Ecology of wild and domestic suids in relation to the epidemiology of African swine fever in northern KwaZulu-Natal

Abstract

African swine fever (ASF) affect wild and domestic stock and can cause extensive socio-economic damage. The main objective of this study was to understand the role of Ndumo Game Reserve (NGR) and its surroundings in the ecology and epidemiology of the two diseases as well as the implications of pig husbandry practices in disease transmission. This study area was chosen because the game reserve shares its northern boundary with Mozambique where ASF is endemic. The study area, which lies within an ASF control zone, also shares its western boundary with eSwatini, which is ASF free. It is therefore to be expected that the NGR and surroundings is a high-risk area for the aforementioned diseases, making regular assessments pertinent. ii Line transect counts revealed a warthog density of 3-5 individuals/km2, with a total population of 400-500 warthogs in the study area. Most of the bushpig recorded on camera traps (0.515 animals/camera day) were found in habitats close to water. Warthogs (0.536 animals/camera day) on the other hand, were found in sandy environments. Fence survey results indicated that wild suids regularly cross the fence into the neighbouring farming community, particularly during the dry season. This was corroborated by 11 farmers who indicated that they had seen wild suids in the area. Questionnaire surveys, from the 254 domestic pig farmers, determined that most of the farmers free-ranged their animals outside of the cropping season. This finding, coupled with the observation that pigs periodically breach the game fence, is significant for disease management as it points to the potential existence of domestic-domestic and wild-domestic interactions which can facilitate disease introduction and spread. The risk of disease introduction is further heightened as some farmers purchase pigs outside the study area, particularly from Mozambique and eSwatini, and these movements are not reported. Social network analysis showed substantial movements (through buying and selling) between pig farmers connecting all villages in the study area. These movements can exacerbate the risk of disease introduction and spread. Even though the location of the study area suggests the potential presence of the diseases, burrow surveys (n=35) did not provide evidence of Ornithodoros tick infestation, implying that a sylvatic ASF cycle is currently unlikely to be present in the area, suggesting that ASF is unlikely to be present in NGR. Furthermore, blood samples of domestic pigs (n=67) tested negative for both ASF. This view is supported by the fact that the farmers reported no clinical signs or sudden deaths of pigs due to ASF in past years. Although no evidence of the presence of the two diseases was found in the study area, the area remains a high risk area for these diseases and ongoing disease surveillance is recommended. It is also recommended that farmers be educated on the best pig husbandry methods in order to reduce the risk of disease introduction and transmission.