pets

The fleas, their larvae, or their eggs can be controlledwith insecticides. Lufenuron and fipronil are popularveterinary preparation that attacks the larval flea's abilityto produce chitin. Flea medicines need to be used withcare as many, especially the acetylcholinesteraseinhibitors, also affect mammals. Popular brands includeBayer Advantage, Advantix, and Frontline.

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For the home

Combating a flea infestation in the home takespatience as for every flea found on an animalthere are many more developing in the home.

A spot-on insecticide will kill the fleas on the petand in turn the pet itself will be a roving fleatrapand mop up newly hatched fleas.

The environment ought to be treated with afogger containing an insect growth regulator,such as pyriproxyfen or methoprene to kill eggsand pupae, which are quite resistant againstinsecticides.


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Chapter 4: CLASS INSECTA ORDER HEMIPTERA(TRUE BUGS)

They have piecing and sucking mouthparts. Hemipterausually have four wings folded flat over the body. There isoften a visible triangle at the center of the back that thewing bases do not cover called the scutellum.

The front pair are thickened and leathery at the base withmembranous tips or ends. Mouthparts are formed forpiercing and sucking and the beak arises from the frontpart of the head.

They are found on plants and animals, or in water. Sometrue bugs cause considerable plant damage by theirfeeding. Some are beneficial because they prey on otherinsects. A few bite humans on occasion.

Metamorphosis is gradual, with immatures usually quitelike the adults but wingless. Most are under 1/2-inch longbut some forms especially aquatic ones may be over 2inches long

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They are also found on crevices of walls, ceiling, foamsand furniture during the day. They come out to feed atnight. They bits are characterized by severe and prolongitching and inflammation may result in secondary

infection. Bite may also cause general allergic symptomssuch as blurred vision, heart palpitation, headache andfever.

Identifying characteristics for the order Hemipterainclude:

Front wings generally hemelytrous, i.e., thickened at thebase and membranous at the tip.

Hind wings membranous and shorter than the frontwings.

Antennae with 5 or fewer segments. Mouth with a 3- or 4-segmented beak arising from the

front of the head.

Tarsi with 3 or fewer segments.

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Photography of a Bug

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Bugs and diseases

Bed bug has been experimentally incriminated ascarrier of relapsing fever, plague, typhoid fever,kalaazer, epidemic typhus, but there is no directevidence to show that they transmit these infections toman under natural conditions.

Two species attack man: Cimex lectularisand Cimexhemipterus

Reducviid bug, kissing bug and assassin bug areagents of chagas diseases. Trypanosoma cruzimultiples in the mid-gut and the arthropod may remaininfective for about 2 years.

One of the methods to diagnose chagas disease is toallow clean uninfected laboratory-bread reduviid bugto feed on suspected patient. This method is calledXenodiagnosis.

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Chapter 5: CLASS INSECTA ORDER

DIPTERA (True Flies) Diptera are 2 wings insects. All the wingmembers have only one paire of wings.Instead of a second posterior paire, there is apaire of short knobbed structure called haptereused in balancing the body. This order isdivided into 3

Sub-order Nematoara subdivided into 5families

Culicidae true mosquitoes Simulidae black flies

Psychodidae sand flies Ceratopogonidae biting midges Chronomidae non biting midges

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Sub order Brachysera. With only one

medically important family Tabanidae ex:Chrysops.

Sub-order cyclorrhapda or muscoid fliessubdivided into 6 families

Chloropdae or eye gnat

Muscidae or house flies

Glossinidae Tse-tse flies

Callophoridae blow flies

Sarcophagidae sarcophages

Hypoboscidae house flies


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1 Sub-order Nematocera

1.1 True mosquitoes

They have conspicuous proboscis and are importanttransmitting agents of viral, protozoan and helmintic

diseases of man and animals. They can be distinguishedfrom other diptera by

Elongated mouth parts of the female adapted for piecingand sucking blood

The long antenna

The wing venation is characteristic with flat striatedscales on the longitudinal veins and the posteriorborder.

The body is divided in 3 main regions; the head whichbears the eyes, the antenna and the mouth parts, thethorax to which the wings and legs are attached, and theabdomen bears the external genitalia.

