BILHARZIASIS or SCHISTOSOMIASIS, a disease char acterized by hamaturia or by discharge of blood and mucus by the rectum caused by the fluke parasite schistosoma and endemic throughout Africa, South America and the West Indies, China, Japan, the Philippines, Formosa, Burma, India and Western Australia. One European country only, south Portugal, is known to be infected by schistosomiasis (1925).
Causation.—Schistosomiasis is caused by certain metazoal para sites of the family Schistosomidae Looss-1899 (type genus Schis tosoma Weinland 1858) belonging to the trematode class of the phylum Platy-helminthes. In the schistosomidae the sexes are separate, and the alimentary canal is united posteriorly into a single tube. In the known human species the egg is furnished with a characteristic spine (point) or knob. A ventral (gynaecological) canal for carrying the cylindrical female worm is formed by the infolding lateral margins of the leaf-shaped male.
There are three known human species ; Schist. haematobium, the chief African species infects principally the bladder; Schist. mansoni, also found in Africa, the only species infecting America, affects the large intestine; Schist. japonicurn, the Asiatic species, affects the large intestine and liver and spleen.
The adult worms inhabit the portal venous system, reach ma turity in the liver and pass in the portal tributaries to the pelvic veins in the bladder and large intestine to lay their eggs, which reach the exterior world in the urine and faeces. In fresh water under favourable conditions the ovum hatches the ciliated em bryo (miracidiurn) .
If during its short active life it approaches an appropriate water-snail, it penetrates and bores its way to the pancreatico hepatic gland and encysts. Bifid larvae (cercariae) develop within the daughter cysts and escape when the snail ruptures. The parasite again becomes free swimming. Cercariae survive not longer than 36 hours. They are attracted by and penetrate human skin and mucous membranes immersed in the water. They dis card the tail and are carried by the blood and lymph to the lungs and from thence to the liver where they mature. Definite symp toms of schistosomiasis may be expected two months or later from the time of contact with infected water.
Treatment.—In 1917 Christopherson in Khartum found that antimony tartrate administered intravenously was an infallible parasiticide for both species of Egyptian schistosomiasis, and worked out the method of treatment by antimony which has since been adopted. Later it was found that antimony tartrate was an equally trustworthy parasiticide for Asiatic schistosomiasis. Recovery is the rule provided reinfection is obviated. Death takes place from toxaemia due to a heavy infection, from inter current disease, from impairment of liver function, from compli cations caused by the damaged organs and secondarily from stone in the bladder or cancer.
Preventive Measures.—Theoretically schistosomiasis can be stamped out of a locality by (1) curing all the cases, (2) killing the intermediary hosts (water snails), (3) preventing the mollusc infecting man, and man the mollusc. This is effected by the in travenous injection of antimony tartrate (Pot. or Sod.) daily for five days, afterwards three times a week until the necessary total (adult) amount (25-30 grains) is reached. Antimony is contra indicated in cardiac and renal disease and when the liver is ex tensively disorganized. Emetin is given when antimony tartrate is not tolerated. Extermination of the snails is accomplished by chemicals which kill the mollusc but are beneficial to or do not interfere with the fertility of the soil, chiefly calcium and ammo nium compounds. In Egypt where irrigation is under government control, Leiper recommended the periodical drying up in rotation of irrigation canals for 5 days. The natural enemies of the snail (ducks) are to be encouraged. Water contaminated by bilharzia, if kept for two days, is innocuous f or domestic purposes.