Fig. 107.—Ovum of Schistosoma japonicum. By J. A. Thomson. (Jefferys and Maxwell.)
Recently Leiper has found cercariae showing the absence of a pharynx (characteristic of the genus) in a Japanese mollusc. Such molluscs were teased out in water and laboratory bred mice immersed therein. One of these mice was killed a month later and adult schistosomes were found in the portal vessels. Leiper has also found cercariae showing absence of pharynx in four different species of molluscs in Egypt. With such molluscs he was able to infect white rats and other animals. He states that infection with these cercariae from the mollusc host can bring about infection either by way of the mouth or through the skin. Sodium bisulphate in a strength of 1 to 1000 killed these cercariae almost immediately.
It would therefore seem proven that all human schistosome infections take place following cercarial and not miracidial development. As proof that S. haematobium and S. mansoni are different species, Leiper notes that mice infected by molluscs of the genus Bullinus showed schistosomes with terminal spined eggs, the ovary lying in the lower half of the female. The male had four or five large testes. In mice infected by molluscs of the genus Planorbis, the eggs were lateral spined, the ovary was in the anterior half of the body and the male had eight small testicles.
The mollusc host of S. japonicum is Blanfordia nosophora. The shell of this snail is of cornucopia shape.
As these flukes are found in the blood vessels they are often referred to as the blood flukes.
History
Vesical schistosomiasis has undoubtedly existed in Egypt since ancient periods as vesical calculi are frequent in the mummies of various dynasties. Ruffer has found calcified schistosome ova in the kidney of a mummy.
The French troops suffered greatly from the disease in 1800. It was Bilharz in Cairo, in 1851, who first associated the haematuria with the presence of the parasite and it is from his name that we get the designation bilharziasis or bilharziosis for the disease.
In 1903, Manson found lateral spined eggs in a patient from the West Indies who was suffering from rectal rather than bladder symptoms. In 1907 Sambon, considering the points of difference between the eggs and the involvement of rectum rather than bladder, established a new species, S. mansoni.
In the West Indies, as shown by the reports of Surgeon Holcomb from Porto Rico, rectal bilharziasis is rather common.