Investigation on immunity induced by Schistosoma spindale against S. mekongi in experimental mice

An investigation on immunity induced by Schistosoma spindale cercariae (cattle and swamp buffalo schistosome) against S. mekongi (human schistosome) was conducted in Swiss albino mice. The studies comprised the development patterns of homologous immunity of S. spindale and heterologous immunity induced by S. spindale against S. mekongi. The development pattern of homologous immunity was studied in mice with an immunization of 100 S. spindale cercariae. At one week intervals, between 2 to 16 weeks after immunization, they were each challenged with 500 S. spindale cercariae. Significant homologous immunity, as judged by lung recovery assay five days after challenge, occurred from week 5 to week 16 with week 8 giving the highest homologous immunity (68.1% of schistosomular reduction). Using the above information mice, with an eight-week immunization period of 100 S. spindale cercariae, were tested for resistance to heterologous S. mekongi infection. The criteria used to evaluate their immune status was schistosomular lung recovery, daily egg output, worm recovery and tissue egg count. The results showed that mice immunized with S. spindale cercariae could develop heterologous immunity against S. mekongi infection. Manifestation of immunity was demonstrated by significant reduction in mean schistosomular recovery (31.4%), in mean daily egg output per female worm (16.7%), in mean worm recovery (64.2%) and in mean egg deposition in the liver tissue and intestines per female worm (37.05%).