Buffaloes doing OK with TB, now elephants are a worry

The Citizen recently sat down with South African National Parks’ disease ecology scientist Dr Danny Govender to establish the state of play of tuberculosis (TB) in the Kruger National Park which has a long history of affecting buffaloes, more recently lions and now elephants.

Tuberculosis is a one-size-fits-all disease, with strains having crossed the line between species.

In March, it was announced tests were being done to establish the spread of the human strain within African elephants.

“The elephant TB is quite different to what we’ve been having historically,” says Govender, general manager of the savanna-arid node for Scientific Services based in Skukuza. “… it has been diagnosed in zoos for a long time in mega herbivores such as rhino and elephant.”

Is Kruger a hotbed of diseased and dying animals? Yes, and no.

In the 1990-91 drought, the disease was spread by compromised animals who coughed all over the grasslands and were eaten by predators and scavengers, and in the late 1990s, the disease began to present much more often. Up to 20% of the buffaloes in the south of the park was estimated to be affected and over the years it made its way north until 2012, when the last large-scale TB count was done.

The disease levelled off, leaving a five to 10% prevalence and a 30 to 35% prevalence in the south, Govender says.

A count had not been done since the last drought, but the survival rates seem to suggest there was a high level of resistance. There might be a small chance the disease could burn itself out, or a survival-of-the-fittest stance should be taken.

This was where ecosystem management came into play, to manage numbers by controlling water access, which allowed the strongest animals to survive. It appears to have worked, with numbers still higher than the culling-maintained herds of the 1990s after the drought. Then, the spillover hosts, such as lions, other predators and scavengers, became of concern.

Govender says a study by former state veterinarian Dr Dewalt Keet to see if prides were being destabilised, found the south of the park more susceptible – mainly due to prey density being higher, which had the knock-on effect of a high turnover in lion hierarchy due to more competition for resources.

A later study confirmed the findings, but found the destabilisation had little to do with the disease itself.

“Right now, we’re keeping tabs on the system,” Govender says. “We need to reflect on the effects of the drought, to see the level of resistance which came through, go through another wet period to see how the animal numbers are doing, and then another drought so we can build a better picture of what the longterm effects of the situation is.”

She noted that in zoos, animals were generally diagnosed with human TB, usually from contact with keepers, and would develop chronic TB which killed them.

“By the time the disease is diagnosed, it has usually progressed quite far. Treatment consists of six different kinds of antibiotic,” says Govender.

Because dosage depends on weight, an elephant needs kilograms of antibiotics over six months, which is expensive.

“The problem with vaccines is that often animals have been primed by being exposed to various strains of TB and the vaccine doesn’t elicit the desired, strong, response.”

This was particularly common to animals which shared mud baths.

INFO

Ancient disease

• In her 2015 inaugural lecture, “Tuberculosis in South African wildlife: why is it important”, Professor Michele A Miller of the department of biomedical sciences at the Stellenbosch University faculty of medicine and health sciences, referred to TB as an “ancient” disease, having been found in the bones of prehistoric mastodons.
• The spread of bovine TB to additional species was documented in the Kruger National Park from the early 1990s.
• “These species included lions, cheetahs, greater kudus, baboons, leopards, warthogs and banded mongooses,” said Miller.
• She noted the first case of bovine TB was diagnosed in a black rhinoceros in 1970, while buffalo were found to be infected in 1986 and lions, greater kudus and bush pigs have been infected since the 1990s.
• Miller is currently conducting the research into the spread of TB in elephants.

– amandaw@citizen.co.za

For more news your way, download The Citizen’s app for iOS and Android.