PRESIDENTIAL ADDRESS — SECTION D. 77 



SCHISTOSOMIASIS. 



Schistosomes have been known as parasites of man for many 

 _years, the earliest form to be recognised being Schistosoma hcema- 

 tohiwm, the casual agent of urinary bilharziasis. However, the first 

 life-history of a schistosome to be worked out was that of the 

 Asiatic schistosome, *S'. japonicutn. The adult worm was described 

 •by Katsurada in 1904. Its life-history was described by Miyairi 

 and Sudzuki in 1914. These workers found dark-shelled snails, 

 Blanfordia nosopJtora, containing cercariae. They obtained speci- 

 mens of the uninfected snails and exposed them to miracidia of 

 S. japomcuvi,, and traced the stages of their development into 

 cercariae like those found in nature in the snails. Mice were 

 immersed in the water in which the snails were kept, and adult 

 Schistosoma japonicum were found in them after a few weeks. 

 In 1914 Leiper confirined this work in Japan. In 1916 Narabayashi 

 showed that man, cattle, horses, pigs, goats and dogs could all 

 ;become infected naturally A\'ith S. japonicuni. 



The ova of S. japoyiicum are non-operculate, oval, with a very 

 small lateral spine or thickening that often is not noticed at all, 

 or may not be present, and a cap-like thickening at the opposite 

 ^nd. The miracidium hatches rapidly, swims in the water, and 

 further development takes place when it reaches the snail, 

 Blanfordia nosophora. Sporocysts are formed which produce cer- 

 ^^ariee. Each cercaria is an elongated oval body, with short lancet- 

 shaped bristles at the mouth. There is a small ventral sucker. 

 Three pairs of mucin glands are present, their ducts opening into 

 the mouth. The excretory system has been worked out chiefly 

 'by Faust, and is rather simpler than that of S. hcematohium. 



Narabayashi has shown that the cercariae penetrate the skin 

 of the vertebrate host and pass into the venous system. Thence 

 they reach the heart, pass through the lungs, and thence 

 -migrate through the diaphragm and liver into the portal system, 

 whence, after attaining sexual maturity, they migrate into the 

 .jnesenteric, vesical and other veins. 



The adult male, S. japonicum, is 8mm. to 19mm. long, and possesses 

 six to eight testes in the anterior of the bod jr. The cuticle of the male, 

 unlike that of S. hamatobiiim and S. mansoni, is relatively smooth, vvith 

 only a few spines and no marked bosses. The female is from 8 mm. to 

 '26 mm. long. The suckers possess fine spines. As in the male, the intes- 

 tine forks far back, and the single portion of the intestine is small. 



Schistosoma hcBmatobiiun is widely distributed in Africa and 

 also occurs in other parts of the world. For instance, it has 

 recently been imported into Australia by soldiers who contracted 

 the infection in Egypt, where the disease is extremely prevalent. 

 Cases also occur in South America, but are relatively few. In 

 Europe, through the .agency of returned soldiers, molluscan 

 infection has occiu-red, and new cases have arisen in Portugal. 



During the war, when there were many troops in the Eastern 

 -war zone, bilharziasis caused much trouble in Egypt. Leiper* 

 (1915) investigated the transmitters, and worked out that the 

 carrier of Schistosoma viansoni in Egypt, where there was bil- 



*Jovrnal Royal Army Medical Corps, xxv. 



