On the persistence of human serum resistance and isoenzyme patterns of Trypanozoon in experimentally infected pigs.

'Mini-pigs' were infected with salivarian Trypanozoon clones to examine the persistence and stability of the human serum resistance [Blood Incubation Infectivity Test (BIIT)] and isoenzyme characteristics during infection in a new host. A stock regarded as Trypanosoma brucei, derived from a domestic pig in the Ivory Coast, retained its BIIT negative (serum sensitive), alanine aminotransferase (ALAT) and peptidase 2 (PEP 2) characteristics throughout 343 days of infection in pigs. Similarly there was no change in the BIIT positive (serum resistant) and different ALAT and PEP characteristics of a human isolate from the same area, and regarded as T. b. gambiense, during 154 days before the infection became undetectable. In mixed infections of the two clones in pigs, trypanosomes which were not treated with human serum and inoculated into Mastomys natalensis invariably displayed the 'T. b. brucei' characteristics. However, simultaneous inoculations of trypanosomes treated with human serum into M. natalensis always displayed the characteristics of the T. b. gambiense. Thus, in mixed infections, in which 'T. b. brucei' predominated, the minority 'T. b. gambiense' population was recoverable after treatment with human serum by subinoculation into Mastomys.