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1.1.1 Habits and habitats of mosquitoes

Mosquitoes are found throughout the world.Some species are essentially rural are, othersare urban and domesticated. Still other arefound only in the jungle and forest.

All types of fresh water, marsh or polluted waterprovide breeding ground. Poorly drained or

transiently inundated (temporary flooded) landsupport heavy population of mosquitoes.

Favourable temperature, ample food supply forlarvae and adult and protected breeding groundprovide an abundance of mosquitoes.

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Homeothermal animals including man arethe sources of blood for female mosquitoes.

Some species are anthropophilic that is theyprefer humans for food, while others areessentially zoophilic. Most mosquitoes areendophagic when they obtain their bloodmeal within man shelter and other areexophagic when they suck their blood mealout doors.

Mosquitoes have been classified asendophilic when they remain inside man-made shelter and as exophilic, they spend agreater part of their genethrophic cycle out ofdoors.

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As a rule a pregnant female mosquito cantproduce fertile eggs without taking blood.

Most anopheles mosquitoes are aggressivebiters by twi-light but stay inactive in brightdaylight.

The time of digestion of blood meal varieswith the species of mosquitoes and also thetemperature. Longer time is required in coldweather than warm weather.

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1.1.2 Life cycle of mosquitoes

Mosquitoes undergo completemetamorphosis.

The eggs produce voracious rapidlygrowing larvae that mold 4 times beforethey enter the non-feeding pupal stage fromwhich the fully developed insect emerges.

The length of time required from ovipositionto adult varies from 2 weeks to 6 monthsdepending on food supply and temperature.

Moisture is necessary for the hatching ofthe eggs.


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The hatching time of the egg varies widelyand the eggs of different species vary intheir ability to withstand high and low

temperatures. The larva breaks out of the anterior end of

egg by using a sharp projection of hishead.

The pupa has the form of a question markand the emergence of the adult oftentakes place at night when water is calm.The non-breeding stage lasts for about 4to 5 days.

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Life cycle of a mosquito

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1.1.3 Mosquitoes as vectors of diseases

Mosquitoes serve as cyclical or mechanicalvectors of 4 types of organisms pathogenic toman.

Protozoa:Mosquitoes serve as vectors ofplasmodium, causative agent of human malaria.In some areas of the world there are cases ofmosquitoes without malaria. This phenomenonis explained on the basis of Lack of suitable vectors

Vector density below a critical level sufficient tomaintain the disease

Climatic condition infavourable to the development ofmosquitoes.

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In certain areas however, 4 factors are importantin the maintenance of the disease.

Those that determine the stability of thediseases (mosquito longevity mosquito bitinghabit, the mosquito cycle of the malaria parasite

Those that determine the initial transmission (egmosquito density

Those which determine the normal season oftransmission (eg: climatic factors)

The inoculation rate (how many sporozoites themosquito infects in the human) and the state ofcommunal immunity.

Prof HL Kamga 77

It is recognized that malaria occurs in relatively

stable and unstable conditions. In stable malaria, there is high rate oftransmission to the affected population, nomarked fluctuation occurs over the year, and ahigh collective immunity of the population makesepidemic unlikely.

In unstable malaria, there is a markedseasonal or other fluctuation, and immunity ofthe population is often low.

If there is some measurable incidence of thedisease continuously present in a given area,the disease is said to be endemic and variousdegree of endemicity are recognized by theprefixes hyper hypo-holo.

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Filariasis:Filarisis is an infection of man by filarialnematodes, and mosquitoes are the vectors of 2of those nematodes

Wuchereria bancrofti Brugia malayi

The development of both follow similar feature.The microorganism develops in the peripheralblood during feeding.

The development of microfilaria takes place inthe thoraxic muscles of the mosquito from wherethey migrate toward the stomach.


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They undergo 2 molds before reaching theinfective stage, they can then migrate toproboscis of mosquito from where they

enter the definitive host during themosquito blood meal.

Infective larva enters the vertebrates hostand develops into mature parasites. Theyproduce microfilaria in the peripheralblood. In obstructive filarisis(elephantiasis) there is gross enlargementof structures (scortum, brest and legs) dueto blockage of lump drenage as aconsequence of many years of exposure.

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The microfilarias are particularly prevalent in theperipheral blood at night: they are periodic.

