Cape Town - About one in every seven rhinos in the Kruger National Park (KNP) showed evidence that they had been infected with Mycobacterium bovis (M. bovis) – the pathogen that causes bovine tuberculosis (bTB).
This is according to the largest study ever to be conducted on a free-ranging population of rhinoceros, undertaken by Stellenbosch University’s (SU) Animal Tuberculosis Research Group, South African National Parks (SANParks) and the San Diego Zoo Wildlife Alliance, US.
The experts tested samples of 437 rhinoceros collected from 2016 to 2020 in KNP and found 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 emphasise that the presence of infection does not mean that the animals are diseased or dying.
Professor Michele Miller, who leads the Animal TB Research Group and is the National Research Foundation (NRF) South African Research chairperson in Animal TB, said their research showed that most of the rhinos can contain the infection if they are otherwise healthy.
“It can be compared to humans who are infected with Covid-19 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 potentially live for years with infection if it is contained,” she said.
Dr Peter Buss, veterinary senior manager in KNP’s Veterinary Wildlife Services, said there is no evidence at this point to suggest that TB will 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 that 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.”
The authors said TB is prevalent in at least 15 other species in KNP, but that their research has significant positive implications for SANParks’ rhino conservation and management strategy.
“While this pathogen may not appear to drastically impact the health of rhinoceros individuals, the research has significant implications for conservation management decisions. For example, tuberculosis testing in KNP rhinoceros that are earmarked for translocation for conservation reasons can increase confidence of minimal risk to other susceptible individuals at their destinations,” explained Rebecca Dwyer, lead author of the study and a PhD candidate in the Animal TB research team.
The study, published in the American scientific journal “PNAS” (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 south-western border, although infection was widely distributed. The identified cluster is close to the KNP border with the surrounding Mpumalanga province, consisting primarily of farmland with livestock herds that have historically been implicated in spillover of M. bovis to wildlife in KNP, especially to buffalo.
“With South African 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, in partnership with SANParks, found TB in Kruger rhinos in 2016, the Department of Agriculture, Land Reform and Rural Development (DALRRD) imposed movement restrictions to prevent spreading the infection to other populations.”
These restrictions created a barrier to the movement of rhinos to other national or private reserves and has a significant impact on the conservation of the species, as KNP has historically been an important population source of rhinoceros for other conservation strongholds in South Africa and other African countries.
The solution was to come up with a test to identify infected animals before they were moved to prevent disease transmission.
According to Dr Wynand Goosen, Wellcome International Training fellow in the Animal TB Research Group, the screening test that was used in their KNP study was validated by the Animal TB Research Group in 2019 and was recently approved by DALRRD for use in KNP rhinos.
A management strategy involving a quarantine protocol and testing schedule was devised in collaboration with SANParks and has been approved.
“Should we now wish to start moving rhinos out of Kruger, we have that option to quarantine them and test them, and then send them out,” said Buss.
Although people can become infected with bTB, it usually only happens when they regularly handle infected (uncooked) animal organs or drink unpasteurised milk. Unlike diseases such as Covid-19, people need close prolonged contact to get TB and won’t contract it from visiting KNP, stressed Miller.