African swine fever (ASF) is caused by a virus, which infects domestic and wild pigs. The disease is endemic in warthogs and bush pigs found in southern Africa as well as domestic pigs in some countries. A type of soft-bodied tick that lives in the animal’s burrows transmits the virus. Infected wild animals do not show any clinical signs; however, in domestic pigs it causes serious disease. As there is no vaccine or treatments available, the general method of eradication is through slaughter policies. Among domestic pigs, transmission can be through consumption of un-cooked, contaminated pork products. The virus can survive for a long time on pig carcasses; curing or smoking does not destroy it. Similarly, it is difficult to remove from the environment.
Transmission of virulent strains results in most animals in a herd becoming ill and the majority dying. Milder strains of the virus are also seen, but they are still a serious issue for infected herds. Pigs develop a high fever and then lose their appetites. Extremities become cyanotic, and hemorrhages appear in the skin and internal organs. The disease can spread very quickly though a herd; animals die between two and ten days after becoming ill, and up to 100 percent mortality is reported. For a definite diagnosis, blood and/or tissue samples need to be sent to a laboratory to distinguish ASF from classical swine fever (CSF).
To date, the European Union has officially confirmed 323 outbreaks of ASF. In 2014 only 10 of cases involved pig farms; the rest were wild boar. All but one of the cases in domestic pigs were on small operations (<200), which are more vulnerable from contact with wild boar. The exception was in Lithuania at one of the country’s largest pig facilities (19,000+ head).
Wild boar appears to be a major vector for transmission of ASF. Cases have been reported in animals from Russia, Belarus, Estonia, Latvia, Lithuania and Poland. In these countries wild boar herds are prolific and populations can move over borders. In December last year the disease was confirmed in wild boar in Belarus, close to the Russian border. In January 2015 there were new outbreaks in Latvia and Poland, and then, in February, there were new reports from Poland. By the middle of March, there had been 72 wild boar cases in Latvia, across 10 regions.
In Russia ASF has been spreading through the wild boar population since 2007 -- hundreds of thousands of commercial pigs have been destroyed as part of control measures. It is believed that wild boar spread the disease in Russia from Georgia in 2007 and it has been travelling through the region ever since. Movement restrictions exist in several regions and millions of rubles have been paid out in compensation. In February last year Russia banned pork imports from the EU following ASF outbreaks in Poland and the Baltic states.
Biosecurity is the first line of defense against ASF and, depending on the country, preventing contact between pigs and wild boar is especially important. This is a particular issue in free-range herds from which wild boar will try to scavenge food. Double-ring fencing is recommended.
ASF is a disease listed on the World Organisation of Animal Health’s (OIE) Terrestrial Animal Health Code and is reportable on identification. Movement restrictions play a vital role in controlling the spread of the disease between countries. These often apply to pork products as well as live animals. For example following the outbreak at one of Lithuania’s largest pig farms, a 3 kilometer protection and 10 kilometer surveillance zones were set up. Controlling wildlife reservoirs is another important measure -- wild boar populations are culled near to any cases in wild or domestic pigs.
All successful eradication programs have involved the rapid diagnosis, slaughter and disposal of all animals on infected premises, thorough cleaning and disinfection, disinsectisation, movement controls and surveillance. These methods have been effectively tested in Sardinia where the disease has been endemic for decades but never spread to mainland Europe.
There have been no more cases in domestic pigs over the winter, but infected wild boar were being reported throughout. The location of these animals suggests that the disease hasn’t spread further into the EU. The Danes are particularly concerned about the spread from Poland and have set up huge truck washes at their borders.
Belarus was particularly hard hit by ASF outbreaks last year, with the pig population dropping by 0.8 million head. However, as a result of ongoing negotiation regarding re-opening trade with Russia and funds for improving facilities, the future is looking hopeful for the industry. However, in Russia itself pork imports were down by 40 percent in 2014. Although, in part due to political unrest, ASF is also to blame. It must not be forgotten that the conflict in Ukraine means in certain areas cases are less likely to be reported or control measures effectively deployed.
Although legislation in Europe forbids the feeding of food waste to pigs, this method of transmission is still a possibility in other regions. Waste from aircraft, ships and other vehicles is an issue, particularly if it has come from Africa. Worryingly in August last year, DNA from the ASF virus was found in cooked sausage produced in Belarus. Russia quickly imposed import restriction on such products, but it shows that this is a potential means of disease transmission in the region. Even staff lunches are under suspicion as a possible risk factor.
Although control measures are helping to reduce transmission of ASF, it has spread further into Europe is a distinct possibility. The German authorities are particularly concerned about the spread of ASF to their pig herds. The country borders several of those already affected with the disease. The focus in Europe is on preventing the diseases being introduced, ensuring vets and producers recognize the symptoms early. The importance of biosecurity is being disseminated and the hunting fraternity enlisted to help control wild boar. Vigilance is essential for the pig industry, as with any disease outbreak there are significant financial implications.