The selective factor which dictate the periodictity

is the response to the vector with the incidenceof peripheral blood, microfilaria coinciding withthe natural biting period of the local vectors.

The periodic form with marked nocturnalperiodicity is characteristic of humid tropics andis transmitted by night biting mosquitoes (eg:Culex fastigans).

Bancroftian filariasis is largely an urban and sub-urban disease due to the habit of the principalvector (culex) while Brugian filariasis is apredominant disease of the far-East where itstransmitted by Mansonia mosquito

Prof HL Kamga 81

Yellow fever:Yellow fever is a disease of high mortality inadult and is transmitted by the domestic mosquito Aedesaegyptiwhich breads in water tanks and containers nearhouses. The mosquito can only be infected by biting apatient during the first 3 days of the disease. The virusrequires an incubation period of 11 days to becomeinfective. Aedes africanusand Aedes simpsoniare alsoimportant natural hosts but Aedes aegyptiis the vector ofthe epidemic disease.

Dengue:Dengue is an endemic viral disease of low fataitycharacterized by abrupt onset, fever, rash, intramuscularand joint pains and marked hemorrhagic complication canalso occur. The vector mosquito is Aedes egypti. The

mosquito can acquire the infection up to 3 days after theinitial symptoms, transmit it after being infected for about 7days and may remain infectious for life.

Viral encephalitis: This disease is transmitted by culinemosquito. There are various forms of viral encephalitis butonly about 1% show clinical symptoms like fever, vomitingrigidity and mental confusion.

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Typical Anopheles mosquitoes Aedes mosquitoes

Typical illustration of culex moscutoes (left) taking blood meal (right)

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1.1.4 Mosquito control

The control of mosquito involves the knowledge of thehabit of the particular species, the topography and theclimate of the areas, racial and economic status of thepopulation. Mosquitoes may be controlled in several ways.

Elimination or reduction of breeding ground can be done inthe following ways

i)Local measures of Emptying containers of stagnant water

Filling of depression and pools Screening of cisterns and others bodies of water that can

be drainedii) Alternation of water level, flushing of streams which

periodically alters the water levels as well as agitating thewater

iii) Removal of vegetation from bank and water surfaces andexposing water to wave action inhibit the breeding ofmosquitoes.

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Destruction of mosquito larvae using

i)Natural enemies (eg: fish gambusia)ii) Poison (larvicide) eg: oil Measures directed against the adult mosquito

destroyed by trapping and screening of windowsand doors using insecticides

i)For the immediate killing of adult mosquitoii) For the residual killing of mosquito Protection against mosquito by building light airy

rooms in which mosquitoes attack less readilythan the dark rooms.

In mosquito infested area the individual will beprotected by applying mosquito repellents theskin and any other exposed parts of the body.


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1.2 Family Simulidae or black flies eg:Similium damnosum

Characteristics:

These flies are stout and small

The mouth parts include blade and littlestyle in the female used for peering

The eyes are separated in the females butcontinuous above the antenna in males

They are usually found in areas of swiftflowing streams. They are nearly alwaysfound in water, shallow mountain torrentbeing the favoured breeding places.

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Black fly (Simulium damnosum)

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The larvae attach themselves to rocks or othersolid materials in the steam. Nectar from flowersprovides a very good support for male, butfemale usually require blood meal for ovariandevelopment.

As in other Nematocera the male never sucksblood. Larval food consists of small suspendedcrustacean, protozoa, algae and plants. Thereare about 6-7 larval stages. Pupation takes

place in basket like cocoon. Cold weather retards the emergence of theadults. Simulies are daytime biters and arerarely found indoors.

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Black flies and disease The most important human parasitic disease

transmitted by Simulium flies in Onchocerciasis

or river blinders causes by the filarial wormOnchocerca vulvulus.

Both sexes occur in the subcutaneous nodulesjust under the skin and they are found mostly onthe lower parts of the body.

Deep nodules or bundles of worms may alsooccur against the joints, between the musclesand against the periostum of bone where theygive rise to deep pain or rather they cause deepabscesses.

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The microfilaria produced viviparously by

the female worms migrate to the skin fromwhere they are picked up by the Simuliumfly during the blood meal.

They then migrate to the thoracic muscleof the fly where further development takesplace. They then migrate to the vectorshead and proboses from where they aretransferred to the host during the flysblood meal.

