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Introduction to Parasitology
By Sh. Ghaffari
September 2012
Parasitology: definition Parasitology: study of parasites Animals:
Free-living Symbiotic
Symbiosis
Phoresis(to carry)
Commensalism(eating at the same table)
Mutualismpositive reciprocal relationship
ParasitismMetabolic
dependence
Parasitism
Parasite (parasitos “para: beside; sitos: grain or food”)
Host
Parasitism: a form of symbiosis in which one organism (parasite) benefits at the
expense of another organism of different species (host).
Must be:1. Animals2. Different species
Medical Parasitology
Life cycle1.Direct life cycle2.Indirect life cycle Parasite
Adult form/ Sexual reproduction
Larva/ Asexual reproduction
Larva
Adult
Egg
Transfer or paratenic
host
Medical Parasitology Host specificity
Host:1. Reservoir host 2. Incidental host
Zoonosis
Transmission : Direct contact Indirect contact Vector (carrier): often an arthropod,
1. Biological V.2. Mechanical V.
Medical ParasitologyMedical Parasites:1. Protozoa
2. Helminthes:1. Nematodes(Roundworms)2. Trematodes(flukes)3. Cestodes(tapeworms)
3. ArthropodaEctoparasitesEndoparasites
Platyhelminthes
Classification
Kingdom (Animal)
Phylum (Platyhelminthes)
Class (Trematoda)
Order (Digenea)
Family (Schistosomidae)
Genus (Schistosoma)
Species (heamatobium)
Binomial nomenclature
The scientific naming of species whereby each species receives a Latin or Latinized name of two parts, the first indicating the genus and the second being the species. the genus (capitalized) and species (lowercase) names, both written in italics.For example: Sarcocyctis bovis, Leishmania donovani,
Nematodes
Parasitic nematodes
Life cycle:
Cylindrical, Complete
digestive system,
Male < Female Large (parsites) Long life
L3
L4
Adultsegg
L1
L2
molting
molting
molting
Ascaris lumbricoides
Ascariasis
Ascaris lumbricoides: like Lumbricus Female: 20-35cm, Male: 10-20
Anterior end of Ascaris lumbricoides showing mouth, esophagus, and intestine.
Importance
Worldwide Very common parasitic worm in human: 1/6 of
world population Tropical and subtropical, poverty
worms
Need wet warm soil Resistant to cold weather Resistant to acids and alkalis
as well as other chemicals
Fertilized eggs oval to round , albumin thick outer shell
Unfertilized eggs
Small intestine: Ascaris larva emerging from egg
Ascariasis
Infection or disease?
Number of worms
Ascariasis: Symptoms and signs 1- Migrating larvae: allergic and respiratory
symptoms (Loffler syndrome):
Cough Sever hemorrhagic pneumonia allergic hypersensitivity reactions(parasite
proteins are allergenic): Asthmatic attacks. Pulmonary infiltration. Urticaria . Edema of the lips. Eosinophilia
Ascariasis: Symptoms and signs
2- Adult parasites in the intestine: A vague abdominal discomfort. Nausea. Colic Lactose Malnutrition Intestinal obstraction
Ascariasis: Symptoms and signs
Adult worms outside of the intestine (wandering worms: High infection, Only male / Fever, Drugs) :
carry intestinal bacteria to these sites Bile duct: jaundice, hepatitis Appendix and peritonea: appendicitis,
peritonitis Migrate forward through the intestinal
tract: vomited up or emerging through the nose.
Diagnosis Stool Examination: appearance of the eggs in
feces
Treatment Albendazole : single dose 400 mg/ 200 mg under 2
years Mebendazole: 100mg Bid x3 days Ivermectin pyrantel pamoate: single dose
Biliary ascariasis
Transmission
Children 5-9 years old poor sanitation (sewage disposal) places where human feces are used as
fertilizer poor personal hygiene consuming contaminated vegetables or fruits
Control
Effective sewage disposal systems. Wash, peel, or cook all raw vegetables and
fruits grown in soil Periodic treatment
Enterobius vermicularis Pinworm, Oxyur
Enterobiasis
Enterobius vermicularis
World wide distribution The most prevalent worm in USA and Western
Europe Incidense: 11.4% among people of all ages in
USA Most in School-age children (30-60%) Not associated with social class, or culture
Enterobius vermicularis Female:
about 1 cm sharply pointed tail
Male: About 0.5 cm curved tail
Contains developing embryo or a larva Colorless Adheres to environmental objects
Enterobius eggs
Infective in 4-6 h remain active up to three weeks
11
Clinical manifestations
No symptoms in most people Anal itching in children Restless sleep Itching and vaginal discharge
in girls Irritated or infected skin
around the anus
Diagnosis Treatment
Tape test (Scotch ) transparent adhesive
tape Done in the morning,
before defecation and washing
Adult worms in perianal skin
Mebendazole Albendazole pyrantel pamoate
single dose entire household be
treated repeated after 2 weeks
Control Eggs can be transferred from
fingers to clothing, bedding, towels, toilets, and other objects in the environment.
Spread by children to schoolmates or family members.
Dust containing eggs can become airborne
personal hygiene. laundering of bedding
close contact Finger sucking and nail biting Autoinfection(infection from the original host to
itself): anus-to-mouth rout retroinfection,(larvae may hatch on the anal mucosa,
and migrate up the bowel)
THE END
