Characterization of stocks ofTrypanosoma vivax

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Abstract
The antigenic relationships of seven stocks of Trypanosoma vivax from different geographical areas were compared by immune lysis, passive protection and crossed immunoelectrophoresis. Sera from calves infected with T. vivax were titrated against trypanosome populations isolated early in infection by the immune lysis test. The results showed that three stocks isolated from one area of Nigeria were closely related and had antigens in common with stocks from other areas. Sera from cattle naturally infected with trypanosomes in Zambia contained lytic antibody to three Nigerian and one East African stock. Lytic antibody to African stocks was not detected in the sera of calves infected with a stock of South American origin. The detection of inter- and intra-area cross-reactions suggest that there may be a limited number of antigenic types in nature. Sera from five selected calves which contained lytic antibody to homologous and heterologous stocks were injected into mice. Subsequent challenge showed that the injection gave complete protection or produced a prolonged prepatent period to the homologous stock. Cross-protection was also observed in three stocks originally isolated from the same area. Crossed immunoelectrophoresis demonstrated that all the stocks had a similar antigenic structure except for one component which was only present in three stocks. The high resolution of this technique suggests that it could be useful in the characterization of stocks of trypanosomes.