Enzyme electrophoresis in characterizing the causative organism of Gambian trypanosomiasis

The identification by isoenzyme patterns of two distinct strain-groups of Trypanosoma cruzi, circulating independently in a rural area of Brazil

Culture forms of 17 Trypanosoma cruzi stocks, primarily isolated from a rural area of endemic Chagas disease at São Felipe, Bahia, Brazil, were compared by the electrophoretic patterns of six enzymes: aspartate aminotransferase, alanine aminotransferase, glucose-6-phosphate dehydrogenase, malate dehydrogenase (decarb-oxylating) (NADP+), glucosephosphate isomerase and phosphoglucomutase. Two markedly distinct combinations of isoenzyme patterns were seen, justifying the arrangement of the 17 stocks into two strain-groups, each of which was enzymically homogeneous. One combination was characteristic of the 11 domestic stocks of T. cruzi derived from both human infections and domiciliated animals; the second was characteristic of the six sylvatic stocks derived from opossums and a sylvatic triatomine species. The enzyme patterns were independent of the original host and the type of culture medium used. Distinction of the two strain-groups accords with epidemiological evidence that the domestic and sylvatic transmission cycles in São Felipe do not overlap. It is suggested that the diverse enzyme characters of the two strain-groups circulating in São Felipe reflect diverse origins; the domestic form of T. cruzi probably invaded the area from the south of Brazil with the domestic triatomine vector, Panstrongylus megistus.

The resistance to human plasma of Trypanosoma brucei, T. rhodesiense and T. gambiense. II. Survey of strains from East Africa and Nigeria

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 stains 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.