Abstract Introduction
The second non-lethal bovine tuberculosis (BTB) detection survey was conducted on all significant (>150 animals) buffalo herds (Syncercus caffer) north of the Olifants River in the Kruger National Park from 4–27 July 2003. A total of 651 buffalo from 30 herds were sampled. The previous survey was conducted in various months in 2000 and coincided with the capture of pregnant cows and a few breeding bulls for the Koos Bekker and Skukuza disease-free breeding projects. No animals were captured for breeding purposes during the 2003 survey.1
BTB was detected in all herds tested south of the Letaba/Shingwedzi watershed and confirmed in one herd north of this watershed. Eight herds north of the watershed had suspicious results on either the gamma-interferon assay or tissue samples and we await the mycobacterial culture results to confirm the TB status of these herds. Confirmed BTB negative herds (from consecutive negative results in previous surveys as well) only occur north of the line running east-west through Dzundzini hill in the far north of the Kruger National Park. These results indicate a marked increase in the spatial spread of TB in the northern herds when compared to the 2000 survey and supports the theory that BTB will eventually spread to all buffalo herds in contact with each other in the Kruger National Park.
Methodology
The 2003 sampling of buffalo herds started on 4 July in the Letaba area and moved progressively northward up to the most northern herds in the Limpopo valley. The Olifants/Letaba watershed was the southernmost geographic limit of the survey. One to two herds were sampled per day. Herds were found either by fix-wing aircraft the previous afternoon and sampled the next day by helicopter or found directly by helicopter and sampled. A split subgroup was separated from the main herd and randomly selected animals were then darted from the helicopter using aluminum darts. Etorphine (M99) with azaperone and hyalase were used in the initial stages of the survey and M99 combined with A30-80 and azaperone was used in the latter part of the survey.
The sample size of animals selected per day depended on the estimated size of the herd: between 16 and 30 animals were captured per herd (10–16 at a time; therefore, more than one group were immobilized per day or on different days from larger herds). Blood samples were collected from each animal for the gamma-interferon tuberculosis assay, foot and mouth disease serology, and for corridor disease research.2 Serum samples and random DNA samples were collected for banking purposes and future reference. Probang samples were collected from most buffalo for F&MD virus isolation.
A radio collar was fitted to an adult cow in each herd tested, so that the group could be located 36 hours later. Each animal was identified on the back, with a painted letter of the alphabet allocated to that herd, and a specific number correlating to its blood samples for immediate future recognition. These identifying marks persisted for up to five days after which the paint was either rubbed off or obscured by dirt and mud. In addition to the paint, they also received a general ‘X’ hot brand ensuring the animals can be identified in future years as animals tested in 2003. After all the procedures were completed, a specific antidote was administered to the immobilized animals, thereby reversing the anesthetic agent. Most immobilized groups were found close together after being revived and no indications of post-capture predator related mortalities (or any other form of mortality) were recorded.
The gamma-interferon assay preparation was done immediately on return from the capture. Stimulated plasmas were incubated overnight, and results were available within 36 hours. If an animal tested positive or suspicious for TB then an attempt was made to get at least one positive animal from a herd, euthanatize it, and perform a detailed necropsy. Head and thoracic lymph nodes were excised and carefully examined for macroscopic tuberculous lesions. Lungs were carefully palpated, and the thoracic lymph nodes were excised and examined.
Discussion
Macroscopic lesions were found in all but one animal with a strong positive gamma interferon test, confirming the disease in that herd. That single macro-negative animal was, however, positive on culture. The gamma interferon test in free-ranging Kruger buffalo appears to have excellent sensitivity and specificity.2
The 2003 survey results indicate that there has been a significant increase in the number of positive herds in this region of the KNP, compared with the 2000 survey. All herds south of the Shingwedzi/Letaba watershed tested positive in 2003, whereas only four out of 12 herds were positive in this area in 2000. Disease detection in buffalo herds north of the watershed was much lower than herds south of this watershed, with only one animal having a confirmed positive result on BTB. This animal that tested positive was captured at Malahlapanga, approximately 20 km south of Punda Maria—this is the most northern point where BTB has been detected in the Kruger National Park to date. This animal tested positive on the gamma interferon assay and had a macroscopic lesion confirmed at necropsy. There were a number of herds north of the watershed with suspect reactions and we await the culture results from samples of euthanatized animals. With only one positive result but several suspicious reactions, as well as several previous confirmed cases at Nkokodzi, Tussen In, and Biesiesvlei (lion), it is suggested that BTB is present at a very low prevalence in the greater part of the far north districts.
We can accept for management purposes that all herds south of the line running east-west through Dzundzini hill are infected at a very low prevalence with BTB. Herds south of the Shingwedzi/Letaba watershed are infected at low to medium prevalence. As of 2003, herds north of the east-west line through the Dzundzini hill are still considered negative for BTB since multiple buffalo capture and sampling opportunities over the past four years have failed to detect any TB in this area.
The next non-lethal BTB survey planned for 2005 will only be conducted north of the Shingwedzi/Letaba watershed as we have now shown that all herds south of this line are infected. There is still merit in doing the non-lethal sampling in the low-incidence herds in the north of the park to avoid killing healthy buffalo in this way. Should there be a need to determine more precise prevalence of TB in the infected herds between the Letaba and Shingwedzi Rivers, a lethal sample is recommended, as this will be more cost effective.
The continued monitoring of the TB status in the KNP buffalo herds cannot be over-emphasized, as the knowledge gained is unparallel elsewhere in wild populations. We have a commitment to our neighbors (both livestock and wildlife interface) to inform them of the risks and only with up-to-date information of the disease and its status in the Park, can rational management decisions regarding possible containment, control, and eradication measures be made.
Acknowledgments
This survey would not have been possible without the excellent support of the district rangers, section rangers, and field rangers of the northern regions of the park. The technical staff from the regions also provided support without which we could not have managed. Special thanks must go to Louis Olivier for his clinically perfect organization of staff, observers, and general logistic support!
Anita Michel from the OVI and Cornelia Gerstenberg from the National Directorate of Animal Health supported our work from their Institutes/Departments, for which we are very grateful. The State Veterinary Team (Dewald, At, Schalk, Kenneth, and Johan) was an integral part of the exercise and is thanked for efficient professional assistance. Eunice, Jenny, the students (Monika and Dean), and our own staff (Marius, Hoepel, David, Ernest, Sollie, and Amos) were highly efficient and we could not have done it without their loyal support and effort.
Judith Kruger and Sandra MacFadyen provided prompt GIS back up and provided the maps attached to this document. Many thanks to them as well.
We would all like to thank the three pilots involved (Martin, Hennie, and Fanie) who made the actual sampling possible in their typically professional way. All in all, it was a great team effort, and foreign colleagues visiting the operation remarked positively on the planning, efficiency, and co-operation that existed between all role players.
Literature Cited
1. Grobler D. KNP Bovine Tuberculosis Survey 2000. Internal Scientific Report. Skukuza, RSA: South African National Parks.
2. Grobler D, Michel AL, De Klerk LM, Bengis RG. The gamma-interferon test: its usefulness in a bovine tuberculosis survey in African buffaloes (Syncercus caffer) in the Kruger National Park. Onderstepoort Jnl Vet Res. 2002;69:221–227.