By Dr Lin-Mari de Klerk-LoristDuring the last two weeks of July the Veterinary Wildlife Services Unit of Kruger National Park launched an operation to determine the true prevalence of bovine tuberculosis (BTB) in the buffalo population of the Shingwedzi river catchment. From previously collected data during the buffalo and elephant census, twelve fixed point locations were randomly selected as capture areas.
Survey Determines Bovine TB Prevalence in Shingwedzi Area
Every morning the ground crew departed about an hour earlier than the aircrew, heading out to the suggested capture area. The aircrew scanned the area for any indication of buffalo activity and buffalo herds nearest to the fixed point locations were then selected for sampling. Depending on the size of the herd, a number of buffaloes were sampled, representing the general structure of a herd. For instance, if the aircrew estimated that there were 200 buffalo in a herd, the sample contained two adult bulls, four adult cows, four sub-adults and four juveniles. All the buffaloes were darted from the helicopter by a veterinarian.
The ground crew were called in after all the animals were immobilised. The team had to work very fast to get all the samples and data collected as soon as possible, to prevent unnecessary stress on the animals. The blood samples that were collected from each individual had to reach the laboratory within six hours after collection. Every buffalo received a large unique number in silver paint on its back, so that it could be easily identified from the air. One animal from the group was fitted with a radio collar so that their movements could be tracked the following day. A whole blood test was used to diagnose BTB in the buffaloes. The results of these tests were generally available within 26 hours after the animals were captured. From the 229 buffaloes that were captured during this period, 10 buffaloes had positive test results for BTB and eight showed mixed reactions.
The 10 test positive animals were relocated and euthanased to allow proper post mortems to be performed. Six of the 10 test positive animals had lesions visible to he naked eye, typically associated with animals infected with M. bovis. Two animals showed some lymph node abnormalities that could be linked to early infection while another two had no visible lesions.Tissue samples were collected during the post mortems and culture as well as histopathology results are pending. Final results should be available within the next three months. It is generally accepted that all the buffalo herds in the Shingwedzi river catchment are infected with bovine tuberculosis, but at a very low prevalence though.
After the statistical calculations were applied to the sample size, the sensitivity and specificity of the diagnostic test, it was estimated that the prevalence of this disease in the buffalo population of this area is somewhere between two and eight percent.
Although the prevalence in buffaloes is still low at this stage, the spill-over into the lion population has already occurred. With an increase in disease prevalence in future, as has been experienced in other areas of the KNP, spill-over into several other species remains a risk.