The animal trypanosomiases and their chemotherapy: a review

Abstract

Pathogenic animal trypanosomes affecting livestock have represented a major constraint to agricultural development in Africa for centuries, and their negative economic impact is increasing in South America and Asia. Chemotherapy and chemoprophylaxis represent the main means of control. However, research into new trypanocides has remained inadequate for decades, leading to a situation where the few compounds available are losing efficacy due to the emergence of drug-resistant parasites. In this review, we provide a comprehensive overview of the current options available for the treatment and prophylaxis of the animal trypanosomiases, with a special focus on the problem of resistance. The key issues surrounding the main economically important animal trypanosome species and the diseases they cause are also presented. As new investment becomes available to develop improved tools to control the animal trypanosomiases, we stress that efforts should be directed towards a better understanding of the biology of the relevant parasite species and strains, to identify new drug targets and interrogate resistance mechanisms.

Keywords: Trypanosoma brucei; Trypanosoma congolense; Trypanosoma vivax; animal trypanosomiases; drug resistance; veterinary trypanocide.

Fig. 1.

Morphological characteristics of the bloodstream form trypomastigote of the three most important livestock trypanosomes. T. brucei group trypanosomes (T. b. brucei, T. b. evansi, T. b. equiperdum) are morphologically indistinguishable (with the exception of the non-proliferative stumpy-form in T. b. brucei). The trypomastigote is the disease-relevant form and the target of therapy.

Fig. 2.

Countries where the most important livestock trypanosomes are present. Modified from (Auty et al. 2015), based on PubMed search and including countries where data were not available and parasite presence is inferred. To note that the real geographical distribution in some countries is limited (as, for example, for T. congolense in South Africa, Namibia and Botswana and for T. b. evansi in Russia). Cases of eradicated outbreaks of T. b. evansi in Europe (i.e. in France) are not indicated.

Fig. 3.

Phylogenetic tree based on SSU rRNA sequences from trypanosome species. Modified from (Cortez et al. 2006).