The largest study yet to be conducted on a free-ranging population of rhinos reveals that about one in every seven in the Kruger National Park (KNP) has been infected with Mycobacterium bovis (M. bovis) – the pathogen that causes bovine tuberculosis (BTB).
The study, conducted by Stellenbosch University’s (SU) Animal Tuberculosis Research Group, South African National Parks (SANParks) and the San Diego Zoo Wildlife Alliance in the US tested samples from 437 rhinos collected from 2016 to 2020 in KNP.
It revealed an estimated prevalence of M. bovis infection of 15.4% in black and white rhino populations in the park. While the research results are worrying, the evidence provided by the study is crucial to the effective conservation of the already vulnerable rhino population.
Added to this, scientists with the Animal TB Research Group, situated within SU’s Faculty of Medicine and Health Sciences, developed a novel diagnostic test to detect M. bovis in rhinos, which will greatly aid conservation efforts.
The researchers emphasised that the presence of infection did not mean the animals were diseased or dying. Prof Michele Miller, who leads the Animal TB Research Group, said their research showed that most rhinos could contain the infection if they were otherwise healthy.
“It can be compared to humans who are infected with Covid or have latent TB but are asymptomatic. The infected rhinos are harbouring the bacteria, but their immune system is keeping it in check.
“They are not losing weight or coughing and if you looked at a group of 400 rhinos, you wouldn’t be able to pick out those that are infected. They can live for years with infection if it is contained.”
Dr Peter Buss, senior veterinary manager in KNP’s Veterinary Wildlife Services, added that there was no evidence at this point to suggest TB would have any impact on the rhino population.
“The rhinos are being exposed to the organism, they are mounting an immune response, but they are not getting sick and dying from it. The same applies to other species. For example, we know we get TB in our lions and that individuals will die of the disease. But if you look at the population level of the disease, lions seem to be doing fine and their numbers have remained fairly static.”
According to the researchers, the distribution of M. bovis infection in KNP rhinos is similar to that reported for other species in the park. For example, a 1991-92 survey of buffaloes showed widespread BTB in the central and southern regions of the park, with individual herd prevalence of up to 67%.
A later study (2012-13) showed an overall infection prevalence of 44% in lions in the same areas. Such extensive infection is increasingly observed in species like warthogs, wild dogs and elephants, with cases identified in more than 15 species to date.
This suggests spillover of BTB is not a new occurrence and supports the need for ongoing BTB surveillance across species.
“While this pathogen may not appear to drastically impact the health of rhino individuals, the research has significant implications for conservation management decisions.
“For example, tuberculosis testing in KNP rhinos earmarked for translocation for conservation reasons can increase confidence of minimal risk to other individuals at their destinations,” said Rebecca Dwyer, lead author of the study and a PhD candidate in the Animal TB research team.
The study, published in the prestigious American scientific journal, Proceedings of the National Academy of Sciences, last week, identified proximity to buffalo herds (white rhinos) and sampling year (black rhinos) – which coincided with periods of drought – as risk factors for M. bovis infection.
A significant cluster of cases was detected near KNP’s southwestern border, although infection was widely distributed. The identified cluster is close to the KNP border with Mpumalanga, consisting primarily of farmland with livestock herds that have historically been implicated in spillover of M. bovis to wildlife in KNP, especially to buffaloes.
“With rhinos being threatened by poaching, habitat loss and drought, it is key to be able to translocate them to strongholds where they can be kept safe and to preserve their genetic diversity,” said Miller.
“But TB is a controlled veterinary disease, so once our research group found TB in Kruger rhinos in 2016, the department of agriculture, land reform and rural development imposed movement restrictions to prevent spreading the infection.”
Buss added: “Although it has been around for 60 to 70 years in Kruger, it would still be considered a relatively new disease. Because TB manifests so slowly, it is still expressing itself at a population level and we still need to reach some sort of equilibrium with the disease.”
KNP is the only national park where TB has been diagnosed in rhinos.