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Biosecurity Key to ASF Control in South Africa

30 June 2016

SOUTH AFRICA - African Swine Fever in pigs has been likened to the Ebola-virus in humans. Dr Mary-Louise Penrith and Simon Streicher talked to Glenneis Kriel after the latest outbreak in South Africa.

South African pork exports recently came to a halt due to outbreaks of African Swine Fever in the North West and Free State provinces. Simon Streicher, CEO of the South African Pork Producers Association, said the outbreak didn’t have a big impact on commercial production, as it only affected small-scale producers.

“Most commercial producers have sound biosecurity measures to prevent an outbreak. Small scale producers, on the other hand, cannot always afford these measurements, which ironically are aimed at protecting their investments,” Streicher said.

While South African pork exports to Namibia have been halted, trade is anticipated to resume soon, because South Africa has a compartmentalisation agreement with Namibia. Farms conforming to the agreement have very strict biosecurity controls, according to Streicher, such as double fencing, with fences extending 0.5 meters below the surface.

The fences are also five meters apart to prevent truck access. There is no access to pig areas by vehicles except the farm’s own vehicles and the production area is regularly monitored by veterinarian authorities to enable certification.

Huge problem across the world

African Swine Fever is not just a problem in Africa. It is a serious disease that has been plaguing Eastern Europe and Russia since 2007, according to Dr Mary-Louise Penrith, an expert consultant to the Food and Agriculture Organisation of the United Nations on African Swine Fever.

“It is believed that African Swine Fever was introduced into the Republic of Georgia in 2007 through infected galley waste that became accessible to livestock. From there it spread to Armenia and Russia, and ultimately, by 2014, via Belarus to Poland, Latvia and Estonia in infected wild boars,” Dr Penrith explained.

She said the disease was in pigs what the Ebola virus was to humans. “African Swine Fever is caused by the Asfivirus. The disease, which doesn’t affect humans, manifests in acute, severe haemorrhagic fever in pigs. It usually cause a hundred per cent mortality and has wiped out whole herds of pigs on farms where outbreaks occur,” Dr Penrith said.

There is currently no vaccine or cure for the disease and eradication on the African continent is impossible, as the disease is endemic to African wild pigs, in particular warthogs. There have been a few non-African countries where the disease has been eradicated, but this came at a very high cost.

Brazil for example culled 66 902 pigs when an outbreak occurred around the mid-1980s. In Cuba, however more than 500 000 pigs were eradicated as well as the entire pig populations of Haiti and the Dominican republic.

Challenges

There are various reasons why the disease is so difficult to control. First, there is no vaccine. Even so, there seems to be a low percentage of pigs inherently resistant to the diseases.

“These pigs show no clinical signs, but develop antibodies if infected. Like African wild pigs they have low or no viraemia and are apparently not able to transmit infection for more than thirty days post infection,” Dr Penrith said.

Resistance seemed to increase in populations where African Swine Fever was endemic and Iberian breed pigs and their descendants appeared to have greater resistance than other breeds.

Secondly, pigs can shed the virus for up to forty-eight hours before developing clinical signs. As a result they could infect many other pigs before there are any signs of danger. According to Dr Penrith this has been the cause of an outbreak in South Africa on commercial farms back in 2011, when an infected pig caused the disease to spread to other pigs at an auction.

Thirdly, clinical signs, were not very specific. These included loss of appetite, lethargy and reluctance to move, huddling together and tremors, as well as flushing of extremities and ventral skin in white-skinned pigs. Variable signs included, abdominal pain, vomiting, constipation, diarrhoea and blood in faeces, ocular and nasal discharge, hind limb weakness and ataxia, difficulty breathing and sometimes bloody froth at nostrils, abortion at any stage of gestation and nervous signs in pigs that survive longer. Laboratory confirmation was therefore essential.

Pigs usually developed the disease through the ingestion or inhalation of infected material, such as meat from infected pigs, objects contaminated by secretions and excretions of infected pigs, mechanical transmission by bites of stable flies and injections with contaminated needles or bites from soft ticks.

No cure

In the absence of a cure, the disease has become a controlled disease in most countries. Producers therefore have to notify the State veterinarians of an outbreak to eradicate the disease and dispose safely of affected animals. The production area also needs to be disinfected and new pigs should only be introduced into the area forty days after disinfection.

Dr Penrith said that sound biosecurity measurements were the best way to prevent the disease. Farmers need to prevent contact with potentially infected pigs, African wild pigs and, where they occur, European wild boars. Free-range production is definitely a high risk and production should therefore be confined to pig-proof premises, such as pig sties or a fenced or walled camps.

New pigs and boars for services should only be bought from reputable sources and these animals should be isolated from the rest of the herd for at least fourteen days to ensure they are free from infectious diseases. “Two weeks is usually enough to identify whether pigs are infected by most of the infectious diseases,” Dr Penrith said.

Producers should prevent pigs from eating infected meat. The production area should be clean. Infected carcasses and material need to be removed to prevent scavenging and no swill should be given to pigs that contain pork products.

“Swill can be cooked for thirty minutes with constant stirring to destroy the virus if there is any uncertainty as to whether the swill contains pork products. The swill should be cooled down before it is fed to the pigs,” Dr Penrith said.

Access to the pigs should be limited. Veterinarians should put on clean clothing when they come onto your farms. Speculators should stay out of the production area. Producers and workers should stay away from farms where there are sick pigs and producers shouldn’t buy or accept leftover feed, feed bags or bedding from other pig producers. Footwear, hands and equipment also need to be decontaminated and disinfected before being allowed into the production area, according to Dr Penrith.

African Swine Fever can be transmitted by stable flies for up to forty-eight hours after sucking blood from an infected pig. Dr Penrith suggested that producers removed dung and compost from the area where the pigs are kept and use fly papers, traps and gauze over windows to manage fly problems.
Ornithodoros ticks are hosts of the virus.

According to Dr Penrith, some of these species live in crevices or soil in pig sties and feed on the blood of pigs. They can remain infected for at least five years. Producers should ensure there are no hiding places for these ticks in their pens. Since the disease can also be transmitted through contaminated needles, only one needle should be used per pig during vaccination or treatments. This is especially important if more than one herd is being injected. Needles can be sterilised by boiling them for fifteen to twenty minutes.

For more information contact Dr Mary-Louise Penrith at marylouise@vodamail.co.za

 

Top image via Shutterstock



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