Interference in the Establishment of Superinfections with Trypanosoma congolense in Cattle

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Abstract
To examine the influence of an established infection on subsequent challenge with another unrelated trypanosome serodeme, cattle were subjected to 2 challenges, 5-6 wk apart, with unrelated isolates of T. congolense. The primary infection inhibited the establishment of the 2nd infection despite the initial absence of detectable antibody to the trypanosomes used for the 2nd challenge. This was true whether the 2nd challenge consisted of bloodstream forms of the parasite or metacyclics from infected Glossina morsitans morsitans. Rechallenge with bloodstream forms resulted in a slight antibody response, which was only detectable by immunofluorescence and was much less than in the challenge controls. Although animals subjected to the 2nd challenge by tsetse flies showed no appreciable increase in parsitemia and, in most instances, no chance reaction at the site where the tsetse bit, they developed readily detectable neutralizing antibody to the metacyclic trypanosomes. That this interference effect was not the result of specific immunity and required an active infection was confirmed by the finding that when infected animals were treated with Berenil prior to rechallenge, they were fully susceptible to the infection.

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