The Molecular Basis of Livestock Disease as Illustrated by African Trypanosomiasis

Abstract

African trypanosomes are protozoan parasites, most species of which are transmitted by tsetse flies. They reside in the mammalian bloodstream and evade the immune system by periodically switching the major protein on their surface — a phenomenon called antigenic variation, mediated by gene rearrangements in the trypanosome genome. The trypanosomes eventually enter the central nervous system and cause a fatal disease, commonly called ngana in domestic cattle and sleeping sickness in humans. Two sub-species of Trypanosoma brucei infect humans (T. b. rhodesiense and T. b. gambiense) and one sub-species does not survive in humans (T. b. brucei) because it is lysed by the human-specific serum protein, apolipoprotein L-I. Wild animals in Africa have other (less well understood) molecular mechanisms of suppressing the number of African trypanosomes in the blood, and some indigenous breeds of African cattle also display a partial “trypanotolerance” whose genetic loci have recently been mapped.