Reproduction and multiplication of theworms occurs only in the vertebrate host.

Prof HL Kamga 90

In man, prolonged and repetitive exposure

to infection by fly biting will progressivelybuild up parasitemia.

Only the Sarcophagia and not the adultworm produce important pathology in man;the lymph gland may be swollen and aform of elephantiasis may occur. Serioussystemic involvement of lung and livermay develop.


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The most important effect is the blindnessresulting from microfilaria migration from

the nodule through the skin of the face andthe conjunctive to the eyes.

Though massive involvement is needed toproduce blindness, impaired vision mayoccur in up to 50% of the population.

It requires a lot of worm to causeblindness.

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Family ceratopogonidae or biting midges

They are very small slender gnats. Theirbiting habits resemble those of simulidflies. They are anthropophagic and oftenmistaken for simulid.

Only the females suck blood. Some ofthem are autogenic, although the femalessuck blood.

Culicoides furensis vicious biter andhas been known to be involved in thetransfer of pathogemic nemathods,protozoa and viruses

Prof HL Kamga 93 Prof HL Kamga 94

The night-biting Culicoides austeniis theintermedia host of Dipetalonema pestans.The microfilaria of D.pestansare found inthe peripheral circulation both by day andnight.

The microfilaria undergo metamorphosis inthe body of the fly and they appear on theproboses.

Culicoides grahamiis anotherintermediate host of D. streptocercaandMansonella ozzardito man.

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Family psychodida or sandfly. Genus:

Phlebotomus The adults are small, with conspicuous blackeyes, heavy body, wings and legs. The ovallanceolate wings are carried erect.

The male and the unfed female can readily passthrough the mosquito net, but fully engorgedfemale is too large to pass through. Only thefemale feed on blood.

Feeding occurs at right when there is little or nowind. Typical breeding places are indoor stores,cracks poultries, houses, and other situationscombining darkness, humidity and the supply oforganic matters which serve as food for thelarvae.

The bleeding place is never aquaticProf HL Kamga 96


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The long ovoid eggs are laid in batches ofabout 50 in cracks and crevices in darksmoist areas. The larvae feed on organic

matters like excrements of lizards andrats. After 4 laval stages and the neckedpupal stage, the adult emerges after 30 to40 days.

Most species of Phlebotomusare foundin the warmer climates in the world andare noted for the transmission of sand flyfever the pathogen of Leishmaniasis andother viral infectious diseases.

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Sand-flies and diseases

Sand-fly fever is an acute infection characterized

by fever and severe headache. It is caused by

an arbovirus and develops after rain. Only thefemale transmits the infection.

Sand fly feed at daylight time, usually at groundlevel but rarely higher.

Leishmaniasis are caused by parasitic protozoa

which develop in the digestive tract of the insect.The disease is classified as visceralLeishmaniasis or Kala-azar and cutaneousLeishmaniasis.

Prof HL Kamga 99

Kalaazar is a tropical spenomegalic diseasecause by Leishmania donovoni.

In man there is a progressive enlargement,the spleen and later of the liver.

As the disease progresses the skin becomegreenish.

Non-treatment leads to fatality. After some

few weeks the conditions is still acute, butafter 2 days, it evaluates to a chronic case.

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Cutaneous leishmaniasis is a chronic diseaseknown by various names: espundia, cuteneousleishmaniasis, chicklero ulcer.

Leishmania is widely distributed in the tropicsbut the most serious cases are found inAmerica.

Espundia involves the nasopharyngeal region

and may result in horrible disfiguring ulcer thatmay destroy the nasal cartilage and born.

The most pathogenic is Leishmania braziliensis.A number of animals serve as reservoir of theinfection eg: the rat.

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Sub-order Brachysera

Family Tabanidae or horse flies

They are large blood sucking flies known bythe variety of names: horse flies, deer flies,mango flies or mangrove flies. They are heavybodies and strong flyers. Only female bite andsuck blood. Their eyes are very large and widely

separated (dichroptic) in females. Males eyesare usually holoptic and together. The wingvenation is characteristic. The mouthparts of thefemale are blade-like and function as cuttinginstruments, though it is fitted for sponging.

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The breeding habit of most species isaquatic or semi aquatic. The eggs aredeposited in layers on objects in slow

water, or situation favorable to the larvae,eg: overhanging vegetation, projectingrocks and sticks and emerging aquaticvegetation.

