Trypanosoma brucei rhodesiense infection in vervet monkeys. II. Provocation of the encephalitic late phase by treatment of infected monkeys.

Four out of 8 monkeys infected with Trypanosoma rhodesiense and treated with trypanocidal drugs at various intervals after infection (days 55-58, days 62-65, day 68) developed encephalitis. In 2 of these animals, killed 2 weeks after treatment, the encephalitis presenting was incipient; the other 2 monkeys died as a result of severe encephalitis a little more than 2 and 3 months after treatment, respectively. At the time of treatment, the animals revealed a parasitization of the CSF, but there were no clinical or neurological signs of any involvement of the central nervous system. The observations confirm observations made in human trypanosomiasis, and in experiments on rodents, which indicate that the encephalitic late phase may result from inadequate treatment. These observations may indicate that the encephalitis of the late phase may be methodologically provoked by infection and subliminal treatment after parasitization of the CSF, and that this procedure may be more promising of success than the method of infection only, as a method for the production of an animal model of the encephalitic late phase.