Population genetics of Trypanosoma brucei and the epidemiology of human sleeping sickness in the Lambwe Valley, Kenya

Abstract

Numerical taxonomy was used to review isoenzyme variation in isolates of Trypanosoma brucei obtained from cattle, tsetse, humans and wildlife from the Lambwe Valley, Kenya. From isoenzyme information alone, it was possible to classify isolates as to source through the use of linear discriminant functions analysis, with an error rate of only 2% in humans, and 14% over all groups. Differentiation was mostly dependent on patterns in the enzymes ASAT, PEP1, and ICD. Parasites from non-human sources, especially tsetse, were characterized by high isoenzyme diversity, and many unique zymodemes. Observed frequencies of genotypes for ICD, ALAT, and ASAT did not agree with expected frequencies based on random mating of a diploid organism. Deviations were particularly large for tsetse isolates, and were mostly due to a deficiency of one homozygote. Cluster analysis revealed complex relationships among isolates, with patterns evolving through time. Major human zymodemes from the 1970s clustered together with most wildlife isolates from East Africa. This chronic human-wildlife transmission cycle was characterized by ASAT pattern I. Other, minor human zymodemes were associated with a human-cattle transmission cycle characterized by ASAT pattern VII. These original chronic transmission cycles appeared to change in 1980 with the appearance of two new zymodemes in humans. These zymodemes involved changes in ALAT and/or PGM to patterns typical of tsetse and cattle isolates. A resultant epidemic was halted with repeated aerial spraying of endosulfan in 1981. Since then, a variety of new zymodemes of unknown human infectivity have appeared. The origins of these changes are discussed in terms of genetic exchange in tsetse, adaptation to human and cattle transmission cycles, and selection resulting from chronic use of insecticides.

Evidence for clonal structure of natural populations of free-living amoebae of the genus Naegleria

“…This was demonstrated, for example, in the parasite Trypanosoma brucei (Mihok et al, 1990). However, such epidemic multiplications have never been reported for Naegleria populations except in the case of an abnormal and pronounced elevation of water temperature.…”

How clonal are bacteria?

“…However, Jenni et al (43) infected tsetse flies simultaneously with two strains of T. brucei and recovered recombinants, so it seems that sex does take place in the secondary host, even if it is hard to observe cytologically. Mihok et al (30) analyzed 321 strains of T. brucei from a valley in Kenya, isolated from tsetse flies, and from various primary hosts (humans, cattle, antelopes). The data, although less extensive than those for N. meningitidis, also suggest an epidemic population structure: sex is frequent, but occasionally a single ET becomes abundant.…”

Detection of T.b. rhodesiense Trypanosomes in Humans and Domestic Animals in South East Uganda by Amplification of Serum Resistance‐Associated Gene

“…Human pathogenic trypanosomes of the subspecies T. brucei are morphologically indistinguishable from those found only in other animals; and this has greatly hampered research on animal reservoirs. However, with the advent of biochemical and molecular markers some trypanosome stocks circulating in animals were shown to be similar to those found in man 1–5 . The importance of both wild and domestic animals in the epidemiology of T.b.…”