Central SA
African swine fever viruses
13:51 (GMT+2), Tue , 19 March 2013
Central SA
Tampans in northern Gauteng infected with the African swine fever viruses

Dr Livio Heath
Transboundary Animal Disease Programme, Onderstepoort Veterinary Institute, Agricultural Research Council

In recent years South Africa has experienced a drastic expansion of game farming and related ecotourism activities. This has meant that several species of game have been reintroduced into areas that have previously been used for commercial farming. The increased likelihood that contact between wild life and domesticated animals may occur in these regions represents a significant threat of disease transmission to native domestic livestock.

Of particular interest to pig producers in South Africa is the threat that African swine fever (ASF) may be introduced into areas that have previously been free of the disease. ASF is currently restricted to the far-northern parts of South Africa where it is maintained in three epidemiological cycles. The sylvatic cycle involves wild suids and soft ticks. As the natural arthropod host of ASFV, tampans represent the link between wild suids and domestic pigs. In areas where domestic pigs are kept within the home range of wild suids, such as warthogs, the spread of ASFV to pigs is often facilitated by soft ticks.

Currently ASF is restricted to the northern parts of the country. However, anecdotal evidence has suggested that the distribution of warthogs and tampans associated with the species is slowly expanding southwards. Concerns have been raised that this expansion may have resulted in the dissemination of ASF beyond the current ASF control zone. In response, the Agricultural Research Council together with the Department of Agriculture, Forestry and Fisheries have been conducted surveillance in selected areas bordering the ASF control zone to determine whether the disease and its associated vectors have spread southwards beyond the current control zone.

During the first phase the project ticks were collected from various locations in Gauteng close to the ASF control zone. The ticks were transported to the ARC Onderstepoort Veterinary Institute where they were identified and tested to determine whether they were infected with the ASF virus. The primary diagnostic method used is based on the detection of DNA and was shown to be both highly sensitive and accurate.

However, one of the major drawbacks of using polymerase chair reaction (PCR) tests to detect pathogens is that the test does not generally discriminate between live and dead pathogens. To compensate for this shortcoming all ticks that tested positive using the PCR test were also subjected to classical methodologies, including virus isolation.

Of the total number of consignments subjected to testing, 3.5% tested positive for ASF genetic material by PCR. Interestingly, infectious virus could only be recovered from one consignment. These ticks were collected from the Mangena Nature Reserve situated approximately 50km north of Pretoria and are a considerable distance south of the ASF control zone. Genetic analysis confirmed that the virus is similar to other ASF viruses found in South Africa.

The results of this preliminary study tend to suggest that the distribution of soft ticks extends further south than previously reported. More importantly, the detection of the ASF virus in these ticks may represent a significant threat of disease to pig farmers beyond the current ASF control zone. However, more research is necessary to establish the level of risk along the entire ASF control line.
The ARC has embarked on a detailed study into the role of climate change not only on the distribution of ticks, but also on distribution of other insects that carry diseases such as Rift Valley Fever and African Horse Sickness. The risks posed by changes in the distribution of wildlife species, such as warthogs, due to increased wildlife farming are also being assessed. This will ensure that the livestock industry of South Africa is able to respond effectively to the challenges posed to these diseases.

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