The recent outbreak of African swine fever (ASF) in China represents a significant development in the progression of the disease. China is home to over half the world’s pig population (around 500 million pigs) so any potential spread throughout China and neighbouring countries would be devastating. With no vaccine to aid its prevention and control, researchers at The Pirbright Institute are joining forces with other research organisations and policy makers to help limit the damage caused by this deadly pig disease.

The silent killer...

Infection with ASF virus (ASFV), which causes the disease, can result in pig fatality rates of up to 100%. In addition to the lack of a vaccine, control of ASF is hindered by the many transmission routes through which the virus can spread. Wild boar act as a reservoir for the disease, enabling the virus to circulate unchecked and allowing its spread to domestic pig farms. Boar carcasses can remain infectious for long periods given the right conditions.

Outbreaks in Eastern Europe have moved as far as the Czech Republic, triggering authorities in Germany and Denmark to employ wild boar culling and border fence improvements in an attempt to prevent further spread into ASF-free countries. The populations of wild boar in China may prove a significant risk factor in maintaining ASF reservoirs, but little is currently known about their distribution and corridors of movement.

ASFV can also be transmitted by ticks that feed on infected wildlife in east Africa, and through consumption of infected meat by pigs. The virus is able to survive in frozen meat for months or even years, so stringent import regulations for pork products are an essential preventative measure. The Animal and Plant Health Agency (APHA) has reiterated that it is illegal to feed domestic food waste or catering waste of any description to farm animals in the UK. This includes all pigs, whether kept commercially, on small holdings or as pets. Read the APHA announcement on the government website.

Pig keepers can also help prevent infection by practicing good biosecurity. Routinely providing dedicated clothing and boots for workers and visitors, limiting visitors to a minimum, and preventing outside vehicles which may be contaminated from coming on to pig premises, are valuable procedures for keeping out African swine fever.

Last summer APHA and Defra upgraded the ASF threat to the UK from ‘very low’ to ‘low’ – meaning the risk is “rare but could occur” (European Food Safety Authority terminology). To raise awareness amongst veterinarians and farmers, Pirbright scientists have collaborated with APHA to produce a resource which details the clinical signs of pigs infected with ASF.

What the scientists say...

Dr Linda Dixon, African swine fever expert at Pirbright, said: “We hope that by creating resources such as these, we can increase the likelihood of vets and farmers identifying the disease quickly should an outbreak occur in the UK. Thorough surveillance and rapid diagnosis of ASF are essential for its control, services which Pirbright provides globally as the World Organisation for Animal Health (OIE) Reference Laboratory for ASF. Using our expertise, we can advise Defra and OIE as well as improving tests to detect the virus more accurately and rapidly.”

ASFV does not cause disease in humans but it poses a significant threat to food security and has a substantial impact on the economy, especially on trade and farming. Control measures in China have so far been effective, but at a high price – over 8,000 pigs have been slaughtered in a bid to rapidly contain the outbreak. However, this action is necessary; if ASF were to circulate in such a substantial pig population, neighbouring countries would be at risk as would other parts of the world through global trade and movement of infected pork products by people travelling internationally.

Understanding this disease is now more critical than ever, and Pirbright researchers are working to find out how the virus evades the host’s immune system and how it is transmitted, which will greatly aid the researchers’ ability to develop potential vaccines. Development of a safe and effective vaccine has recently made significant progress through the work of researchers led by Dr Dixon. The team has come up with two promising ways to make ASF vaccine candidates.

In the first study, they modified the ASF virus so that it had a reduced ability to cause infection – known as a live-attenuated vaccine. Pigs that were exposed to the modified strain in a small trial were protected against further infection by a natural ASF virus, indicating this vaccine candidate has potential for further development and trials. The second method involved screening ASFV genes for their ability to produce proteins that create an immune response in pigs, and the team is now looking to insert the most promising genes into a vaccine.