Trematodes (flukes)

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

Blood flukes (Schistosomes)

Species of schistosomes infect human1- S. haematobium2- S. mansoni3- S. japonicum4- S. intrcalatum5- 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.