The below mentioned article provides a short note on Genus Schistosoma (Blood Fluke).
Morphology of Genus Schistosoma (Blood Fluke):
It comprises:
1. Schistosoma haematobium — causing schistosomal haematuria.
2. S. mansoni, and 3. S. japonicum (intestinal schistosomiasis).
S. haematobium is in the vesical venous plexus. The male adult is shorter (10-15 mm x 0.8-1 mm) and stouter, is covered with minute integumentary tuberculation’s, and has two suckers (Oral sucker Fig. 108.20; ventral sucker is larger, Fig. 108.20a), a gynaecophoric canal in which the female is held during copulation (Fig. 108.20b).
The female is long (20 x 0.15 mm) and slender (Fig. 108.20c). Egg (size 112-170 µ x 40-70 µ) has a distinct terminal spine (Fig. 108.21).
Life cycle requires 2 hosts:
1. Man (definite host);
2. Fresh water snail (intermediate host). When eggs are discharged in the water during micturition by the infected person; the ciliated larva (miracidium first stage larva Fig. 108.27) is hatched out and infects the snail on contact, reaches the liver, develops into sporocyst (second stage larva) and finally into bifid tailed cercaria (Fig. 108.26) which breaks out of the snail.
It comes in contact with the human skin, while the man wodes the cercaria infested water, enters the skin, transforms into tailless cercaria (Schistosomule infective form to man) and enters into the circulation in the intrahepatic portal vessel, there it becomes sexually mature, reenters the blood stream and settles in the vesical venous plexus.
The male holds the female within the gynaecophoric canal for mating and the fertilised female lays eggs which work their way through the vessels and mucosa of the urinary bladder and are excreted through urine.
Clinical features:
The incubation period is 10-12 weeks. Irritation, minute haemorrhages at the site of entry on the skin followed by anorexia, headache, malaise, pain in the back and limbs, fever, night sweating.
Laboratory diagnosis:
(1) Microscopic demonstration of terminal spined eggs in the urine deposit and in biopsied vesical mucosa. Ultrasonography can also be done.
Serological Tests:
Besides, CFT, intradermal, precipitin, HA, bentonite or flocculation tests, recent ELISA, CIEP tests can also be used for diagnosis of schistosomiasis.
Treatment:
Praziquantel is recently used anthelminthic agent. S. mansoni, Fig. 108.22, (Manson blood fluke in vein of sigmoid rectal area) and S. japonicum, Fig. 108.24, (oriental blood fluke in superior mesenteric vein) resemble S. haematobium.
Egg is characterised by lateral spine (S. mansoni Fig. 108.23) by abbreviated spine on the upper right border of the shell. (S. japonicum, Fig. 108.25). Life cycle of S. mansoni and S. japonicum parallels that of S. haematobium, but their eggs are passed in the faeces.
Clinical features:
Clinically both these flukes cause dysentery, no haematuria.
Laboratory diagnosis and treatment are similar to those of S. haematobium.
Other Trematodes, Heterophyes Heterophyes (Fig. 108.28) and its egg (Fig. 108.30); Metagonimus yokogawai (108.29) and its egg (108.31). 