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Top-rate biosecurity measures and the ongoing implementation thereof by large- and small-scale producers in the South African pig industry deserve renewed attention. Disease transmission is something that the herds of all producers, regardless of their level of production, are exposed to.
Dr Nadia de Beer, a veterinarian at Agri Farmacy SA in Potchefstroom, believes that even though some disease-causing pathogens are not visible to the naked eye, this does not mean they are not present. The dreaded African swine fever (ASF), she emphasises, is a disease that is occurring more frequently outside of the country’s controlled area. Preventing ASF and other animal disease outbreaks in intensive production systems, she believes, is more successful and cost-effective than attempts to treat it.
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This comes after several provinces in the country experienced an uptick in outbreaks this year. Outbreaks have also been reported in the Potchefstroom area in North West since February. The index case occurred on a smallholder farm, and high pig mortality rates were recorded. Subsequently, two more farms in the area, one a commercial unit, also reported outbreaks. The latest ASF outbreaks in this province occurred in May and June among free-range pigs in the Rustenburg area.
Dr Livio Heath from ARC-Onderstepoort Veterinary Research agrees that excellent biosecurity measures are the best defence against ASF, especially since there is no effective treatment and no vaccine for this virus.
Emphasis on ASF
African swine fever is a controlled animal disease in terms of the Animal Diseases Act, 1984 (Act 35 of 1984). This means the disease must be reported to a state veterinarian.
De Beer mentions data from the World Organisation for Animal Health (OIE) showing that Africa, Asia and Europe are worst affected by ASF. However, it remains a major concern for veterinary authorities and the private sector worldwide.
According to Heath, ASF is a highly contagious viral disease – affecting pigs of all ages and origins – which has a deadly effect on infected units. It is not a zoonosis and cannot be transmitted from animals to humans. It affects only pigs, including wild pigs and warthogs. Live pigs or carcasses spread the virus, while pork products derived from domestic or wild pigs can also spread the disease.
ASF is highly resistant to environmental conditions and can spread through contaminated animal feed and fomites (non-living objects) such as shoes, clothing, vehicles, knives and equipment.
Clinical signs of ASF
De Beer lists some clinical signs of ASF, including high fever, weak pigs that have difficulty standing up, decreased feed intake, coughing and other respiratory signs, as well as digestive abnormalities such as vomiting and diarrhoea. Other characteristic signs are a red or purple discoloration of the skin around the ears, stomach and limbs, as well as bleeding from the nose/rectum. Sows can also abort.
ASF’s main feature, she says, is its high mortality rates. The incubation period is four to 19 days, meaning most infected animals will die within four to 19 days.
Distribution and control of ASF
According to the Department of Agriculture, Land Reform and Rural Development’s Directorate Animal Health’s report on ASF outbreaks dated 23 July 2021, the first outbreak was reported in February this year in the Western Cape. The report shows that Gauteng has seen numerous outbreaks since October 2020, with the original cases implicating the auctioning of pigs as a likely source of infection.
The report states that the ARC-Onderstepoort Veterinary Research’s cross-border laboratory for animal diseases in Gauteng isolated two genotypes of the virus. Genotype 1 was isolated in outbreaks in North West, Mpumalanga, Gauteng, Free State and the Northern Cape, while Genotype 2 was isolated in outbreaks in North West, Gauteng, and the Eastern and Western Cape.
De Beer says control measures are based on quarantine and movement control. Continued awareness campaigns, emphasising essential biosecurity measures, have been put in place. Although difficult to control, adds Heath, basic biosecurity measures are very successful in preventing the disease from being introduced into healthy pig populations.
Protect your herd through the following biosecurity measures:
- Avoid buying animals from unsafe sources.
- Apply access control for visitors and staff. Only the owner, relevant employees and health officers should be allowed in a unit.
- Vehicle access control is crucial. According to Heath, trucks transporting animals and food scraps must be cleaned before and after, and disinfected using registered agents. Trucks must not park near pens, and truck drivers should not leave their vehicles.
- Safe feed is vital and food waste that may contain uncooked or contaminated pork and products should not be fed to animals, warns Heath.
- Use registered disinfectants and apply pest control.
De Beer adds that pig owners should use fences to control free-range pigs.
Research and observation
As soon as ASF is suspected in a herd, a state veterinarian or animal health technician will investigate and take a sample. Based on the history and clinical signs and/or post-mortem findings, the property is then placed under quarantine, pending the outcome of an investigation.
A quarantine notice is given, including a ban on all movement on the property. Owners of surrounding properties are also informed of the outbreak.
According to Heath, most experimental vaccines, which use a modified form of ASF, were unable to protect pigs from infection. One of the reasons is that the virus targets the immune system and prevents the animal from developing immunity.
Despite these challenges, though, several experimental vaccines are currently being evaluated in Asia. “Unfortunately, it is unlikely that these vaccines will be of much use in Southern Africa, as different variants of the virus are found here.” Heath says multiple vaccines are needed to combat all the variants.
The Agricultural Research Council (ARC) houses the OIE reference centre for ASF at its Onderstepoort campus and this centre has been central in the diagnosis and control of ASF since the 1980s. Current research activities focus mainly on identifying disease variants occurring in Southern Africa, as well as the development of control measures that apply to large commercial units and local small-scale pig producers.
The ARC, in collaboration with the University of Pretoria, also investigated the spread of ASF among game in South Africa so as to determine its long-term risk to the local pig industry. “We are also involved in efforts to develop safe and effective vaccines for the disease as part of international efforts to control it,” says Heath.
For more information, contact Dr Nadia de Beer on 018 297 8155 or firstname.lastname@example.org, or send an email to Dr Livio Heath at HeathL@arc.agric.za.