PDF《African buffalo (Syncerus caffery》

120 over into warthog (Phacochoerus aethiopicus) popu- lations. In the Kruger National Park (KNP), mycobacteriosis in wild animals was first described in November

1967 in an impala (Aepyceros me/ampus) from the Croco- dile Bridge area south of the Sabie River (De Vos, McCully &

Van Niekerk 1977). No isolation of the causative organism was attempted and, on histo- pathological grounds alone, a diagnosis of the avian form was made. The disease entity caused by Mycobacterium bovis, and known as bovine tuberculosis (abbreviated as BTB), was first detected in the KNP in July

1990 (Bengis, Kriek, Keet, Raath, De Vos &

Huchzermeyer 1995). The disease was diagnosed on necropsy of a two-year-old buffalo bull, which had been found in an emaciated and moribund state near the south- western boundary fence. This prompted an investi- gation into the BTB status of the rest of the buffalo population, and its significance as a disease entity in the KNP. This report documents the findings of the surveys that were conducted from 1990-1996. MATERIALS AND METHODS Study area The KNP is an elongated nature reserve which is situated along the north-eastern border of South Africa. It comprises about two million ha of gently undulating hills and doleritic dykes, grassy plains, parkland savannah, dry deciduous forest and thorn- bush, and is inhabited by

132 free-ranging mammal species of which

20 can be classified as large mam- mals (Pienaar, Joubert, Hall-Martin, De Graaff &

Rautenbach 1987). A buffalo population of

29500 was documented during the

1991 aerial census. The eastern, southern and western boundaries of the KNP are fenced in by a game deterrent fence. Due to flooding, efforts to fence the extreme northern tip bordering on Zimbabwe, have been largely unsuc- cessful. In recent years most of the western fence between the Sabie and Olifants Rivers has been removed to allow free movement of wildlife between the KNP and the adjoining private nature reserves. For all practical purposes it shifts the western bound- ary south of the Olifants River about

20 km further west and adds a further

220000 ha to the Greater KNP complex, with an additional

2800 buffalo. The remaining southern and western areas bordering on the KNP are used mainly for agricultural purposes. Since the early 1970s the emphasis on livestock and irrigation farming to the west of the KNP has shifted gradually towards private game farming. In some of these areas livestock, especially cattle, are still found in the proximity of the boundary fence. On the Mo- zambique side subsistence agricultural practices predominate. Surveys During 1991/1992 use was made of the ongoing buf- falo population refuction (culling) operations for the post mortal surveillance of BTB. However, as a result of a natural die-off of buffalo in response to severe drought, culling operations on buffalo terminated in 1993. A total of

1974 buffaloes, culled in June to July and October to November of 1991, May to August of

1992 and November 1993, were utilized for the BTB survey. On average,

35 animals were killed per herd. Random sampling, as described by De Vos, Bengis &

Coetzee (1983), was practiced. For the evaluation of ante mortem BTB diagnostic tests, a further

86 buffalo in groups of 8-11, were examined in 1991,

1992 and

1993 from known positive BTB herds in the southern sector and known negative herds in the far northern sector of the KNP (The re- sults of these tests will be reported on elsewhere). Of these,

45 were selected for poor body condition, or lagging when chased by helicopter. When these tests were concluded the animals were slaughtered and necropsied. In 1996, in order to ascertain whether BTB had crossed the Olifants River, and to establish the disease'