بسم الله الرحمن الرحيم

Schistosomaisis

Objectives Discuss the epidemiology and etiology of Schistosomiasis Describe transmission and life cycle of Schistosomiasis Discuss pathogenesis and brief clinical presentations of Schistosoma spp. Discuss the complications of Schistosoma spp. Explain lab diagnosis of Schistosomiasis

Classification of human parasites Human parasites divided into two groups – single celled protozoa – multicellular metazoa

Characteristic features of trematodes(flukes) Flat, leaf-like body that is not segmented Schistosomes are parasites that belong to this group

Trematodes classification Trematodes (flukes) Blood flukes (schistosomes) Hepatic flukes Intestinal flukes Lung flukes

Blood flukes (schistosoma) BloodFlukes Schistosoma haematobium Schistosoma mansoni Schistosoma japonicum A genus of trematodes, Schistosoma, commonly known as blood-flukes or bilharzia, includes number of species which are responsible for the disease schistosomiasis, and are considered by the World Health Organization as the second most important parasitic disease, next only to malaria, with hundreds of millions infected worldwide. schistosomiasis

Scistosoma anatomy Sexes are separate Female lies in a cavity in front of the male body known as gynacophoric canal

Schistosomes Also known as bilharzia Theodor Bilharz -( ) first described the parasites. Postal stamp released in Egypt, 1962 Issued on his 100th death anniversary

Geographic distribution  Schistosoma mansoni  Africa (52 countries), Middle east South America  Schistosoma japonicum  Far east  Schistosoma haematobium  Africa (54 countries),Middle east S. hematobium S. mansoni S. japonicum

Schistosomes are common in Africa and middle east esp. along the nile river

Transmission to humans Humans (acquire infection by swimming in water harboring the larval form called cercariae)

Definitive hosts Definitive host are ones in which the adult worm live and mate Adult worm lives in the blood stream(portal vein) of humans

Intermediate host Snails in water Intermediate hosts are one in which the larval forms develop

Schistosoma mansoni, S. japonicum, ……….Release eggs in intestinal tract and passed to the outside in the stool Schistosoma hematobium………… release eggs in urinary tract and thus passed to the outside through urine

Transmission  Presence of the snail host in water in which larval forms develop  One person Pollutes fresh water with excreta(urine or stool) containing Schistosome eggs  Other Human comes in contact with water infested with cercaria (which penetrates his skin)

Clinical features and pathogenesis Acute disease Chronic disease

Cercarial dermititis Skin penetration by cercariae dermatitis(swimmers itch)—within 24 hrs

Acute phase (Katayama disease) fever, chills, headache, anorexia, urticaria, and diffuse megaly, lymphadenopathy and diffuse vasculitis lesions 2-3 weeks after the infection and usually lasts 1-2 months (typhoid fever)

Dysentery in S mansoni and S japonicum infection bloody diarrhea---- Schistosoma mansoni, S. japonicum, ……….Release eggs in intestinal tract

Schistosoma hematobium Bloody urine----- hematuria In addition there is dysuria and frequency

Chronic disease-most important Hepatic dysfunction and portal hypertension from cirrhosis of the liver because of eggs in the liver

Pathogenesis of hepatosplenomegaly  Eggs that do not leave the body are swept to the pre-`sinusoidal capillaries of the liver and are trapped there  The immune system responds and walls off the eggs with a granuloma, the egg dies  Continuous stimulation of the immune system leads to fibrosis  Periportal fibrosis leads to portal hypertension  Portal hypertension leads to collateral circulation, eosophageal varices Granuloma in liver formed around a schistosome egg

Schistosome Pathology

Egyptian boy with hepatosplenomegaly, ascites fluid build-up and superficial collateral circulation ‘Intestinal’ asymptomatic schistosomiasis at the Egyptian village level The 2 faces of schistosomiasis

Schistosoma hematobium complications Granuloma formation and fibrosis at the lower end of the ureter obstructs urinary flow, with subsequent development of hydroureter and hydronephrosis High frequency of secondary bacterial infections of urinary tract.

Schistosoma hematobium is a known carcinogen Strong association with squamous cell carcinoma of bladder Chronic irritation leads to squamous metaplasia->dysplasia- >carcinoma

Lab Diagnosis Microscopic identification of eggs in stool or urine (S. hematobium) is the most practical method for diagnosis stoolurine

Schistosoma mansoni eggs These eggs have a characteristic prominent lateral spine near the posterior end. The anterior end is tapered and slightly curved. S. hematobium egg: In this species, the eggs are large and have a prominent terminal spine at the posterior end. S. japonicum egg the egg is typically oval and has a vestigial spine. Schistosoma japonicum eggs are smaller than those of the other species. Eggs

Lab Diagnosis( cond.) Serology for schistosomal antibodies. Two tests are available : the Falcon assay screening test/enzyme- linked immunosorbent assay (FAST-ELISA) and the confirmatory enzyme- linked immunoelectrotransfer blot (EITB). Esp for katayama fever

Treatment Praziquantel The dose is 20 mg/kg by mouth 2-3 doses in one day

Control measures/ Possible Points of Attack Sanitation, Water Supply & Community Health education; Hygiene Socioeconomic development ==> toilets & water systems Snail Control Molluscicides; Competitors/Predators; Habitat reduction/closed irrigation; Environmental modification