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.