Schistosoma
General: These trematodes have separate sexes (dioecious) and reside in the GI blood vessels of their definitive host; there is no secondary host, but there are snail carriers. Males and females both measure ~10mm in length, live in intraabdominal veins, and may live 20-30 years. One female may produce several hundred eggs per day; eggs extravasate into the GI tract or bladder (causing variable pain, inflammation, and hemorrhage, eventually fibrosis and organ failure) and are eliminated. Eggs which do not extravasate may be filtered by the liver, which develops reactive fibrous granulomas. They hatch in water and are taken up by snails; snails then eliminate the cercarial form which penetrates human skin and matures within intraabdominal vessels (about 6 weeks).
Clinical: Schistosomiasis is endemic across most of Africa, parts of SE Asia, NW South America, and the Caribbean.
- Normal:
- Abnormal:
Resistance:
Morphology: Eggs are very characteristic and confirm diagnosis. S. haematobium eggs in urine (55 to 65 by 110 to 170 micrometers) have an apical spine or knob. S. mansoni eggs in feces (45 to 70 by 115-175 micrometers) have a spine on the side. S. japonicum eggs (55 to 65 by 70 to 100 micrometers) are more round with a vague spine on the side.
Growth characteristics:
Common/important pathogens: