Effect of Feline AIDS and TB on KNP lions

Melissa Wray, Kruger Park Times

Mufasa. Photo © G & J Burgess 2004.

KNP - About 2000 lions roam the Kruger National Park. What effect is feline AIDS and Tuberculosis having on these lions? Melissa Wray reports.

Tests on lions in the Kruger National Park (KNP) have shown that both antibodies to the virus that causes feline Aids (Feline immunodeficiency virus or FIV) and the bacterium (Mycobacterium bovis) that causes bovine tuberculosis are present in the lion population.

Feline Aids

According to Dr Roy Bengis, a state veterinarian, although FIV antibodies have been detected in KNP lions since the late 1980s, the disease does not appear to have had any detectable health implications in this lion population. This is reiterated by Professor Moritz van Vuuren, a virology professor from Onderstepoort, part of the University of Pretoria. He has been working on isolating and identifying the virus for the last five years. He said, "In free-ranging wild felids the feline immunodeficiency virus is benign."

Van Vuuren said the disease was first discovered in a domestic cat in California in 1986, which led to a search for the virus in lions and other wild felids. Observation and testing of free-ranging lions, such as those in the Kruger Park, has led to the belief that the virus does not cause any problems in wild lions. "Wild felids have been living in harmony with this virus for probably hundreds of years."

It is only in domestic cats that the virus produces a progression of symptoms over several years, and causes immuno-suppression and leads to the eventual death of the animal. Prof van Vuuren added, "One cannot discount the possibility that a wild felid in captivity may, as a result of the unnatural conditions in which they are kept, develop a disease which would otherwise not affect healthy free-ranging animals."

The disease appears to be spread in large cats mainly through bite and scratch wounds.

Prof van Vuuren also stated that there is currently no evidence to support the theory that FIV and bovine TB in lions have the same relationship as TB and HIV/Aids in humans, where it is well documented that HIV in humans is often linked with tuberculosis. FIV does not appear to cause serious complications for animals with TB.

According to Prof van Vuuren, FIV has been detected in lions from South Africa, Namibia, Botswana, Zimbabwe, Kenya and Uganda. Like HIV, the virus appears to have evolved in Africa, along with lions, so that existing populations are more resistant to the virus. A similar resistance to Simian immunodeficiency virus (SIV), another related disease, appears to be present in African primates such as chimpanzees.

Bovine TB

Most recent testing of a sample of the lions from the southern parts of the park showed that approximately 80 per cent of the lions tested had been exposed to or were infected with bovine tuberculosis. However, only some of these show clinical symptoms at any one time. The highest concentrations of TB positive buffalo also occur in the south of the park. 

In the north of the park, most lions still test negative for TB at present. According to Bengis, the first known cases of TB in lions in the KNP were found when two emaciated lionesses were post mortemed in 1995. Lions are thought to contract TB from infected prey species, especially buffalo, being exposed to the bacterium that causes the disease when they eat infected animals. As lions frequently select an animal that looks easy to catch for their meals, a buffalo weakened by TB is a likely target. They also scavenge on carcasses of animals that have died of TB. The first cat into the kill, usually a dominant male, will eat the choicest parts, such as the lungs, which are a main site for the TB lesions and bacteria.

Buffalo and lions catch the disease in different ways, and the disease may progress differently in the two species. Buffalo, who are generally infected by droplets spread by coughing, tend to develop a chronic form of the disease, with a relatively slow progression of symptoms and overall loss of condition. 

Research into the effect of the disease in buffalo has led scientists to believe that they are a 'maintenance host' for bovine TB, as the disease has spread through most of the herds without significant effects on the population as a whole yet. Other animal species that are then infected via indirect or direct contact with the buffalo can be termed 'spill-over' hosts. Some of these hosts also have the potential to become a maintenance host, for example warthogs and kudu.

Lions usually develop more progressive symptoms than buffalo, with a shorter time span between infection and the first visible clinical signs of the disease, and the eventual death of the animal. In buffalo, the disease tends to concentrate in the lungs and the lymph nodes near the head. In lions, according to Dr Bengis, there is some evidence to suggest that TB may interfere with the digestive process, as well absorption of nutrients into the bloodstream, as lions with TB can become emaciated. He says that many of the TB positive lions that showed advanced clinical signs of infection also have TB lesions in their bones and joints that compromised their mobility. Lesions are also frequently found in the lungs of lions, possibly as a result of biting through the upper airways during strangulation or smothering of their prey.

One of the biggest problems facing research into the effects of TB in wild animals is that it is very insidious - once infected, an animal may take a long time to show symptoms, and those symptoms may have little visible effect on the animal's health for a relatively large proportion of the animal's lifespan before leading to its death. It is also relatively difficult to diagnose in the live animal. This makes any impact the disease may have on a population, as opposed to individual animals, difficult to establish.

Research in TB in lions

With the high numbers of lions that have been diagnosed as TB positive, a research project was started in 1999, where 16 TB positive lions in the south of the park and 16 TB negative lions in the north were identified and clinically evaluated. Vets have been monitoring the animals to see what the effects of TB are in lions. This study is also looking into any potential link between FIV and TB. The study is not yet concluded, and the final findings have not been analysed.

The study has looked at many things, including the life span of the study lions, any changes in the prides to which they belong, the birth and deaths of cubs in the study prides, and individual animal's blood profiles and weight.

Some problems were experienced with the study when the radio collars used did not live up to expectations, but after four years preliminary findings published in a project report show that of the 16 southern lions, 12 have died. Five died of TB and seven died either through being attacked by other lions or shot when they left the park, possibly as a result of the apparent disruption of the pride structure when the other individuals died of advanced TB. In the north, eight of the original study lions are still alive. 

According to Dr Gus Mills, a SANParks research fellow focusing on large carnivores, most prides in the Kruger Park are protected by a coalition of two males, usually brothers or half brothers. According to the report, the northern male lion coalitions remain in charge of their pride for longer than their southern counterparts. However, pride tenure by coalitions of males does vary across African ecosystems.

Kruger Park management is waiting for the study to be completed later this year, and say that until all the findings are analysed, no conclusions can be drawn as to what steps can or should be taken against TB. They added that they are looking at the matter in an objective way.

Dr Mills commented that although there are concerns about the level of infection, TB has been found in several wildlife populations around the world, and there are no examples where TB has had a major impact on the population. He added that it is part of the park's mandate to try to eradicate, or control exotic organisms, which it is believed TB is, but that both ecological and economic aspects must be looked at before any steps are taken.

Dr Bengis' concerns about TB stem from the fact that the prevalence and the spatial spread of the disease in buffalo and lions has been increasing progressively since it was first detected, and that it is being found in an increasing number of species in the KNP. He also said that in lions, which are top of the food chain, multiple exposures are likely, and the disease seems to have the highest prevalence in adult males. He said that the disease is a potential wild card, and that one should not "put one's head in the sand" and be complacent about this potential animal health problem.

He added that a vaccine trial is underway to evaluate a vaccine that prevents TB in buffalo, and that this may possibly be investigated for future use in lions. Vaccination programmes in free-ranging animals can be difficult to implement, and considerable research is generally necessary before such a programme can be launched.

Other researchers think that it is possible that buffalo and possibly lion may, in time, adapt to bovine TB without human intervention. This would occur through the natural selection of animals that are least susceptible to the disease. It is possible that the removal of sick animals from the population by predation may speed up the process, but it would still require several generations for the population to adapt.

To date, TB has been found in lion, buffalo, leopard, cheetah, hyaena, kudu, honey badger, warthog, genets and impala in the KNP.

 

November 2004