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PARASITOLOGY LECTURE 9 – Cestode InfectionsNotes from W.U. DeLeon, J.A. SolonUSTMED ’07 Sec C – AsM
HYMENOLEPIS NANA (dwarf tapeworm)
smallest tapeworm infecting man only human tapeworm which can complete its
entire life cycle in a single host does not require an obligatory intermediate host man can harbor both adult and larval stages of
parasite
DISTRIBUTION
worldwide among children
DISEASES
hymenolepiasis
MORPHOLOGY
1. Adult Worm- found in the ileum- delicate strobila that measures 25 to 45 mm x 1
mm (lw)- Scolex
o Subglobularo 4 cup-shaped
suckerso retractable
rostellum with a single row of 20 to 30 y-shaped hooklets
- Necko long and slender
- Proglottidso Anterior = shorto Posterior = broadero Measures 0.15 to 0.3
mm x 0.8 to 1.0 mm (lw)
o Mature proglottids : contain 3 ovoid testes and one ovary
o Gravid proglottids : testes and ovary disappear uterus hollows out and becomes
filled with eggs segments are separated from
the strobila and disintegrate as they pass out of the intestines, releasing eggs in stool
- Segments o 175 to 220 segmentso genital pores found along the side of
segments
2. Eggs
- Shape : spherical or subspherical- Measures 30 to 47 um in diameter- Oncosphere
o thin outer membraneo thick inner membrane with conspicuous
bipolar thickenings 4 to 8 hair-like polar filaments
arise filaments are embedded in the
inner membrane
H. nana cysticercoid
LIFE CYCLE
- Dual pathway
1. Direct host ingests eggs which hatch in the duodenum
liberated embryos penetrate mucosal villi develop into infective cysticercoid larvae larvae break out of villi and attaches to intestinal
mucosa 4 to 5 days later develop into adults
2. Indirect infection is usually via accidental ingestion of
infected arthropod intermediate hosts like rice and flour beetles (Tenebrio sp.)
cysticercoid larvae are released and will eventually develop into adult tapeworms in the intestines of the host
- takes 20 to 30 days from time of ingestion for eggs to appear in the feces
- eggs are viable immediately after discharge from bowel
- autoinfection can occur through the fecal-oral route or w/in the small bowel
- oncospheres from eggs are released and they invade the host villi to start new generation
PATHOGENESIS AND CLINICAL MANIFESTATION
symptoms are produced because of patient’s immunological response to the presence of the parasite
asymptomatic – light worm burden clinical manifestations:
o headacheo dizzinesso anorexiao pruritus of nose and anuso diarrheao abdominal paino pallor
infected childreno restlesso irritableo exhibit sleep disturbanceso convulsions (rare)
Heavy infectionso Enteritis due to necrosis and
desquamation of the intestinal epithelial cells
Regulatory immunityo (time) clears H. nana spontaneously.
DIAGNOSIS
specific diagnosis = demonstration of characteristic eggs in stool
light infections = need to concentrate stool specimens
proglottids are not recovered because they undergo degeneration prior to passage with stools
TREATMENT
*Praziquantel = 25mg/kg single doseo causes vacuolization and disruption of
tegument in the neck regiono dosage for hymenolepiasis is higher than
for taeniasis because of relative resistant cysticercoids in the intestinal tissue
examine stool after 2 weekso repeat treatment to cover for the worms
emerging from remaining viable cysticercoids
EPIDEMIOLOGY
found in warm countries o Southern USAo Latin Americao Mediterraneano East Asiao Philippines
Transmission : poor sanitation, overcrowding, poor personal hygiene
Direct contact plays an important role because eggs cannot survive long outside host
Familial and institutional infection Found in mice and rats
PREVENTION AND CONTROL
involves a single host and transmission is direct personal hygiene and environmental sanitation rodent control prevent food from infections by grain beetles
HYMENOLEPIS DIMINUTA (rat tapeworm)
cosmopolitan parasite primarily of rats differs from H. nana in that it requires an
intermediate host
DISEASE
Hymenolepiasis – due to accidental human infections
MORPHOLOGY
1. Adult - larger than H. nana- Measures : 60 cm in length- Scolex :
o Has a rudimentary unarmed rostellum
- Proglottids :o Broader than longo Arrangement of sexual organs is similar
to H.nanao Larger than H. nana may reach 7.5mm x
3.5 mm (lw)o Unilateral genital poreso Gravid proglottids:
@ contains a sac-like uterus filled with eggs.
