A new strain of TB may signal potential disaster for 10 000 buffalo in the Kruger National Park, writes Ellen Bartlett
SOUTH AFRICA, already facing the worst human tuberculosis epidemic in the world, is now confronting a new TB threat. Mycobacterium bovis, the strain commonly known as bovine TB, is sweeping the buffalo population in the Kruger National Park.
Nearly half the buffalo herds in the two million hectare park are considered infected. The epidemic is concentrated in the southern half of the park with nearly every herd south of the Olifants River affected, some with an infection rate as high as 85%.
The disease also has jumped to other species, including lion, cheetah, kudu and even a troop of baboons living near park headquarters at Skukuza.
A study group has been formed to come up with a strategy for containing the disease – and to reduce the potential for spillover to valuable export species such as white rhinoceros.
One proposal initially considered but then dropped would have required the slaughter of as many as 10 000 infected buffalo in the southern half of the park.
The plan was to create a buffalo-free zone starting at the Olifants River. Every buffalo found within the 20km wide zone would be shot. The zone would gradually be moved southward, eradicating the diseased buffalo from the southern half of the park, and allowing for repopulation by TB-free buffalo from the north.
The park has put the plan on hold, however, saying it needs to do more research. Recent surveys have also found that the infection has moved north of the Olifants River, which would have rendered the plan inoperable anyway.
“We still do not know enough about the disease. At this stage we are going to try, by good fencing, to contain the disease within the Kruger National Park complex, and do much more intensive research,” said Dr Devald Keet, senior state veterinarian in the park.
Of particular concern is the potential for the disease to spread out of the park and into the rural communities on its western boundary. Buffalo could easily infect domestic cattle living on the other side of the fence. The disease could then infect the human population via unpasteurised milk. It is symptomatically indistinguishable from the TB bacterium that commonly infects humans.
In fact, mycobacterium bovis can cause disease in a wide range of domestic and wild animals.
Scientists suspect that TB has been present in the park since the early 1960s, when a farm at Crocodile Bridge, in the southwest corner, near Komatipoort, had such a severe outbreak its entire domestic cattle herd had to be slaughtered. Back then the park was unfenced, and the infection could have been passed easily into the wild buffalo populations.
The only reason TB was never detected, scientists suspect now, is because no one ever felt the need to look for it.
Then in 1990, a young buffalo bull was found wandering and ill in the west of the park. He was shot and the autopsy showed he had TB. A subsequent survey of the buffalo population, involving testing buffalo shot in the annual cull, showed an astoundingly high infection rate.
In September 1995 a dead lion was found, autopsied and found to be severely infected with TB. The following March the infection was identified in kudu. The total number of other species infected is small but still worrying- three lions, six kudu, two cheetah, and the baboon troop.
Keet encountered the first infected baboon at the petrol pumps at Skukuza, too depressed and ill to run. The baboon was one of a large troop known as the Train Bridge Troop.
Keet and others suspect the omnivorous baboons contracted the disease by scavenging infected animals.
Tests on infected kudu show they are carrying a slightly different strain of the bacteria, indicating that it has come from a different source to the bacteria infecting the buffalo.
Though TB is rife among the buffalo, its spread to other species does appear to be limited to a few individuals. Because of that, and because the vast majority of diseased buffalo seem perfectly healthy, the park has opted for the more conservative approach, including close monitoring of the buffalo, following the progress of infected individuals and herds over a period of years, and closer study of mycobacterium bovis itself.
Park veterinarians are also looking for better means to diagnose TB in wild animals. At the moment only bovids and primates can be successfully tested without resorting to autopsy.
It is possible, scientists say, that the TB epidemic could continue for many years without having an undue effect on the populations.