While countries like Denmark are building walls to prevent the spread of African swine fever (ASF), a new mathematical model has identified two effective tactics. A team of scientists in Scotland and Spain has reported that culling and fast removal of animal carcasses are critical for the eradication of the ASF in pig herds.
Prof Andy White and his Heriot-Watt University mathematics research team worked with the SaBio group of the Spanish Game Resources Institute (IREC), UCLM and CSIC (Ciudad Real, Spain) to develop the new model.
Understanding the transmission of ASF
ASF is a highly infectious virus that causes a severe, usually fatal disease in domestic pigs and wild boar. There is no treatment or vaccine. While it is not a threat to humans, the virus can have a profound socio-economic impact on areas with outbreaks.
“African swine fever can rapidly devastate pig populations, and there are outbreaks in China, Poland, Belgium and the Baltic states at the moment,” says Prof White. “In China, it is reported to have wiped out around 40% of the country’s pig population.”
The team’s mathematical model was used to understand the different ways that the virus can be transmitted.
“Wild boar transmit the disease and their numbers are on the rise in Europe. There are several populations in the UK and here too numbers are increasing,” says Prof White.
“To match the data, we showed that infection needed to occur in three ways. Through contact between susceptible and infected wild boar, through contact between susceptible wild boar and infected carcasses, and via individuals that survive the initial infection but succumb to the disease after several months.
Reducing the spread of ASF
The new model also considered biosecurity measures that can help mitigate the spread of an outbreak.
“A combination of culling and the removal of infected carcasses is the most effective way to eradicate the virus without also eradicating the host population,” explains Prof White. “It is important to act quickly as early implementation of these measures will reduce infection levels while maintaining a higher host population density. In some cases, this could prevent the virus from establishing in a wild boar population.”
The model also suggests that it may be easier to control ASF in warmer climates as higher temperatures lead to faster degradation of infected carcasses, which reduces the severity of an outbreak.
In some regions, wild boar are supplementary fed to increase their density. The model suggests this should be avoided when ASF is a threat, as it leads to a more pronounced epidemic outbreak and persistence of the disease in the long-term.