The larvae have a slender cylindralcontractile body consisting of small headand 12 additional segments. The puparesembles that of the butterfly. The adultfly emerges from the pupa case.

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Biological adaptation for transmissionof pathogen

Anautogeny or requirement of blood meal forthe maturation of eggs stimulates the host-sucking tabanid, to which transfer of pathogenfrom a carrier to the host is accidental

Telmophagy or pool feeding is a rule.

Microorganism from the lacerated superficialtissues and peripheral blood are drawn intothe pool from which the fly such blood.

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Tabanid take relatively large blood mealwhich consequently can contain a largenumber of pathogens.

Some species have a relatively engorgementtime which permit adequate contact for thetransfer of the pathogen

Because of the intermittent feeding of Tabanidthe likelihood of their being involved in the

mechanical transmission, sick and healthyindividuals may be attacked in succession bythe same fly.

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Horse flies and Disease

Loa loa is an African worm that occurs inthe tropical belt.

The adult is found in the superficialsubcutaneous connective tissue. Microfilaria ofLoa loaare found in the peripheral blood fluideither at a diurnal or nocturnal periodicity.

They are infected by Tabanid of the genuschrysops where they undergo development inthe thoracic muscle.

Metamorphosis is completed in 10 12 daysand when the infected fly bits, the matureinfective larva from the proboscis of the insectenters the skin of the host.

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Sub-order cyclorphapha or Muscoid

flies (non-biting flies)

This group includes 6 families, viz:

Chlorpidae or eye flies

Muscoidae or house flies

Glossinidae or Tse-Tse flies

Collophoridae or blow-flies

Sarcophagidae or arcophagi

Hypoboscidae or house flies

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All the cyclorrhapha have the followingcharacteristics

i) A pair of large compound eyes separatedfrom each other in the female

ii) An individual flagellum

iii) The typical larvae is a maggot with thefollowing characteristics

Legless

More or less cylindrical

Distinctively segmented

iv) They all have a complete metamorphosis


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Family Chloropidae

They are very small

They are attracted by sebaceous secretions,pus, blood, exposed genital organs of mammals

They do not bite

They cause myasis

Medical importance of chloropidae

Their habit of freely visiting sources ofcontamination readily predisposes them to

mechanical transmission. They are suspected tobe the transmitters of the organism causingbacterial conjunctivitis as well as organismresponsible of the bacterial yaws.

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Family Glossinidea

Tsetse flies are large, yellow-brown or brown-blackand measure 6-15m in length. They are

distinguished by a rigid projecting proboscis and along pair of accompanying palps. There is

a characteristic axe-shaped venation of the wingswhen viewed dorsally resembling an

inverted hatchet in the central cell. The antennaeappear short and feathery, and the abdomen

is segmented and often striped or patched. Bothmales and females suck blood every 4-5

days, outside in open spaces.

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Female Tsetse flies are unique in the sense thatthey deposit larvae and do not lay eggs.

The eggs mature within the female and aresupplied with essential nourishment to completelarval development.

This cycle requires a large number of blood mealsto maintain and thus the female requires regularfeeding. The larvae are normally deposited inshaded areas.

There are three larval instars with the mature

larva appearing white, visibly segmented with apair of lobes at the posterior end.

Pupation of the third instar results in a darkcolored puparium with posterior lobes. The pupalperiod is extended (3-7 weeks) depending on thesurrounding environmental conditions.

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Tsetse flies are vectors for Africansleeping sickness (Trypanosoma bruceisp.)

The two subspecies of T. bruceithat infectMan are morphologically identical. T. b.gambiensecauses Gambian sleepingsickness in Western Africa and T. b.

rhodesiensecauses Rhodesian sleepingsickness in East Africa. Anothersubspecies, T. b. brucei, causes nagana incattle.

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Initially the patient has a headache, fever, chills

and loss of appetite but specific clinical signs areabsent. Parasitaemia comes in characteristicwaves. Later, the spleen, liver and lymph nodesenlarge (Winterbottom's sign).

Finally, there may be CNS involvement leadingto coma and death within several years.

Trypanosoma brucei rhodesiense(rural EastAfrica): this is so acute that the patient invariablydies before classical symptoms develop.

