Epidemiology of Trypanosomiasis in Wildlife—Implications for Humans at the Wildlife Interface in Africa

Abstract

While both human and animal trypanosomiasis continue to present as major human and animal public health constraints globally, detailed analyses of trypanosome wildlife reservoir hosts remain sparse. African animal trypanosomiasis (AAT) affects both livestock and wildlife carrying a significant risk of spillover and cross-transmission of species and strains between populations. Increased human activity together with pressure on land resources is increasing wildlife–livestock–human infections. Increasing proximity between human settlements and grazing lands to wildlife reserves and game parks only serves to exacerbate zoonotic risk. Communities living and maintaining livestock on the fringes of wildlife-rich ecosystems require to have in place methods of vector control for prevention of AAT transmission and for the treatment of their livestock. Major Trypanosoma spp. include Trypanosoma brucei rhodesiense, Trypanosoma brucei gambiense, and Trypanosoma cruzi, pathogenic for humans, and Trypanosoma vivax, Trypanosoma congolense, Trypanosoma evansi, Trypanosoma brucei brucei, Trypanosoma dionisii, Trypanosoma thomasbancrofti, Trypanosma elephantis, Trypanosoma vegrandis, Trypanosoma copemani, Trypanosoma irwini, Trypanosoma copemani, Trypanosoma gilletti, Trypanosoma theileri, Trypanosoma godfreyi, Trypansoma simiae, and Trypanosoma (Megatrypanum) pestanai. Wildlife hosts for the trypansomatidae include subfamilies of Bovinae, Suidae, Pantherinae, Equidae, Alcephinae, Cercopithecinae, Crocodilinae, Pteropodidae, Peramelidae, Sigmodontidae, and Meliphagidae. Wildlife species are generally considered tolerant to trypanosome infection following centuries of coexistence of vectors and wildlife hosts. Tolerance is influenced by age, sex, species, and physiological condition and parasite challenge. Cyclic transmission through Glossina species occurs for T. congolense, T. simiae, T. vivax, T. brucei, and T. b. rhodesiense, T. b. gambiense, and within Reduviid bugs for T. cruzi. T. evansi is mechanically transmitted, and T. vixax is also commonly transmitted by biting flies including tsetse. Wildlife animal species serve as long-term reservoirs of infection, but the delicate acquired balance between trypanotolerance and trypanosome challenge can be disrupted by an increase in challenge and/or the introduction of new more virulent species into the ecosystem. There is a need to protect wildlife, animal, and human populations from the infectious consequences of encroachment to preserve and protect these populations. In this review, we explore the ecology and epidemiology of Trypanosoma spp. in wildlife.

An Update on African Trypanocide Pharmaceutics and Resistance

“…In humans, the disease is generally categorized based on the protozoan species, i.e., Chagas disease (American trypanosomiasis) and sleeping sickness (human African trypanosomiasis). Both forms of the disease are prevalent in low-income countries of America, Africa, and Asia and it is of major concern since it affects wildlife ( 2 ) and livestock such as equines (horses and camels), and large and small ruminants (i.e., bovines, ovines, and caprines) ( 3 ). This affects livestock productivity especially among horses, donkeys, camels, sheep, goats, and buffalo due to its associated economic burden ( 4 ).…”

Prevalence of Trypanosome Species in Cattle Near Ruma National Park, Lambwe Valley, Kenya: An Update From the Historical Focus for African Trypanosomosis

“…Similar to previous reports from Lambwe, the second-highest infections were of T. vivax (31.2%, 83/266) and after that, T. brucei brucei (27.4%, 73/266) ( 7 , 13 ). The role of cattle and wildlife in sustaining the sylvatic cycle of T. brucei rhodesiense , especially in wildlife–livestock interfaces, is well-established ( 6 , 11 , 38 – 40 ). In a survey on small ruminants and cattle in Ngorongoro conservation in Tanzania, Ruiz et al ( 39 ) reported that 2.1% of cattle had T. brucei rhodesiense .…”

“…The lack of explicit information for the prevalence of pathogens, especially in the wildlife-livestock-human interfaces, is a major drawback for effective control of AAT ( 11 ). Consequently, the recently defined progressive control pathway for AAT advocates for enhanced research to understand the risks of trypanosomosis to guide the selection of priority intervention areas as the first step toward effective control ( 12 ).…”

Parasite co-infection: an ecological, molecular and experimental perspective

“…With respect to trypanosomes, the potential for infection with multiple species is particularly high because these parasites have an unusually broad host range, allowing frequent interactions between species in diverse hosts. Reflecting this, a large number of studies in different regions have reported the co-circulation of T. brucei , T. congolense and T. vivax , and these have been detected both in surveyed livestock and game animals [ 10 ], as well as in trapped tsetse flies (e.g. [ 11 , 12 ]).…”