SKUKUZA – Tuberculosis (TB) is usually considered a human problem. It is seldom taken notice of when present in animals. Due to groundbreaking research by animal experts, the scientific management of this threat to wildlife health is gaining ground.
Rhombus Media spoke to an expert on TB in animals for World Tuberculosis Day 2019, 24 March 2019.
“Wildlife TB has significant consequences, especially for threatened and endangered species. We just do not know enough about the disease. Research is crucial for formulating strategies to prevent and manage the impact thereof,” says Professor Michele Miller, who is on the faculty of the Department of Biomedical Science at the Stellenbosch University Faculty of Medicine and Health Sciences.
She has done research with a team of experts and postgraduate students as well as the Veterinary Wildlife Services staff of the KNP on the disease in Kruger National Park (KNP) and Hluhluwe-iMfolozi Park animals since 2014.
Miller is also the National Research Foundation’s South African Research Chair in Animal TB which functions as part of the Department of Science and Technology–National Research Foundation Centre of Excellence for Biomedical TB Research and South African Medical Research Council. She holds a B.S. in Physics and Zoology, an M.S. and PhD in Veterinary Science, D.V.M., from the University of Wisconsin, and M.P.H. from University of Florida. For eleven years, she has served at Disney’s Animal Programs in Buena Vista, FL, where she was Veterinary Operations Manager and staff veterinarian.
One of the recent findings (2017) of Miller and her research team was that more than 40 per cent of the Kruger Park lions in a test group tested positive for the disease even though at the time the disease might not have developed in some of them.
The first noted case of TB in lions in the KNP was in 1996.
Blood samples are taken after lions are chemically immobilised, blood taken from the veins in their necks or legs and sent to the laboratory in the KNP to be processed.
Older lions and males mostly infected
The research shows that older lions, male lions and immune-compromised lions may be more prone to be infected. The southern part of the KNP has the most infected lions. The Crocodile Bridge pride had the highest prevalence of the disease in this study.
“Since the Kruger Park is one of the remaining strongholds for lions in Southern Africa, this scenario is extremely worrying,” says Miller.
She noted that researchers do not have good evidence to prove how the disease progresses in lions and pointed out that some of these signs included elbow swelling and non-specific symptoms like scruffy coats, weight loss, and bone infections.
“We also do not know and understand the impact of TB on conservation in a park like the KNP. With the lions, the loss of an apex predator will have a detrimental effect on the ecosystem. We need a much longer period to really research this in depth.”
TB treatment in animals not a realistic option
Currently, there is no available treatment of TB in wild animals.
“Treatment has been attempted in some zoo animals, but this is complicated by the lack of information on effective drugs, doses and duration of treatment. The drugs used are the same as those in humans and require daily treatment for one to two years, so it is not realistic for wildlife,” says Miller.
Her concern is that infected wildlife can serve as a source of infection for other species, including humans that may have contact.
“Another complication is that TB is a controlled disease in animals and regulated by the Department of Agriculture, Forestry, and Fisheries (DAFF), which would need to approve any treatment. By the time most wildlife is found with TB, the disease is also advanced and not realistically treatable.”
Test results were possible due to a new molecular technique that Miller and her team developed for detecting infection.
Transmitting the real danger
She emphasises not only with lions but that the long-term consequences of all wildlife TB in South Africa are unknown.
“Being infected may have an influence on the hunting skills of the lions as well as the pride. Infected individuals also present a risk of transmitting TB,” says Miller.
Test results were possible due to a new molecular technique that Miller and her team developed for detecting infection. Dr Tashnica Sylvester, then a doctoral student at SU’s faculty of medicine and health sciences, did her studies for her PhD on the development of the test.
Sylvester was part of the research group that developed a test to diagnose TB in lions, using a single blood sample. Previously, a capture team captured a lion twice in three days to perform a TB skin test.
With the new test, it is only necessary to capture the animal once.
Miller pointed out that since no single test is perfect, additional tests continue to be investigated that could be used to increase confidence in the diagnosis of infection.
“We are also comparing the strains of the TB bacteria, Mycobacterium bovis, in lions with other species to determine the potential source of infection. For example, we know that buffalo with TB can infect lions but can infected warthogs and antelope also be a source?”
Miller says the problem with tuberculosis in wildlife is that the animals often do not show the typical signs of disease such as weight loss, loss of condition and lethargy until the disease is advanced.
In 2009, a workshop was conducted to model the impact of TB on lion populations in the KNP. Predictions covering the next 50 years showed that the illness was likely to cause an overall decrease in the lion population (a 35–75 per cent decline in the then current population) before stabilising.
TB not only a threat to KNP lions
Researchers have identified more than 20 wildlife species infected with tuberculosis including leopards, cheetahs, wild dogs, rhinoceros, greater kudu, and warthogs.
Studies have shown that animals in close contact with each other can transmit respiratory TB through the air (probably in buffalos), grooming (baboons) or bites. Tuberculosis found in other parts of the body can be contracted when carnivorous animals eat diseased meat.
Animals can pass on a different, but a related strain of TB usually present in people, caused by the bacterium Mycobacterium bovis, to humans through airborne droplets or products such as undercooked meat or unpasteurised milk.
The disease can spread further if other animals eat the carcass of the infected animal. Infected individuals may shed bacteria for long periods without apparent evidence of disease, resulting in transmission through direct contact or contamination of the environment. Mud baths can lead to animals picking up the bacteria if infected animals have contaminated the area.
As the disease advances, animals may experience decreased milk production and fertility, loss of body condition and coughing or other respiratory signs.
How the disease presents also depends on the species.
TB presents a serious threat to the conservation of this keystone species
TB recently found in KNP rhinos
During their 2016-2017 examinations of rhinos (35 white and five black), Miller and her team of researchers discovered that six of the white rhinos were infected. This was during a severe drought in the Lowveld.
“The disease is a controlled disease by DAFF which means animals identified as infected cannot be relocated. With rhinos, this presents a serious challenge. They sometimes need to be removed to more secure locations to prevent poaching.”
Around the world, rhinos in zoos have been diagnosed with TB, both human and bovine strains.
“Although this showed that these species are susceptible, we still don’t understand how they become infected. One of the ideas is that they may pick up bacteria in a contaminated environment. A key question that we are exploring is whether infected rhinos can transmit the bacteria, especially if they are stressed by translocation since this could threaten not only the individual but a population,” says Miller.
What about elephants?
Elephants will not necessarily show clinical signs for years although infected. If they do show signs, it might be similar to those of humans like weight loss.
Miller and her team recently published a paper on the first case of human tuberculosis found in an elephant in the KNP. A study is underway to screen elephants for tuberculosis (TB) with the human and bovine strains at the KNP since 2017 after the disease was detected in this elephant.
Miller said that active surveillance, detection before the disease is widely spread and identifying potential sources are important parts of any management plan to combat TB in animals.
“Sometimes a few difficult decisions need to be taken to secure a healthy future for the conservation of animals on the whole. Since we often find TB in wildlife only once the individual has advanced disease, the best decision for that individual’s welfare is to euthanize.”
Once the disease has been detected in a wildlife population, it is often difficult to control since it may have been years that the infection was present before it was discovered.
“The medical, veterinary, and wildlife communities have been struggling to address TB for decades, with some progress on our understanding and management, however, due to the chronic insidious nature and complexities surrounding this disease, we will not likely eliminate this threat to wildlife in the near future.”
Photographs of lions: Supplied by Prof. Miller
Rhino photograph: Elize Parker