Foot-and-mouth disease in a kudu (Tragelaphus strepsiceros) in Botswana.

IN Botswana, clinical foot-and-mouth disease (FMD) has been commonly reported in cattle but rarely in other species (Anon 2001). Outbreaks in goats and sheep are rare and reported to be mild (Falconer 1972). Buffalo (Syncerus caffer) are known to be the maintenance hosts of the FMD virus in the environment (Hedger 1976, Bengis and others 1986); they can be infected with FMD virus without exhibiting any clinical signs of the disease. Young buffalo calves between the ages of six and eight months may occasionally develop clinical FMD, possibly because maternal antibody protection begins to wane (Young and others 1972). Studies in Botswana and the surrounding region indicate that the majority of buffalo herds are infected with FMD Southern African Territories (SAT) viruses (Mapitse 1998). For these reasons, buffalo are confined to game reserves and national parks in the north west of the country. Their presence in livestock areas is considered a disease threat, such that they are immediately returned to the wildlife area or, where this is not practicable, they are destroyed and tested for FMD. Cattle in adjacent areas are vaccinated for FMD with a trivalent FMD SAT 1, 2 and 3 vaccine at least twice a year (Anon 2002). Other cloven-hoofed wild animals such as the greater kudu (Tragelaphus strepsiceros) and impala (Aepyceros melampus) are reported to be susceptible to experimental or natural infection with the FMD virus under favourable conditions (Walker 1934, Keet and others 1969, Hedger and others 1972). Natural transmission of FMD infection occurs, though not readily in kudu and impala, when there is an outbreak in cattle, or if carrier buffalo are present within the antelope homing range. Such infections are mainly subclinical, with only serological evidence of the presence of, or previous exposure to, the FMD virus. Only mild clinical disease has been reported in these species. In previous outbreaks of FMD in cattle in Botswana, other cloven-hoofed species did not get infected (Falconer 1972). Similarly, there was no evidence of disease or infection in these species in previous FMD surveys in Botswana. For these reasons the role of cloven-hoofed wildlife other than buffalo in the epidemiology of FMD in Botswana has been considered insignificant. This short communication reports the discovery of clinical FMD in a kudu during the 2003 outbreak of the disease in cattle in Botswana. Greater kudu are large antelopes found throughout southern Africa. They are timid animals that prefer to browse in thick bush habitat where they also benefit from camouflage; they tend to run for cover when approached. They are gregarious animals that live in small family groups comprising a bull and several cows and youngsters. Male kudu have big twisted horns, but the females have no horns at all. Botswana shares a long border with Zimbabwe, which is delineated by a seasonal river, the Ramokgwebana river, which is also a source of water for all animals in the area. On the Botswanan side of the river, there is a 1·4 m-high double cordon fence very close to the bank, which prevents the movement of domestic animals between the two countries. In Botswana, water is reticulated to inland watering points, up to 200 m away from the riverbank. On the Zimbabwean side, animals have direct access to the river. Wildlife could easily jump this fence and move freely between the two countries. Botswana experienced an outbreak of FMD in cattle in the Matopi extension area in the north eastern region. The outbreak was detected on January 5, 2003, in cattle at Matopi crush, a departmental cattle handling facility used for epidemiological surveys along the border with Zimbabwe, which is communal to one or more herds. This was the second FMD outbreak in two consecutive years in a previously FMD-free area (without vaccination). Four samples taken by probang, six samples of foot epithelia and nine of sera were submitted to the Institute for Animal Health (IAH) FMD Reference Laboratory in Pirbright, UK, via the Botswana Vaccine Institute (BVI), for FMD virus isolation and antibody detection. Virus isolation was carried out in primary bovine thyroid (BTY) cells and in a continuous pig kidney cell line, designated IB-RS-2. Both cell lines yielded negative results for all probang and foot epithelial samples after two passages. Serum samples were tested for SAT 1, SAT 2 and SAT 3 FMD antibodies by the liquid phase blocking ELISA method (Hamblin and others 1986a, b, 1987). Antibody titres were calculated by the method of Kaerber (1931) and were expressed in logarithms to base 10 (log10) Eight of the nine sera were strongly positive for antibody to FMD SAT 1, with only weak cross reactivity to the other SAT types. The antibody titres ranged from 724 to greater than 2048. It was subsequently concluded that the outbreak was caused by FMD SAT 1 virus. On January 12, 2003, a veterinary team on a routine surveillance operation in the Mokateng crush area found a female kudu, aged about three years, with lesions suggestive of FMD. The crush was less than 5 km from the Matopi crush and fell in the same extension area, which at the time was designated as the FMD control zone. The animal was lame and very thin. On visual inspection, foot lesions similar to those seen in cattle with FMD at the Matopi crush were noticed. The animal was euthanased and a thorough examination conducted. The kudu was emaciated and all four feet exhibited signs of severe coronitis and laminitis with advanced hoof separation. There was a healed interdigital ulcer on the left forefoot. The only oral lesion was an ulcer on the dorsal aspect of the tongue. The lesions were estimated to be more than two weeks old. There was extensive serous degeneration of visceral and omental adipose tissue, suggestive of severe starvation. Tissue and blood samples were collected. On the basis of the clinical picture, the disease in the kudu was considered to be FMD and appropriate precautionary measures were immediately implemented. After postmortem examination the carcase was burned and buried in a pit lined with 4 per cent sodium carbonate. The BVI referred the samples to the IAH in Pirbright, UK, for virus isolation and serological testing. Isolation of FMD virus and antibody detection was performed as described previously. No virus was isolated from either mouth or foot epithelial samples after two passages in both BTY and IB-RS-2 cells; however, the lesions in both the cattle and kudu were old, which might explain the failure to isolate the virus. The samples were further examined for FMD virus RNA using the reverse transcriptase-PCR, which also gave negative results. The sera were strongly positive for antibodies to FMD SAT 1 (titre 2048), with weak cross reactivity to the other SAT types, in keeping with the cattle samples tested previously. It was therefore concluded that the disease found in the kudu was FMD caused by SAT 1 virus. Following confirmation of the disease in the kudu, a team composed of veterinary and wildlife personnel was immediately mobilised to capture, inspect and sample as many wild cloven-hoofed animals as possible to establish Veterinary Record (2006) 159, 252-253