Trematodes (flukes) Classifided into: 1-Blood flukes (Schistosomes) 2-Tissue flues

Blood flukes (Schistosomes) Species of schistosomes infect human 1- S. haematobium 2- S. mansoni 3- S. japonicum 4- S. intrcalatum 5- S. meckongi

General features of schistosomes 1-Adult worms are -elongated and resemble roundworms. -live in blood vascular system. -have separated sexes (diecious). -Posses an oral and ventral suckers. -body cavity is absent. -have highly developed and complex reproductive system. -have simple nervous and excretory systems. -Posses an incomplete alimentary canal; no anus.

2- The fundamental stages in life cycle are the egg, larva and the adult. -Egg is provided with spine but without operculum. -The larval stages are miracidium, mother and daughter soporocysts and cercaria (but no redia or metacercaria formation as in tissue flukes). 3- the forked tailed cercariae is the infective stage to man. 4-infect human by penetration of unbroken skin by cercariae.

Schistosomas in copula Morphology

Life cycle of Schistosoma Species

Pathogenesis and clinical features 1- egg deposition. 2-liberation of antigens of adult worms and eggs. -Retention of eggs in the blood vessels: 1-eggs wedged firmly into the small vessels. 2-Sharp spines. -Liberation of eggs from the tissues into the lumen of the intestine or bladder: 1- enzyme elaborated by the miracidium. 2- necrosis of the tissue caused by pressure. 3-the effect of the spine.

-Clinical manifestations of schistosomiasis 1-schistosome dermatitis 2-acute schistosomiasis 3-chronic schistosomiasis 1-schistosome dermatitis (swimmer’s itch) -cercariae of the blood flukes of aquatic birds 2-acute schistosomiasis ( Katayama fever) -Beginning of oviposition, usually 20 to 50 days after primary exposure. -flu like illness with fatigue, headache, arthralgia and night sweats, sometimes with hepatosplenomegaly, cough, dyspnea and chest pain.