Infectivity and virulence in a serodeme of Trypanosoma vivax

The course of infection by a mouse-adapted Trypanosoma vivax was studied. Serological variants were isolated from sheep and their infectivity and virulence were studied in mice and sheep. Isolates obtained in the early stage of the infection were highly virulent while isolates obtained at the terminal stage of the infection were found to be extremely virulent in both mice and sheep. Trypanosoma vivax organisms isolated in between these series of parasitaemias were of low to moderate virulence in both groups of animals. The degree of virulence exhibited by each isolate was closely related to the viability of the organisms. The success of making clones was equally found to be related to the virulence of the isolates.