Studies on <i>Schistosomiasis japonica</i> and Saponins

Abstract

The molluscicidal activity of the bark of Entada phaseoloides and extracts from tubers of its related specie, Entada parvifolia against Oncomelania quadrasi, the snail intermediate host of Shistosoma japonicum in the Philippines were determined.

The commercial gogo bark applied to waters with O. quadrasi, in the proportion of 2 gms/liter will kill 100% of snails within 24 hours. At this concentration miracidia and cercariae of S. japonicum in the same waters will die within one hour, thus, making the water safe or noninfective for some time. At the dose 100 gms/sqm of water-covered terrestial snail habitats, provided previously cleared of vegetations, at least 90% of O. quadrasi will die within 24 hours. These measures can be practical on a self-help basis by inhabitants of schistosomiasis endemic areas where gogo plant grows or where its bark is marketed.

At dilution of 1:5,000 saponin extracted from tubers of E. parvifolia killed at least 90% of snails after 24 hours exposure while ethanol (crude saponin) and other extracts require at least 1:2,000 concentration to kill at least 90% of O. quadrasi. At these concentrations and the expenses and time involved in the preparation of these extracts, they are not economical or practical for large scale use of molluscicides.

It is suggested that methods of extraction and purification which require little time of preparation and a cheaper but of higher recovery rate of molluscicidal principles be developed.

Surveys of barrios in three towns of Leyte, endemic for Schistosomiasis japonica using the circum oval-precipitin test (COPT) and stool examination in the same subjects were undertaken. Findings show that the use of blood COPT method is advantageous over that of the stool examination in schistosomiasis surveys as its prescribed procedure is simple, specific and more sensitive. Moreover, the prevalence rate it determined was higher than that obtained by the stool examination in all three towns studied with underestimate prevalence from 9 to 19%.

Approximately 73 per cent of field rats were found infected with schistosomiasis as revealed by the finding of eggs in liver sections; 49 per cent showed eggs in sections of the intestines and about 13 per cent showed eggs in the stool. The fact that field rats frequent rice fields in quest of food and the frequency of their defecation should be considered seriously in trying to assess the role of field rats in the dissemination of the infection. Whereas it is true that humans, in schistosoma endemic areas in Leyte, are still the important source of infection, field rats could play the role of maintaining the infection in nature and may be responsible in contaminating areas where feces are never deposited.