Towards a vaccine for African Swine Fever
African swine fever (ASF), a highly infectious pig disease, was discovered in China for the first time in August, leading to huge concerns over its potential to spread.
While it doesn’t pose a direct threat to humans, ASF can cause devastation to pig populations and experts have voiced their fears of the risk the outbreak poses to other Asian countries and global pork production. And without a vaccine, it’s a very challenging disease to contain.
We spoke to ASF expert Dr Linda Dixon at The Pirbright Institute, who is leading a team of scientists to develop a vaccine for the disease, to find out more about the disease and their progress.
What actually is ASF?
It was originally discovered in East Africa where there’s a wildlife cycle involving warthogs and a species of soft tick that lives in warthog burrows. It was first noted as a disease in domestic pigs in the 1920s. In 2007, an outbreak moved out of Africa to Georgia from where diseases spread to Russia, Eastern Europe the EU and the latest discovery was in August in China.
One of the issues is that the initial clinical signs are not specific and can be associated with high fever, so it can be difficult to diagnose at early stages. Sometimes the disease is only detected when mortality rate in pigs rises.
How has this disease been spreading?
ASF spreads by direct contact with infected animals or indirectly when contaminated meat or other infected materials are ingested. A challenge with ASF in Europe is the spread in wild boar, which provides a reservoir for infection of pigs and is difficult to control.
One success has been in the Czech Republic where an outbreak in wild boar was detected at an early stage in 2017. The authorities were very quick to identify this outbreak, isolate the infected area by fence, and cull the wild board in this area.
In Poland and the Baltic States, spread of ASF in wild boar is more widespread, so that’s much more challenging to control.
At Pirbright, you’re currently working on a potential vaccine. What type of vaccine are you developing and when might it reach the hands of farmers?
The evidence has been clear that there is good potential to develop a vaccine. The method of using an inactive version of the virus as a vaccine doesn’t work for ASF. It’s a very complex virus, so it’s not an easy route to vaccine development.
The scientific community working on ASF soon recognised that the best chance to develop an effective vaccine was a live attenuated vaccine.
In simple terms, this means we remove genetic material from the virus which prevents activation of the pig’s immune response. Rather than the virus preventing the immune response it is instead activated to efficiently control virus replication and prevent diseases. We also see activation of the ‘memory’ immune response, which provides protection against a future infection.
It is estimated that it will take approximately eight years to achieve the required safety and efficacy, and complete experiments needed to have the vaccine registered. There’s still a long period to go until it’s ready for use in the field, but this kind of timeline is not unusual when developing vaccines.
Do you think ASF could be a candidate for the next global eradication campaign?
It could be possible to control the disease in domestic pigs, but the wildlife cycle in East Africa is more challenging since many warthogs are infected. This situation provides a constant risk of infection for domestic pigs in that region.
Are there steps that we should be taking at a policy level and even at a food production level in terms of understanding pig production that could help us to better manage the disease?
We should support more research into the virus to enable us to develop a vaccine and understand how it’s spread.
Effective control in China to prevent further spread within China and to other countries in Asia will be very important. ASF has been identified over very wide distances and in many different provinces already, so controlling it is difficult.
Plus, raising awareness of ASF and ensuring that good biosecurity is implemented is key along with good preparation of veterinary services. Swill feeding is allowed in a number of countries and it is important this is properly cooked to inactivate any virus present.
How much of a priority is tackling ASF globally, when you compare it with other infectious diseases?
You just have to look at the press to see the priority given to ASF. Introduction of ASF results in imposition of trade restrictions so can result in a high economic impact in affected countries. There are other diseases which are spread globally but a number of those don’t have the same impact on trade. Due to the high fatality, ASF has a high impact on animal welfare and a big socio-economic impact on small scale farmers in Africa and Europe.
Dr Linda Dixon is head of the African Swine Fever Virus Research Group at The Pirbright Institute.
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