Survey of infections transmissible between baboons and humans, Cape Town, South Africa

The close contact between baboons and humans results in a high potential for the transmission of infectious diseases, from baboons to humans (zoonoses) and from humans to baboons (anthroponoses). Globally, disease transmission between humans and wildlife is occurring at an increasing rate, posing a substantial global threat to public health and biodiversity conservation. Although a study of baboon parasites in Kenya found none directly attributable to exposure to humans, the human parasite Trichuris trichiura has recently been identified in the Cape Peninsula baboon population; this finding represents the first evidence of likely anthroponotic infection of baboons. Diseases such as measles and tuberculosis are highly prevalent among the local human population and have the potential to pass to baboons. The risks for infectious disease transmission between baboons and humans remain unclear. The aim of this study was to determine which diseases are currently present in the Cape Peninsula baboon population to inform decisions relating to baboon management, welfare and conservation, and the health risk to local humans and baboons. Ethical approval was gained from the Royal Veterinary College Ethics and Welfare Committee.

The study provides evidence of the potential for cross-species trafficking of select pathogens. Widespread evidence of reactive or cross-reactive humoral immune responses to human pathogens was found in wild baboons. The detection of antibodies reactive or cross-reactive to HAV in 30% of baboons tested is a potential cause for concern. Because HAV is spread by the fecal–oral route, many opportunities might exist for direct and indirect transmission between baboons and humans; e.g., baboons frequent picnic sites and enter houses and cars in search of food. The frequency with which such contacts result in transmission of HAV should be investigated because of the potentially fatal consequences of human infection with HAV, particularly for immunocompromised persons such as those co-infected with HIV. Furthermore, as pathogens pass back and forth across species lines, the potential for changes in pathogenicity and host specificity exists, which can result in serious adverse effects on human and wildlife health.

The considerable variation in virus immunity among baboon troops warrants further study. The difference was particularly pronounced in the 2 most sampled troops, in which HAV antibody prevalence varied from 0% (0/8 baboons in the Tokai MT1 troop, in a forest) to 86% (6/7 baboons in the Da Gama troop, in an urban area). Future work should target these groups for more extensive sampling (ideally, all baboons should be sampled) to more accurately determine the prevalence of infection and investigate risk factors for virus exposure. A suitable hypothesis for testing would be that zoonotic infection prevalence in baboons is positively correlated with the proportion of urban land in their habitat.

The results of this study suggest that baboons on the Cape Peninsula pose a low but potential risk for transmitting zoonoses and that they might be at risk from anthroponoses. The findings should not be interpreted as definitively showing baboon exposure to human viruses because the serologic tests did not distinguish between human and baboon variants of the viruses and some cross-reactivity may have occurred. Virus isolation would be needed to determine the virus types. Nonetheless, there is ample evidence that disease of human origin can be devastating for primate populations. Further research is required on the Cape Peninsula to quantify the incidence of infections in baboons and humans, to examine the variation in levels of infection among baboon troops, and to measure the frequency of contact between species. Estimating the probability of cross-species disease transmission is challenging, but this information would be of tremendous use in informing baboon management plans with the aim of reducing the risks for infectious disease in humans and baboons. Dr Drewe is a veterinary epidemiologist at the Royal Veterinary College in London. He is particularly interested in infectious diseases that are transmitted between wildlife, humans, and domestic animals and in identifying effective management strategies for such diseases.

Emerging Infectious Diseases
February 21, 2012

Original web page at Emerging Infectious Diseases