2. Eggs- Shape : circular- Measures 60 to 80 um- Bile-stained- Oncosphere
o Enclosed in an inner membrane
o Has bipolar thickenings
o Lacks bipolar filaments- Hooklets have a fan-like arrangements
LIFE CYCLE
Gravid proglottids separate from the main body of worm disintegrates release eggs in feces
Eggs are ingested by a wide range of adult and larval insects
o Fleas, beetles, cockroaches, mealworms and earwigs
Once ingested, they develop into cysticercoid larvae
When infected insects are ingested by rats or man, larva is released
Develops into adult worm in ~ 3 weeks
PATHOGENESIS AND CLINICAL MANIFESTATIONS
worm burden in rodents is relatively low in man, the highest number recorded is 19 worms manifestations are minimal and non-specific
DIAGNOSIS
based on identification of eggs from stool H. diminuta eggs are more circular, larger and lack
bipolar filaments At times the whole worm is expelled and the
scolex may be used in diagnosis
TREATMENT
similar to H. nana = Praziquantel 25mg/kg single dose
EPIDEMIOLOGY
human infections occur worldwide but more common among children
in poor countries with rat infestations occurs by accidental ingestion of grain beetles
infesting dried grains, dried fruits, flour and cereals
prevalence in Phil in rats is 8%
PREVENTION AND CONTROL
rodent control elimination of insect intermediate hosts protection of food sanitary disposal of waste
DIPYLIDIUM CANINUM (double pored tapeworm)
very common intestinal parasite of dogs and cats
DISEASE
Dipylidiasis in humans is accidental
MORPHOLOGY
1. Adult worm- Color : pale reddish- Measures 10 to 70 cm
in length
- Scolex : o Smallo Globularo 4 deeply cupped
suckerso protrusible
rostellumo 1-7 rows of
rosethorn-shaped hooklets
- Proglottids:o Narrowo 2 sets of male and
female reproductive organs
o bilateral genital pores (hence double pored tapeworm)
o Gravid proglottids Shape :
pumpkin seed Filled with
capsules or packets of 8 to 15 eggs enclosed in an embryonic membrane
2. Eggs- Shape : spherical- Thin-shelled- Hexacanth embryo
LIFE CYCLE
when gravid segments are detached, they either:o migrate out of the anuso passed out with feces
ova are released by:o contraction of the proglottid oro disintegration outside the host
egg capsules may remain in the fur of the host o larval fleas feed on epidermal debris
Intermediate hostso Ctenocephalides canis (dog flea)o Ctenocephalides felis (cat flea)o Pulex irritans (human flea)o Trichodectes canis (dog louse)
In the arthropod host, the hexacanth embryo develops into cysticercoid larvae
o Able to survive flea’s developmento When ingested, the cysticercoid is
liberated and becomes an adult in 3 to 4 weeks
PATHOGENESIS AND CLINICAL MANIFESTATIONS
infection rarely multiple symptoms are minimal
o slight intestinal discomforto epigastric paino diarrheao anal prurituso allergic reactions
some are asymptomatic
DIAGNOSIS
recovery of gravid proglottids passed out single or in chains
proglottids may crawl out of anus or passed out involuntarily
proglottids should be pressed or flatted between 2 glass slides for examination
Stool examination is not recommended since gravid proglottids do not disintegrate in intestines but in the environment
Egg capsules are rarely recovered
TREATMENT
Praziquantel = 5 to 10 mg/kg single dose
EPIDEMIOLOGY
human infections rare but reported in:o Europeo USAo Argentinao Rhodesiao China o Philippines
Infants and young children usually infected Observe actively motile proglottids in feces or
underwear Adults are not commonly infected because of age
tolerance against the parasite
PREVENTION AND CONTROL
periodic deworming of pet cats and dogs insecticide dusting of dogs and cats against fleas
DIPHYLLOBOTHRIUM LATUM (fish tapeworm or broad tapeworm)
belongs to order Pseudophyllidea one of 13 species that infects humans
DISEASE
Diphyllobothriasis – intestinal infection with the adult worm
MORPHOLOGY
1. Adult- Measures 3 to 10 m length- Up to 4000 proglottids
- Scolex : o Shape: spatulateo Measures 2 to 3 mm x 1 mm (ld)o Has 2 bothria or sucking grooves located
dorsally and ventrally
- Neck :o Long and attenuated
- Proglottids:o Immatureo Mature
Longer width than length Measures 2 to 4 mm x 10 to 12
mm (lw) Contains one set of reproductive
organs Testes
Located at dorsolateral part of proglottid
Vas efferens converge to form a vas deferens enlarge into seminal vesicle terminates in muscular cirrus (at midventral genital pore)
Ovary Symmetrical Bilobed Present at posterior
third immediately above Mehlis’ gland
o Gravid Uterus
Dark Rosette-like Coiled Located at middle Extends from ootyle
and opens through uterine pore behind common genital pore
