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The South African way of dealing with ASF

The Russian Federation continues to report outbreaks of African Swine Fever – but it is not the only country where the disease is tormenting the swine industry. South Africa has long had an ASF control area, but faced an outbreak outside the zone in 2011. A quick and coordinated response prevented further spread.

South Africa has an African Swine Fever (ASF) control area in the north-eastern part of the country (see Figure 1), where the virus is maintained in a cycle between warthogs and soft (argasid) ticks that live in their burrows. Domestic pigs become infected when the ticks feed on their blood. Control measures to prevent spread to domestic pigs include double fencing around piggeries situated within the ASF control area and a system of pig farm approval/ accreditation. Pigs can only be moved in and out of the area by veterinary permit to prevent spread to the free area and to reassure international trading partners that ASF is well controlled and they will not become exposed via infected meat or live animal importations. While sporadic outbreaks are recorded in the control area owing to failure to observe the control measures, the first outbreak outside the control area in more than 50 years occurred in late 2011.

In September/October 2011, pigs started dying at a small piggery within the ASF control area. The current indications are that the farmer sold some pigs at an auction at Sundra, outside the ASF control area in Mpumalanga Province. In the last months of 2011, farmers bought pigs at the auction that were sick and did not respond to antibiotic treatment. One farmer suffered severe losses, so sold 52 pigs (the surviving balance of his herd) to an abattoir in Gauteng Province on 3 January. After 28 had been slaughtered the meat inspector noted that several of the carcasses appeared septicaemic and stopped the slaughter line. Officials of the Gauteng Provincial Veterinary Services and a rural private vet were called in and made a presumptive diagnosis of ASF. Samples were sent to the Onderstepoort Veterinary Institute where the diagnosis was confirmed. As the abattoir and farm are on the Mpuma-langa and Gauteng boundary, state veterinarians from both provinces instituted back-tracing from the farm and identified the three auction yards at Sundra as the common denominator. All known buyers and sellers identified by back-and forward tracing were followed up (86 and 48 farms in Mpumalanga and Gauteng respectively plus one each in Limpopo and North West Provinces).

Quarantined
By 30 January, out of the 136 potentially infected farms, eight in Mpumalanga and four in Gauteng had proven positive or highly suspicious and were quarantined. Further farms were quarantined as the investigation progressed (see Table 1) but most were found not to be infected. One farm where positive pigs were identified did not have a connection to the auctions in Sundra and one positive farm bought pigs at a fourth auction site 150 km from Sundra. There was a ban on pig auctions at saleyards throughout Gauteng and within a 300-km radius of Sundra in Mpumalanga and monitoring was enforced, but it was observed that pigs arrived and were sold directly from vehicles in the vicinity without passing through the saleyards. There were about 500 pigs in quarantine on infected farms.

South Africa has a stamping out policy with respect to ASF, but since the outbreak was confined to a specific area and the number of pigs was low, the South African Pig Producers Organisation (Sappo) offered goodwill payments to expedite the slaughter.

Once the owners of the quarantined pigs had signed an agreement accepting a flat payment from Sappo, the National Society for Prevention of Cruelty to Animals was informed and requested to be present at all sites to ensure the act of slaughter was done humanely. The pigs were removed to a safe disposal site in the area and destroyed. This process occurred mainly in February although there were a few farmers who resisted the disposal of their remaining pigs. The longer the farmers delayed the greater their losses were. After disposal the facilities were disinfected and remained empty for 60 days before restocking was allowed.

New ASF situation
This outbreak represented a new ASF situation for South Africa. In the control area, outbreaks usually involve a single site where separation between pigs and warthogs is inadequate and the affected herd is stamped out. In this case, the main source of infection was commercial pigs although the outbreak is believed to have originated in the control area. Several factors contributed to its rapid containment. These include the meat inspector's action of stopping the slaughter line and contacting provincial veterinary officials and a private vet who made the right tentative diagnosis, took the right samples and sent them to the OIE reference lab, which confirmed the diagnosis within 24 hours.

This enabled the Provincial and National Veterinary services to quickly institute surveillance and forward- and backward tracing and to quarantine suspicious herds, which limited spread and enabled the probable primary source to be identified. The outbreak did not affect the mainstream commercial pig industry as it occurred in a different sector that has little or no contact with it. The rapid response and the fact that most of the large commercial farms are compartmentalised or practice a reasonable level of biosecurity contributed to keeping the industry safe. Pork exports to neighbouring countries were briefly interrupted as trading partners accepted the safety of pork emanating from compartmentalised farms.
Lessons to be learnt include: Be aware of the unexpected, and contact a veterinarian in the pig field if one is unsure. The system does work but flaws include lax control and education at saleyards and contravention of the law by farmers in the control area. The state vets must be more vigilant, know who who keep pigs and ensure that they have them correctly housed and bio-secure.

The pig industry owes thanks to the observant people concerned and itself deserves praise for being willing to pay incentives to farmers for slaughter of the pigs at confirmed sites. Stamping out of confirmed infected herds reduces possible spread and minimises the duration of crisis. The industry is planning a national serological survey in late 2012, to confirm that domestic pigs are free of ASF in and outside the control area so that trade agreements that include live pigs can be fully resumed.

Source: Pig Progress magazine 28.9 (2012)

Photo

  • Mary-Louise Penrith, Department of Veterinary Tropical Diseases, Faculty of
Veterinary Science, University of Pretoria, South Africa.

    Mary-Louise Penrith, Department of Veterinary Tropical Diseases, Faculty of Veterinary Science, University of Pretoria, South Africa.

  • A post mortem performed on a pig that died of ASF in early 2012. Photo courtesy of Dr Peter
Evans.

    A post mortem performed on a pig that died of ASF in early 2012. Photo courtesy of Dr Peter Evans.

  • In the control zone in Limpopo state, the ASF virus is endemic in warthogs.

    In the control zone in Limpopo state, the ASF virus is endemic in warthogs.

  • Tom Spencer, Department of Production Animal Studies, Faculty of Veterinary Science, University of Pretoria, South Africa.

    Tom Spencer, Department of Production Animal Studies, Faculty of Veterinary Science, University of Pretoria, South Africa.

  • The South African way of dealing with ASF

By Tom Spencer and Mary-Louise Penrith, Faculty of Veterinary Science, University of Pretoria, South Africa

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