0
Here, former head of the swine diseases department at the National Veterinary Institute of Poland, professor Zygmunt Pejsak, answers questions regarding the spread of African swine fever (ASF) in Europe.
Did the news of ASF reaching Germany surprise you?
To be honest, not at all. In my opinion it was only a matter of the time because we are talking about an infectious disease in free-living animals. We learned in Poland that the ASF virus is spreading slowly but constantly among our wild boar population. A high population density of wild boar in an area facilitates fast ASF spread and some regions in Germany have a very high density.
Why should we expect that the ASF virus will continue to spread into Western Europe?
Unfortunately, the virus may still reach other parts of Europe through the wild boar population. For many reasons the general direction of wild boar movement is to the western territories. Within Europe this has already meant from Russia to Belarus, from Belarus to Poland, and from Poland to Germany. Probably the next move will be from Germany to France and perhaps Luxembourg.
How is the number of wild boar evolving in Europe?
We don't really know how many wild boar we have in different countries. In Poland, we estimated one region to contain 1,000 wild boar, but from intensive hunting we found at least 25,000. What we do know across countries is that the wild boar population is growing significantly, driven by factors including the change to large-scale grain cultivation which gives wild boar a good place to survive and to eat almost year-round. Also important is that people now have less time for hunting as a hobby.
Compared to Europe’s first experience of ASF in the 1960s, what has changed today?
One difference is that the wild boar population density in Europe at that time was considerably lower. Also, the genotype-1 of the ASF virus which occurred during the first epizootics in Europe was not as virulent - the observed clinical course of disease was frequently chronic rather than acute. With the genotype-2 which emerged in Georgia in 2007, the current ASF epidemic in Europe is dealing with an African swine fever virus that is highly pathogenic.
Where the spread of virus depends on the circulation of the wild boar, how fast is it likely to travel?
We have calculated that, under normal conditions in Poland, ASF is spreading among the wild boar population at a speed of three to five kilometres per month. So when we saw an outbreak in an area of the country more than 250 kilometres from other affected regions, this was definitely through human activity, not wild boar.
What should we conclude from Polish evidence that ASF infection had been found in most wild boar carcasses recovered from forests and fields but in few wild boar killed by cars?
A low percentage in wild boar killed by vehicles, in regions affected by ASF, relates to the virus pathogenicity. One or two days after infection, the wild boar suffers a high fever and does not move. For diagnostic purposes the most important are dead wild boar, not live ones. Testing of all dead wild boar found in an area is crucial for evaluating the ASF epidemiological situation. If all dead wild boar test negative, you can be pretty sure that the region is free from ASF. Within the regions of Poland affected by the disease, about 80% of wild boar were ASF positive.
What are the main steps to stop the infection from reaching domestic pigs?
In affected areas there should be active searches for dead wild boar and arrangements made for the disposal of wild boar carcasses as fast as possible in proper and secure ways. Active searching, in my opinion, is very important. On a wider level, the first essential thing is to reduce the wild boar population in the whole of Europe. A second necessary measure is to introduce proper rules on biosecurity in all pig holdings. This means not just on big farms, but also on very small farms. Last but not least, I believe we should be closing down all backyard farms because they represent a real risk if they do not really understand what it means to be biosecure.
What factors have been responsible for the recent rapid rate of spread of infections between European countries?
Although experience from Central and Eastern European countries, and now also from Germany, indicates that wild boar are responsible for the shorter transfer of ASF crossing national borders, in my opinion it is mechanical transfer of material by people or on vehicles that accounts for longer ASF transmission. There are no specific reports indicating ASF transmission via aerosol and a transfer of the virus over a long distance would not be by insects, for example.
The question then is, at what speed could this happen?
I think it is probable that ASF will reach other Western European countries in the next several years. We should always remember that African swine fever spreads slowly, inside farms and among the wild boar population. In Poland the virus has taken more than seven years to cross the country from east to west, yet we had been told it would take only one year to go from border to border. Considering that it took only four years to cross the huge country that is Russia and enter Belarus, then just one year to go from Belarus to Poland, I would say that Poland has controlled the spread of African swine fever very well!
