Investigation of shared antigens between schistosoma mansoni and the intermediate host, biomphalaria pfeifferi

Abstract

schistosomiasis is a major health problem especially in the developing countries within the tropics. The search for an effective vaccine has however been frustrated by two main contraints namely, the antigenic complexity of the parasite and the difficulty of producing adequate research material from the tiny parasite stages. These two problem would be overcome if an alternative source of immunising antigens could be found. The present work involved a search for such antigens from the snail vector of Schistosoma mansoni, Biomphalaria pfeifferi. Antigen fractions from various parts of the vector snail were isolated using conventional immunochemical techniques. Similarly antigens were obtained from different stages of S- mansoni using homogenisation and centrifugation techinques. A battery of antisera of all the antigenic preparations were raised in the rabbits and antigenic cross-reactivity was investigated using gel diffusion technique. The potency of each antisera was ascertained by reacting it with its homologous antigen. The results obtained clearly indicate that both the digestive gland and the alimentary canal of the snail vector, possess antigens which cross-react with S- mansoni egg antigens. No such cross-reactivity was detected between the foot of ofeifferi and any of the stages of S- mansoni. Similarly, no shared antigens were detected between the digestive gland of the non-vector snail Bulinus africunus and S- mansoni. In order to establish their immunising potential and the degree of protection, the snail antigens were used to immunise groups of hamsters and the numbers of adults worms recovered from the immunised groups were compared with those from control groups. The results were statistically significant and indicated that the best protection was achieved using antigenic preparations from either digestive gland or the alimentary canal of the snail. The percentage worm reduction for the digestive gland and its two antigenic fractions were 28.5%, 65.0% and 52.4% respectively, while that of the alimentary canal and its two antigenic fractions were 45.6%, 52.6% and 56.6% respectively. The least worm reduction was obtained from the foot and its two antigenic fractions. These were 12.3%, 26.2% and 24.6% respectively. The results therefore, of both antigenic crossreactivity and immunisation experiments strongly suggest the presence of shared antigens between Schistosoma mansoni eggs and the intermediate host, Biomphalaria pfeifferi. These results agree with those obtained by other workers. Lehman and Ruahini (1982) obtained 63.9% protection against ~ mansoni when they immunised mice using crude extracts of the whole snail, pfeifferi. Similarly Carlos et ale (1985) found out that the digestive gland of S- mansoni's Puerto Rican vector, Biomphalaria grabrata shared 2.8% of its antigens with S-mansoni. suggestion are made for further research work in trying to develop a vaccine against schistosomiasis