Parasitology Exam2 Lecture4 T. Yoshino SCHISTOSOMIASIS (= Bilharziasis) Phylum= Platyhelminthes (parasitic flatworms) Class= Digenea (digenetic trematodes or ?flukes?) Genus= Schistosoma spp. (blood flukes) Schistosoma additional General Info Separate sex ?schistosoma? literally means ?split body? part of the ?neglected tropical diseases? 200 million infected worldwide 770 million at risk to infection S. mansoni studied most at UW Obligate parasites, amplifies transmission No metacercariae, nor any stage that needs to be eaten In Wisconsin, we have Schistosomal dermatitis (Swimmer?s itch), but we are not the DH Geographic distribution *Schistosoma haematobium ? Africa, Middle East (scattered) *S. mansoni ? Africa, Middle East, South America (Venezuela, Brazil), Caribbean *S. japonicum ? China, Philippines, Indonesia *S. mekongi ? SE Asia S. intercalatum ? Africa *causative agents of the vast majority of human infections worldwide Basic schistosome life cycle Egg (containing miracidium) -> hatches in freshwater -> miracidium (infective stage) -> directly infects snail intermediate host (asexual development; sporocysts, cercariae) -> cercariae (infective stage) released into water -> directly infects mammal (human) host (sexual development; adult worms) NOTE: Cercariae must find a host quickly as they cannot live that long in the water. How do they accomplish this? Adaptations: swim on the surface, are able to sense any disturbance in the water Why is the Egg Stage Important? Thin shelled with spines on them. They allow parasite to get from the blood circulatory system to other parts of the body Eggs stages flow into the intestine and the liver as well Results in major pathology Egg antigens attract immune cells, which cause a severe inflammatory response Leads to spotted very large liver Same thing can happen to spleen (can double, triple in size) Because of immune stimulation ?Unique? features of schistosome Lives in the blood vascular system Adult worms are dioecious (separately sexed) Cercariae directly infect the definitive host (lacks metacercarial stage) INTESTINAL SCHISTOSOMIASIS - Pathology Fibrosisimpaired circulation, hypertension Ascites Liver dysfunction Hemorrhage In Children Delayed growth Delayed mental development Long term infection Adult worms can live up to 40 years in human Primary stategy for control: mass drug treatment (MDT) Drugs available ? very effective > praziquantel (Drug-of-choice) > oxamniquine (alternative) > artemisinins (anti-malarials; in trials) Additional Control Strategy Info Control Strategies Vaccines-little progress Chemotherapeuticstreatment control Sanitationprevention control Snail controlprevention control Parasite hard to control due to its complicated metabolic processes Over time they start to resist even the best drugs Epidemiology Young people important to epidemiology Hard to keep kids away from infected waters Young immune system, they pass more eggs in feces More susceptible to parasite Species Location Disease Snail Host S. haematobium pelvic veins urinary schistosomiasis Bulinus S. mansoni mesenteric veins intestinal schistosomiasis Biomphalaria S. japonicum Similar to S. mansoni Oncomelania S. mekongi ? ? ? ? S. intercalatum ? ? ? ?
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