Without appropriate treatment, both forms arefatal.

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Family Muscoidea

Many of them are found indoors and are actual orpotential menaces of human health. They habituallyenter the house, come in contact with human food afterbreeding and feeding on excrement, death animals andother contaminated media. Those flies that have enteredthe man dominated ecological community andconsequently coexist with man over an extended periodof time are called Synanlthropic species.

Various degree of synanlthropy exist from the totalassociated with man to quite a loose and facultativeassociation. Total association involves completedependence on the man-controlled environmentincluding his households food for the completedevelopment.

The main medical significance of synanlthropy lies inits potential hygienic implication and the individualrequirement of the fly. The classification of synanlthropyis highly significant medically.


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Tse-tse fly

Domestic flyProf HL Kamga 116

Life Cycle of the Domestic fly

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Flies and Diseases

Buzzing flies may have a serious impact onindividuals mental health, and some personshave pathological fear of flies. Generally anoisily buzzing blowfly within the house doesnot lead to mental well being.

Flies as germ carries

Houseflies are a danger to the health of manand animals principally because it carries andspreads disease organisms. They move from

garbage and sewage to our dinner plates. Itcarries bacteria on the outside of its body, itregurgitates saliva and deposits wastes onhuman food. By comparison the cockroach issanitary

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The house fly, by the nature of its structure and

opportunistic habit is an important pathogen-transmitting insect:

It is an eusynanlthrope over most of its life. Itfreely enters houses and area where personsaggregate, as well as restaurants, stores andother places where human food is available, and

it freely leave houses to frequent human andanimal excrements.

If feeds on human food and animal excrementsalike. Because this fly can only take liquid food,it constantly vomits for the purpose of liquefyingsolid materials. In this deeding process, droplets

of excrements are constantly deposited.

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Structurally the fly is well adapted for picking up

pathogens. Its proboscis is lined with a provisionof fine hairs and pseudo-tracheal channels thatreadily collect contam

inants.

The foot of the fly presents a complexity ofstructure. Each of the 6 feet is fitted with heavystructures and parts that secrete a stickingmaterial that adds to its collecting abilities.

These habits and structure result in aremarkably effective mechanism, for mechanicaltransmission of any pathogen, small enough tobe carried, particularly microorganism andhelminthes.

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Diseases transmitted by house flies

1. Bacteria i) Bacterial enteric disease:housefly is

involved in the transmission of the pathogenicenterobacteriacea. The bacteria involved belongto 3 genera

Species of Shigella: important agents ofbacterial dysentery and shigellosis man and canbe transmitted through food, water and milk.

Salmonella, the agent responsible of typhoidfever and other salmonellosis,

Pathogenic Serotype of E.Coli: often associatedwith infant diarrhea and travelers disease inadults.


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ii) Cholera:House flies have been incriminated as vectors ofVibrio cholerae, the causative agent of cholera, because, in1886 this organism were found in flies caught. Subsequentisolation from flies and their feces, together withepidemiological evidence, confirmed that flies play importantroles in transmitting the pathogen from human feces touninfected individuals in endemic areas where water is notthe major vehicle.

iii) Yaws:This disease is caused by a spirocheteTreponema Pertenuewidely distributed in the tropics. Thepathogen is found in superficial ulcers in the hands, feet,face and other parts of the body. Presence of the Yawsorganism has been demonstrated in the mouthparts and legsof flies that has been feeding on ulcers of yaw patients.

iv) Tuberculosis:Although flies have been incriminated inthe transmission of Mycobacterium tuberculosis, noconclusive evidence have shown that that flies can transmitthis organism in natural condition, though flies have beenobserved to feed on human sputum, and infectivemycobacteria have been found in their feces.

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2. Poliomyelitis and other enteroviralinfection

Although non-biting and billing flies, aswell as mosquitoes have been suspectedas vectors of the polio virus, the greatestsuspicion now rest on flies that feed andbred on excrement and garbage. A seriesof evidence suggest that houseflies canharbor the polio virus and under certaincircumstances can transmit it either byexternal contamination or by internalpassage following feeding on human food.

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3. Parasitic diseases

Intestinal protozoa

Entamoeba histolyhtica, the most frequent cause ofamoebic dysentery in man and Giadia lambliathe agentof giardiasis have both been isolated from flies takenfrom around food destined for human consumption.

