TREMATODE – males & female versions exist (“Flukes”) INFECTIONS (Micro made easy pp 253)

In helminthic infections, the extent of clinical disease is directly proportional to the worm load, and the level of eosinophilia.

Think of Helminths as divided into two broad species: 1) Nematodes (round worms), 2) Platyhelminths (flat worms). Platyhelminths are further divided into: 1) Trematodes (flukes), 2) Cestodes (tapeworms).

Schistosoma (blood flukes): Causes schistosomasis. There are three species of this Helminth: 1) japonicum, 2) mansoni, 3) haematobium. This organism is found in freshwater. Eggs hatch here Q larvae settle in intermediate host (freshwater snail) Q larvae mature (called cercariae) and become infectious Q penetrate through exposed skin Q enter venous system Q portal system Qmature larvae mate here Q travel to veins around intestine and lay eggs here Qthese eggs enter lumen and are excreted via faeces Q life cycle continues. No immune system is mediated against mature larvae because they mimic host antigens on their surface.

Clinical features: Early: 1) swimmers itch (dermatitis), 2) Katayama fever, 3) Chronic fibrosis of organs + vessels where eggs are laid (intense immune response against eggs, granulomas formed, fibrosis occurs Q blocks portal system Q splenomegaly etc).

Diagnosis: 1) Send repeated stool samples to look for eggs, 2) Serology / high eosinophil count. Treatment: (Praise quantum physicists: ie: Praziquantel)

Category: Microbiology Notes