Spillover risks of emerging (zoonotic) diseases at the human-livestock-wildlife interface: the case of bovine tuberculosis in cattle around Akagera National Park in Rwanda.

Abstract

Worldwide, the contact between wildlife, domestic animals and humans increases, resulting in increased risk of disease spillover from one species to the next. This is especially a big problem in many sub-Saharan African countries, like Rwanda, where many high-impact potentially zoonotic diseases are present, like bovine tuberculosis (bTB). We use bTB in Rwanda as a case study to map the many problems and challenges in characterising disease spill-over in such a high-risk setting. Bovine tuberculosis is an important zoonotic disease in cattle, that has a wide host-range in wildlife and is underdiagnosed in many countries. We conducted a study at the human-livestock-wildlife interface in the Kayonza district in Rwanda, next to the Akagera National Park (NP), where the bTB maintenance host, the African buffalo, and many potential spillover-host-species live. We tested 150 cattle in 15 farms for bovine tuberculosis, using the single intradermal comparative cervical tuberculin (SICCT) test, and did interviews to determine the presence of risk factors. The farms were all within 2.5 km from the fence of the park and divided over three sectors. We found an animal-based apparent prevalence of 2% (95% CI: 0.52-6.2) and a herd apparent prevalence of 20% (95% CI: 5.3-49%), for cut-off value CIDT >4 mm. Risk factors for bTB present in this area are between-herd movements, shared water points, introduction of new animals, mixed rearing cattle and goats, nutritional stress, old age and contact with wildlife reservoirs. No statistically significant correlations were found between these risk factors and infection based on this dataset. Bovine tuberculosis poses a risk for public health, due to the consumption of raw milk on 40% of the test farms and close contact with animals. Other important cattle diseases that are present in the research area are trypanosomiasis, tick-borne diseases (especially East Coast fever or theileriosis and anaplasmosis), brucellosis, foot and mouth disease, Rift Valley fever and anthrax, among others. Through the questionnaires we showed that many wildlife species, from in- and outside of the park, visit the farms and have direct contact with the domestic animals. Among these are buffaloes, different antelope species, primates, hippopotami, warthogs and carnivores. In addition, there is an abundance of vector species like tsetse flies and ticks. These data together make spillover of diseases between domestic animals and wildlife highly likely. We recommend to further investigate the risk of bovine tuberculosis and other high-impact diseases at the domestic-wildlife interface near Akagera NP, by doing targeted disease monitoring in domestic animals and in wildlife, especially in buffaloes as they play an important role in diseases like bTB, brucellosis, tick-borne diseases and trypanosomiasis. One Health collaboration of different stakeholders is key in effectively protecting wildlife, humans and domestic animals.