Flies involvement assumes great importance in areaswhere unsanitary conditions prevail. The pathogen mayalso be transferred from feces to host by carelesshandling of food or contaminated water.

Eggs of parasitic worms:Extensive work has

confirmed the dispersal of eggs of parasitic worms byhouseflies.

The list includes eggs of Taeniaspecies and nematodesspecies. The ability of houseflies to transmit thesehelminthes is unquestionable.

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Chapter 6: MYASIS

Myasis are defined as the invasion of livingtissues of man and other animals by dipterial

larvae.

Myasis producing flies belong to 4 families:

Ostridae

Sarcophagidae

Calliphoridae

Muscidae

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Classficiation of myasis

Myasis is clinically classified as Cutaneous myasis when the larvae live in or under

the skin

Intestinal myasis when the larvae are present inthe stomach or/and the intestine.

Atial myasis when the larvae I made the oral,nasal, ocular, sinual, vaginal and urethral cavities;all these are natural openings.

Wound myasis: when the larvae invade artificiallesions.

Myasis can also be grouped according totheir oviposition or larviposition habit into 3classes.

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Specific myasis

The diptera deposit their eggs or larva in or near living

tissues and the larva inevitably become parasite. This groupmay be subdivided into:- Flies that deposit their eggs or larvae in the habitat of thehost (bed, chair, etc)- Flies that deposit their eggs or larvae on the bobby of thehost.- Flies that deposit their eggs or larvae in wound anddiseased tissues.

Semi-Specific myasis

Semi-specific myasis flies usually deposit their eggs orlarvae in the flesh or vegetable matters and less frequently indiseased tissues and neglected wounds. Large number oflarvae so deposited often cause extensive tissue destruction.

Accidental myasis

Accidental myasis producing flies usually deposit their eggsor larvae in excrement or decay, organic matter andsometimes in food. Their larvae produce intestinal or urinarymyasis.


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Family genera Type of myasis LocationDermatobia Specific Cutaneous

Atrial

InternalGasterophilus Specific

CutaneousHypoderma Specific Cutaneous

Oestris Specific Atrial

Ostridea

Rhinoestris Specific AtrialCalliphora Non specific Wound

Cutaneous

AtrialCalliboga Specific

Wound

Cordylobia Specific Cutaneous

Lucilia Specific Wound

Calliphoridae

Phormia Specific WoundAtrial

CutenaousSarcophagidae Sarcophagi Specific

Wound

Myasis-producing flies important in human andveterinary medicine fall into 3 main families

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Common Myasis1- Intestinal Myasis

Intestinal myasis is largely accidental in manalthough 30 species of dipterous larvae have been

found in gastro intestinal tract. These accidentalinvaders are from flies that breed on decay andorganic matter such as Fannia canicularisandEristalis tenax.

The intestine is the normal environment of theparasitic gasterophilus larvae. The larva of the fleshfly Sarcophagamay gain entrance through the anuswhen the eggs are deposited in the anal orfice ofinfants.

Many larvae may be destroyed by the digestive juicebut many others survive to cause intestinaldestruction.

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2- Urinary myasis

The larvae of some 36 species of fly have beenfound in the urine; urethral infections are probablydue to the invasion from the genitalia.

3- Cutaneous myasis

The larvae of some 36 species of fly have beenassociated with cutaneous myasis. These larvaeare able to burrow through necrotic or healthy

tissues. Their progressive is facilitated by a secondary

bacterial infection and possibly by their proteolyticsecretions.

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Diagnosis of Myasis

The identity of the parasite causing a particular

myasis may be determined by rearing the adultfly from the larvae, except in case of obligationparasites that cannot be separated from thehost.

Their identity can also be determined from themorphology of the larvae itself, particularly the

morphology of the posterior spiracles. The part containing the spiracle should be

removed from the larva, treated overnight withsodium or potassium hydrate, washed andfinally mounted for microcopic examination.

Prof HL Kamga 131

Field improvised debridement

During the First World War, it was notedthat maggots infected wound healed morerapidly than other, probably because themaggots eat up the death tissuestherefore reducing secondary bacterialinfections.

