Lecture 9: Schistosomiasis PDF

9th LECTURE Schistosomiasis  Causal Agents Schistosomiasis is caused by digenetic blood trematodes : Schistosoma Spp.  Systematic position Phylum: Platyhelminthes Class: Trematoda Genus: Schistosoma (S.) 5 species can infect human: – S. haematobium – S. mansoni – S...

9th LECTURE Schistosomiasis  Causal Agents Schistosomiasis is caused by digenetic blood trematodes : Schistosoma Spp.  Systematic position Phylum: Platyhelminthes Class: Trematoda Genus: Schistosoma (S.) 5 species can infect human: – S. haematobium – S. mansoni – S. japonicum – S. mekongi – S. intercalatum  Geographic Distribution Schistosoma mansoni : is found in parts of South America and the Caribbean, Africa, and the Middle East. Schistosoma haematobium : in Africa and the Middle East. Schistosoma japonicum : in the Far East. Geographic Distribution…… cont.  Morphology of Schistosoma Adult Worm Separate sex (male and female worms) The male has a gynecophoric canal in which it carries the female during the life cycle. 10-20 mm long. Male & Female together 8 Comparisons among Schistosoma Females 9  Comparisons among Schistosoma males S. haematobium S. mansoni S. japonicum 10  The Egg Oval (S. haematobium & S. mansoni) or Round (S. japonicum) Translucent Contains mature miracidium With terminal spine (S. haematobium), lateral spine (S. mansoni), or rudimentary lateral spine (S. japonicum)  Miracidium Pyriform Ciliated ~200µm long  Intermediate hosts of Schistosomes S. Mansoni S. Haematobium S. Japonicum Biomphalaria sp. Bulinus sp. Oncomelania sp. 13 Intermediate and Reservoir hosts  Sporocyst Sac- like Contain germinal cells masses  Cercaria Has a body (head) and tail Has furcocercous ( forked) tail. 400-600µm long.  Life cycle In human (Definitive host), cercariae migrate through circulatory system and finally male & female mature and pair up in the blood capillaries of liver. The couple migrate against the blood stream direction to favored site where female deposit eggs mainly in: - mesenteric venules of large bowel & rectum (S. mansoni). - mesenteric venules of small intestine (S. japonicum), or - pelvic and vesical venous plexus (S. haematobium). About 50% of deposited eggs passed out of body and 50% trapped in tissues. Eggs are released with faeces (S. mansoni & S. japonicum) or urine (S. haematobium).  In fresh water and under optimal conditions the eggs hatch and release miracidia, which swim and penetrate specific snail intermediate hosts: Biomphalaria sp. (S. mansoni), Bulinus sp. (S. haematobium), or Oncomelania sp. (S. japonicum). In the snail (intermediate host) asexual replication occur including 2 generations of sporocysts (mother & daughter) and the production of cercariae. Upon release from the snail, cercariae (the infective stage) swim, penetrate the skin of the human host , and shed their forked tail, becoming schistosomulae (Skin schistosomulae).  The schistosomulae migrate through blood vessel to the lungs (lung schistosomulae ) and then to the liver which mature to adult worm. Adult worms in humans reside in the blood venules in various locations, which at times seem to be specific for each species as mentioned previously. The females deposit eggs in the small venules of the portal and perivesical systems. The eggs are moved progressively toward the lumen of the intestine (S. mansoni and S. japonicum) and of the bladder and ureters (S. haematobium), and are eliminated with faeces or urine, respectively. Life cycle Life cycle Schistosoma spp. 21  Infective stage: Cercaria Infection route: Cutaneous Intermediate host(s): Snail Mode of Infection : Cercarial penetration of the skin. Infection site: Mesenteric venules of large bowel & rectum (S. mansoni) Mesenteric venules of small intestine (S. japonicum) Pelvic & vesical venous plexus (S. haematobium) 22  Clinical Features Acute schistosomiasis (Katayama's fever) occur weeks after the initial infection, especially by S. mansoni and S.japonicum. The acute reaction is due to the sudden release of large number of eggs. Manifestations include: – fever, –cough, –abdominal pain and diarrhea, –hepatosplenomegaly, –eosinophilia. Chronic infection Cause granulomatous reactions (trapping of eggs by a tissue) and fibrosis in the affected organs, which may result in manifestations that include: – colonic polyposis (small clumps of cells on the lining of colon)with bloody diarrhea (S. mansoni). – portal hypertension with hematemesis (vomiting of blood) and splenomegaly (S. mansoni, S. japonicum); – cystitis (inflammation of the bladder) and ureteritis with hematuria, which can progress to bladder cancer (S. haematobium). – pulmonary hypertension (S. mansoni, S. japonicum) – glomerulonephritis (inflammation of the kidney) (S. haematobium). – may central nervous system lesions. Hepatosplenomegaly  Laboratory Diagnosis Microscopic identification of eggs in stool (S. mansoni or S. japonicum) or urine (S. haematobium ) is the most practical method for diagnosis.  Prevention and Control Avoidance of wading (walking), bathing, swimming in or drinking polluted water. Wearing protective clothes (gloves, boots........). Quick and through drying of exposed skins. Avoiding defecation and micturition in water canals. Mass treatment of all infected cases. Control of Snail ( intermediate host) through: – Physical methods : changing the suitable environmental conditions like canal coverage – Biological methods :introduction of natural enemies as competitive snails or fish or crayfish – Chemical methods using molluscicides eg: copper sulphate  Learning outcomes By the end of the lecture, you should be able to: 1- Mention Causal Agent of schistosomiasis. 2- Mention systematic position of Schistosoma spp. 3- Mention geographic distribution of schistosomiasis. 4- Enumerate Intermediate, Definitive and Reservoir hosts of Schistosoma spp. 6- Explain life cycle of Schistosoma spp. 7- Mention habitat of Schistosoma spp. 8- Mention mode of infection by Schistosoma spp. 9- Mention pathology and clinical features of schistosomiasis. 10- Diagnose schistosomiasis. 11- Mention prevention and control means of schistosomiasis 32