Test developed to identify bovine TB in wild rhinos

Dr Josephine Chileshe.
Her curiosity about understanding diseases – in animals and humans – has led to Dr Josephine Chileshe developing a novel tool to help diagnose tuberculosis (TB) in rhinos, for which she received a doctoral degree from Stellenbosch University (SU) this week.
 
“As an animal health technician I’m interested in both animals and disease. My long-term interest is prevention and control strategies for zoonotic diseases of which bovine TB is one. If we can diagnose diseases in animals before they reach humans, we will make a huge impact,” said Chileshe, who did her PhD with the Animal TB Research Group at SU’s Faculty of Medicine and Health Sciences.
 
Chileshe’s PhD dissertation, entitled Identification of immunological biomarkers for detection of Mycobacterium bovis infection in African rhinoceros, focused on the detection of biomarkers and their diagnostic use for Mycobacterium bovis infection in African rhinoceros. The bacteria Mycobacterium bovis causes bovine TB, which usually affect animals such as cattle, but can also infect and cause disease in all mammals, including humans.
 
Although we have known about TB in rhinos since the 19 th century, it had only been reported in captive rhinos. Bovine TB is endemic in many animal species across South Africa, including animals in the Kruger National Park, where this work was done. Finding bovine TB in rhinos that had died from other causes made it clear that it can infect wild rhinos.
 
“With poaching and decreasing rhino numbers, it is key to be able to translocate these animals to strongholds where we can keep them safe and preserve their genetic diversity. TB is a controlled disease so once it was found in Kruger, the Department of Agriculture imposed a quarantine and we were not allowed to move rhinos,” explained Prof Michele Miller, who leads the Animal TB Research Group and supervised Chileshe’s dissertation. “The solution was to come up with a test to identify infected animals before they are moved to prevent disease transmission.”
 
A blood test means it’s possible to identify TB in living animals and also to get an idea of its prevalence – at the moment it is believed that about 5% of the Kruger population has been exposed. “Chileshe’s thesis explored the best way of identifying infected animals – not so much for the health of the individual animals because we don’t think that TB is killing rhinos – but to prevent the spread to other susceptible populations. These findings are significant contributions to knowledge and management of animal TB,” said Miller.
 
Chileshe developed and validated an interferon-gamma release assay (a blood test used to detect TB infection), and characterised cytokine gene-expression assays that can be used to distinguish between Mycobacterium bovis-infected and uninfected rhinos.
 
She explained that current knowledge on biomarkers in other species including humans was the starting point. “We looked at biomarkers identified in other species and if we could identify them in rhino. Interferon gamma has been well studied in humans. We were able to identify a test that recognised that marker in the rhino. Using real-time gene expression we were also able to identify Interferon gamma-inducible protein 10 (IP10). We identified six out of 84 markers in one screening test. The more markers you identify, the better.”
 
In field conditions it is also important to use available reagents and test kits for easy reproducibility. Various kits were tested to come up with a system that consistently detected the biomarkers.
 
“Obviously in the wild animals can’t be that closely monitoring,” said Chileshe. “Earlier indication of infection would allow us to act proactively. But testing is the tip of the iceberg, there are still many unknowns.” She pointed to the need for more validation of testing in larger cohorts; understanding the mechanism behind IP10 production and whether it’s indicative of disease in rhinos; the evaluation of more cytokines as biomarkers, and, understanding immunology in bovine TB infection.
 
For now, her interest is moving to humans. “I will be doing a postdoc at the University of the Free State on developing a point-of-care diagnostic tool for Covid-19,” she said.
 
“As we have learned from Covid-19 many diseases cross species barriers,” added Miller. “We can’t have a species-centric focus but must look at diseases at the interfaces between humans, livestock, pets and wild animals and how we can accurately predict infections. We will never win the battle by trying to control disease in just one species.”
 
This work was done in collaboration with South African National Parks, the Department of Agriculture and state veterinarians.
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