The resistance to human plasma of Trypanosoma brucei, T. rhodesiense and T. gambiense

Abstract
Tests were made in vivo of the sensitivity or resistance to human plasma of many strains of polymorphic trypanosomes. Five strains of T. gambiense from Nigeria were tested and all were highly resistant. Fifteen strains of T. rhodesiense (isolated from man in East Africa) were tested and they showed great variation in their degree of resistance from high resistance (five strains) to only subresistance (two strains). Forty strains of T. brucei (isolated from animals or tsetse flies) were tested; 20 were sensitive, nine were doubtful (probably sensitive) and 10 were subresistant (i.e., probably only one of a million trypanosomes in them was resistant). One strain (ETAT 10, isolated from tsetse flies) was highly resistant. During this work, tests were made on 14 strains of T. brucei (isolated from animals or fly) which were recorded as having been tested on human volunteers. Six of these strains were sensitive to human plasma and none had infected volunteers. Seven strains were subresistant, and three had infected volunteers. One strain was highly resistant and had infected a laboratory worker. For practical purposes it is advisable to consider that if a strain of polymorphic trypanosomes is plasmasensitive, it is probably not infective for man; if a strain is at all plasma-resistant it is potentially infective for man; and if a strain is highly resistant then it is almost certainly infective for man.

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