Maggots were used in deep tissues ofsoldier, and after war, they were used forsimilar purposes on civilians. Eventuallyflies were reared under sterile conditionsand used in treatment of chronicosteromyelitis.

Prof HL Kamga 132

Maggot therapy used in a small wound

In controlled and sterile settings, maggottherapy (also known as MaggotDebridement Therapy (MDT), larvaltherapy, larva therapy, or larvae therapy)introduction of live, disinfected maggots orfly larvae into non-healing skin or softtissue wounds of a human or other animal.

This practice was widely used before thediscovery of antibiotics, as it serves toclean the dead tissue within a wound inorder to promote healing.


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Forensic

Some types of maggots found on corpsescan be of great use to forensic scientists.By their stage of development, thesemaggots can be used to give an indicationof the time elapsed since death, as well asthe place the organism died. The size ofthe house fly maggot is 9.5-19.1 mm (3/8to 3/4 inch). At the height of the summerseason, a generation of flies (egg to adult)may be produced in 12-14 days.

Prof HL Kamga 134

Maggots are classified using "instar"stages. An instar Iis about 2-5 mm long;instar II6-14 mm; instar III15-20 mm.

These correspond to an age of 2-3 days,3-4 days, and 4-6 days (for average houseflies or bottle flies) since the eggs werelaid.

Some forensic scientists use this data todetermine the approximate time of deathof a human body.

Prof HL Kamga 135

Control of myasis

Sreaming of susceptible young domesticanimal, treatment of wounds.

Persons with catarrh or superlativelesions should not sleep in open air

The eggs or larvae deposited on hair orskins may be destroyed by Kerosene.

In cuteneous myasis, the larva

paralyzed with chloroform or cocainemay be extracted by manual pression.

Antihelmenthic drugs may be used forintestinal forms

Prof HL Kamga 136

Chapter 7: CLASS CRUSTACEA

A/ Cyclops

Cyclops is a water flea measuring about0.5mm long. The cephalothorax is ovoid bearingup to 5 segments, a pair of antennae and adouble tail. Cyclops are free living aquaticarthropods seen more abundantly during dryseasons in shallow ponds, step wells and openwells.

Illustration of a Cyclops

Prof HL Kamga 137

Cyclops and Diseases

Cyclops has been shown to be the developmental host ofDracunculus medinensis. Dracunculus medinensis, the guineas worn is a

common parasite endemic in the tropics. Although a tissuesparasite resembling the filaria, it does not have a truemicrofilarial stage.

The small male worms are rarely several monthsdevelopment in the internal connective tissues, appear inthe subcutaneous tissues.

The skin of the ulcerates at the anterior end of the wormand larvae escape, usually when the leg is submerged inwater.

These larvae developed in the Cyclops. If humans drinkwater containing practices cyclops, infection occurs. Thechitenous membrane of the Cyclops will help overcome theacidity of the stomach.

Prof HL Kamga 138

The released larvae penetrate the duodenal

mucosa and develop in the loose connectivetissue. The worms are very long with the females

measuring up to 2mm width. The male is muchsmaller and inconspicuous (2cm).

The human infection, possibly the fiery serpentof the Bible is associated few symptoms whichusually subside when the lesion erupts on theleg or the arm and the female worm emmerges.

If the worm is removed, healing usually occurswithout any problems.

If the worm is damaged or broken duringremoval, there may be intense inflammatoryreaction with possible cellulitis along the wormsmigratory tract. This can result in arthritis andsynovitis.


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In some region of the female worm is gradually removed from

the tissues by rolling it up on the stick

Prof HL Kamga 140

Prawn (craw-fish) This is crustacean bearing a long narrow curved

segmented body. The head bears two pairs ofantennal and a pair of stalked eyes.

Thoracic segments bear eight pairs appendagesthe first 3 bearing maxillipeds for feeding, whilethe remaining five act as walking legs (chela).The abdomen bears five pairs of paddle-likestructure (swimmerets) while the last segmentbears a fan shaped tail(telson) for swimming.

The prawn is a familiar aquatic arthropod livingin rivers and streams, feeding on dead, organicmatters. The common genera Palaemonhasbeen shown to serve as larval developmentalhost for the lung fluke, Paragonimus species.

Prof HL Kamga 141

Illustration of a prawn

Prof HL Kamga 142

THE END.

Thank you for your attention

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