Immunity in trypanosomiasis

Extract

Success in immunizing rabbits, rats and sheep with dead trypanosomes depends on the method of killing trypanosomes, the frequency of inoculations, and the strain used for immunization. Positive results were obtained when trypanosomes were killed by formalin or by freezing and thawing five times. Negative results were obtained when trypanosomes were killed by 56° C. for half an hour.

Animals which received 10 doses of the mixture produced better results than those which received the same amount but only in 2 doses. An addition of Freund's adjuvant improved results, but 10 doses without an adjuvant were still better than 2 doses with an adjuvant. When trypanosomes were killed by 0·5% formalin, only an M variant of T. brucei, which was maintained by frequent passage in mice and was an antibody-sensitive variant, was able to produce in animals protective antibodies and resistance to a homologous ‘M’ variant, but not to an ‘R’ variant. On the other hand, if an ‘R’ variant of the same strain, which was passaged forty-eight times through rabbits and became resistant to antibodies, was killed by 0·5 % formalin and inoculated into animals, no antibodies and resistance could be demonstrated to a homologous ‘R’ variant and an ‘M’ variant.

Although it is possible to produce immunity in animals with dead trypanosomes further studies, particularly in the field, are necessary to find its practical application.