Serological investigations in an area of endemic filariasis due to Wuchereria bancrofti and Acanthocheilonema perstans in Gambia, West Africa

1. (1) The complement-fixation test for filariasis was applied to 247 sera in Gambia, West Africa, where there is a high incidence of W. bancrofti and A. perstans. 2. (2) The antigen employed was an alcoholic extract of dried D. immitis worms. When this antigen was tested in Hamburg against 55 sera from persons who had never left Europe, no false positive reactions were obtained. 3. (3) In Gambia, out of 51 persons with microfilariae of W. bancrofti alone, 57 per cent. gave a positive reaction. Three possible explanations are given for the negative reactions in the remaining 43 per cent. of cases. These are 1. (a) That as the antigen employed was not homologous it failed in some cases to give an optimal reaction with the antibodies present. 2. (b) That free antibodies might be absent periodically from the blood if they were adsorbed on to the microfilariae, or neutralized by an antigenic fluid from the adult worms, or if there was damage to the reticulo-endothelial system by metabolic products of the parasites. 3. (c) That as the parasites are so well adapted to their host, there is sometimes a poor level of production of antibodies. 4. (4) Of 24 persons with microfilariae of A. perstans alone, 25 per cent. gave a positive reaction. 5. (5) Of 13 persons with both microfilariae of W. bancrofti and A. perstans, 23 per cent. gave a positive reaction. 6. (6) Of 159 persons who lived in the endemic area studied, but had no microfilariae in the blood, 33 per cent. gave a positive reaction. 7. (7) Comparison is made between the results obtained in the present investigations and those reported by other observers.