Proglottids disintegrate only when the segment has completed its reproductive function
2. Eggs- Color: yellowish brown- Moderately thick shell- Inconspicuous operculum- Opposite operculum is a knob-like thickening- Measures 66 x 44 um
LIFE CYCLE
with disintegration of uterus, the uterine pore is relaxed and unembryonated ova are discharged
approx. 1,000,000 may be released daily ova complete development in water release free-swimming coracidium (a ciliated
embryo) ingested by copepods of genera Cyclops and
Diaptomus a procercoid larva develops in copepods
o still retains 3 hooklets in the cercomer (a caudal attachment organ)
copepod ingested by fish procercoid larva migrates to tissues
and develops into plerocercoid larva in muscles and viscera
plerocercoid larva appears glistening, opaque, white and unsegmented
fish is ingested raw by definitive host :man, dog, cat, other mammals
Paratenic hosts : carnivorous fish 2nd Intermediate hosts (fish)=perch, trout, salmon
& pike The plerocercoid attaches to the intestinal wall
and reaches maturity in 3 weeks within the definitive host
PATHOGENESIS AND CLINICAL MANIFESTATIONS
usually limited to one worm
infected individuals may be asymptomatic
symptomso nervous
disturbanceso digestive
disorderso abdominal
discomforto weight losso weaknesso anemia
symptoms may be due to absorbed toxins or byproducts of degenerating proglottids or due to mucosal irritation
infection results ino hyperchromic,
megaloblastic anemia with thrombocytopenia and leucopenia
o anemia seen is typically similar to that seen in Vit B12
deficiency
worms in jejunum compete effectively with the host for Vit B12
if worms are pushed down the intestines with treatment, anemia is relieved
Vit B12 content of D. latum is 50 x of T. saginata
DIAGNOSIS
- suggestive: residence or travel to endemic area raw fish diet
pernicious type of anemia
- definite diagnosis:o finding characteristic operculated eggs o or proglottids in stoolso sometimes proglottids may be vomitedo direct fecal smearo Kato technique to demonstrate eggs
- differential diagnosis (anemia due to diphyllobothriasis from pernicious anemia)
o examination of gastric juice for presence of free hydrocholoric acid
o pernicious anemia is associated with achlorhydria
TREATMENT
Praziquantel – 5 to 10 mg/kg single dose
Criterior : recovery of scolex in feces after treatment
If scolex is not recovered, repeat stool examination after 3 months to be certain that patient is no longer infected
EPIDEMIOLOGY
human infection is dependent on:1. presence of human or animal definitive hosts2. presence of suitable intermediate hosts3. dietary habits4. amount of pollution of fresh waters5. preference for eating raw fish 6. lack of sanitary toilet facilities
Reservoir hostso Dogso Catso Bears
prevalent in temperate zones Baltic countries: Switzerland, Romania, Danube
basin Asia : Russia, Turkistan, Israel, Manchuria, Japan Americas: Chile, Argentina, N. American states,
Canada Philippines – 7 cases
SPARGANOSIS
larval infection with plerocercoid larvae (aka spargana of pseudophyllidean tapeworms under Genus Spirometra)
involved in human sparganosis
o Spirometra mansonio Spirometra erinaceio Spirometra ranarum
MORHOPHOLOGY
Adults are intestinal parasites of cats, dogs, and other carnivores
Adults are usually mistaken for D. latum
Spargana showed typical solid body with worm-like appearance
Pseudosegmentation with a slit-like invagination at the head end
Larvaeo Opaque, glistening, whiteo Found in any part of the bodyo Most commonly found in the eye,
subcutaneous tissue, muscular tissues of thorax, abdomen, thighs, inguinal region and in viscera
proglottid scolex
S. mansoni eggs
LIFE CYCLE
Human infected through1. drinking water containing Cyclops or
copepods infected with procercoid larvae2. eating infected 2nd intermediate hosts like
frogs, toads or snakes containing plerocercoird larvae
3. applying plerocercoid infected flesh of frogs and snakes as poultices in sores in the eye, vagina, and skin penetration into cutaneous tissues
4. consumption of infected flesh of pratenic hosts (wild pigs)
PATHOGENESIS AND CLINICAL MANIFESTATION
- Symptomso Complain of painful edema due to
migrating larvaeo Local indurationso Periodic giant urticariao Edemao Erythema with chills, fevero High eosinophilia
DIAGNOSIS
Finding white larvae in the lesion Species identification done by experimental
infection of animals
TREATMENT
- Surgical removal of plerocercoid- In cases reported, spargana were motile upon
excision of the mass
PREVENTION AND CONTROL
- Drinking boiled or filtered water- Proper cooking
