African swine fever is a highly contagious viral infection of pigs, wild boars, and minipigs caused by the ASF virus. African swine fever does not spread to humans. There is no vaccine or treatment for the ASF virus.
African swine fever has never been found in Finland. The disease has been detected in regions close to Finland, and the risk of its spread to Finland has increased.
The incubation period in individual animals is 5 to 15 days. However, in practical conditions, it can take several weeks before the clinical signs appear on a farm after infection. ASF can be an acute, subacute or chronic disease.
In the acute form of the disease a typical early sign is high fever (more than 40,5 °C) accompanied by lethargy, appetite loss, rapid and laboured breathing, and ocular and nasal discharges. Sudden death without preceding symptoms is also typical of the disease. Pigs show neurological symptoms and they huddle together. Abortion can also be a symptom of the disease. Some pigs may also suffer from vomiting and constipation, and others from bloody diarrhoea. Animals have subcutaneous oedema or haemorrhages especially in the extremities and ears. The animal may develop coma before death, which occurs within 1 to 7 days after the appearance of clinical signs. The morbidity and mortality rates on farms may be as high as 100 per cent, but the number of animals presenting symptoms may be significantly lower at first.
It is impossible to distinguish the acute disease from classical swine fever on the basis of signs displayed by the animals. Acute classical swine fever or African swine fever should be suspected every time clearly visible cyanotic skin hemorrhages are detected on the ears and skin of an animal. Very few other diseases cause similar lesions.
The subacute form of the disease is typical in endemic regions. The symptoms of subacute infection include intermittent fever, lethargy and pneumonia. Heart failure may result in death. In the subacute form of the disease the pathological changes are milder than in the acute form. The chronic form of the disease is rare. It can be accompanied by secondary bacterial infections. The clinical signs of chronic ASF can include respiratory problems, abortions, arthritis, chronic skin ulcers or necrosis.
African swine fever can be indicated, among other things, by finding one or several dead wild boars, a living wild boar presenting with symptoms of the disease or a wild boar carcass with unusual hyperaemia upon necropsy.
Since the symptoms and number of animals presenting with symptoms may vary, African swine fever should still be suspected in cases where the animals present with either fewer or milder symptoms.
Diagnosis and samples
In the event of suspected case of disease, the diagnosis is based on rapid detection of symptoms and examination of the infected animals. The disease can be diagnosed either by isolating the virus or detecting its genome in the organs or tissues from dead pigs or by detecting antibodies in the pig serum. The specific instructions on taking samples provided by Finnish Food Authority must be followed.
African swine fever is transmitted by oronasal spread from infected pigs to healthy pigs. Indirectly, the disease spreads, example through the meat, meat products or by-products from an infected animal, from untreated hunting trophies and from food waste containing meat of an infected pig or wild boar. The disease can also spread through equipment, clothes, feed, litter, transport equipment and foods contaminated by the virus. The ASF virus is present in all secretions of an infected pig or wild boar and remains in the blood and in the carcass of a dead pig for up to several months.
In Africa and in areas with vector insects, Ornithodoros ticks in particular, vectors may have a significant role in the preservation of the virus. African wild boars may carry the virus and infect pigs without showing signs of the disease themselves. European wild boars, on the other hand, would become infected and display typical symptoms.
Controlling the disease and prevention
African swine fever is a highly contagious animal disease that requires legislative control. If there are any signs of African swine fever suspected at a farm, it is necessary to immediately inform the municipal veterinarian. If the disease is suspected, an official veterinarian will inspect the pigs and, if necessary, take samples of them for investigation. Based on an official suspicion of an outbreak, the Regional State Administrative Agency may impose restrictions on the farm, for example on the transfer of pigs, in order to prevent the disease from spreading, until the disease can be ruled out. If the disease is found to be present in the pigs, Finnish Food Authority will order the pigs to be culled, the carcasses to be destroyed and the farm to be disinfected. Spread of the disease from the infected farm is prevented by restricting the transport of pigs and pig products with the aid of protection and surveillance zones established around the farm. In addition to the above measures, efforts should always be made to find out where the disease has come from to the farm. In this connection, samples can also be taken from pigs at other farms to establish the situation.
Measures in connection with a suspected or confirmed outbreak of African swine disease are prescribed by the Animal Diseases Act and the Decree of the Ministry of Agriculture and Forestry on the prevention of African swine disease (10/14).
Once the disease has broken out, there is no treatment, and therefore early detection and effective prevention of spreading is important. Maintenance of disease protection on pig farms, and observation of waiting periods after foreign farm visits play a key role in the prevention of the disease. Feeding any type of food waste to pigs is forbidden to prevent spreading of diseases. The disease may spread with live pigs, their gametes and foodstuffs. Therefore it is important that the regulations on import of these are followed carefully.
Access of wild boars to the immediate vicinity of pig farms or farmed wild boars must also be prevented in areas with wild boar stocks. There is no accurate information about the size of the population of wild boars in the wild in Finland: the population has grown in the past few years due to mild winters and extra feeding.
In Finland, monitoring of the disease is based on examination of screening samples from domestic pigs and farmed wild boars, and rapid detection of symptoms and examination of the infected animals. Wild boars have been examined for African swine fever since 2010.
Finnish Food Authority welcomes samples taken from hunted wild boars especially from the areas of the Finnish Wildlife Agency in Uusimaa, South-East Finland and Northern Karelia. It is particularly important to obtain for examination wild boars that have died of their own accord or that appeared to be sick. Even very old and rotten carcasses are worth examining in case of the ASF virus as the virus remains alive in the carcass for a long time. All wild boars found dead should be reported to the local municipal veterinarian as soon as possible.
Research concerning potential entry of the disease in Finland
Finnish Food Authority has published a risk profile on potential entry of African swine fever into Finland. The risk profile describes potential entry routes that could lead to the disease being introduced to Finland. The most essential entry routes include: entry with people who have travelled in the infected area; via infected meat or meat products; with live domestic pigs or sperm; or carried by contaminated animal transport vehicles. Furthermore, it outlines, for example, movements of wild boars and animal transport vehicles; transport of animal-based waste across the border; and potential risk factors related to hunting tourism.
Occurrence in Finland and elsewhere
African swine fever is endemic in Africa. Outside Africa, outbreaks have been detected within the European area in Italy (Sardinia) and the Caucasus region. African swine fever spread to the Caucasus region in 2007 and the efforts to bring it under control have failed in the region ever since.
In the neighbouring areas of Finland, African swine fever was detected the first time in 2009. The outbreak occurred on a pig farm near St. Petersburg in the Leningrad Oblast. After this individual cases of the disease have been found in the environs of Finland on small pig farms on the areas of Murmansk, Arkhangelsk, Leningrad and Russian Karelia. Outside Caucasia, several cases of the disease have been detected in the Tver Oblast.
During 2014, African swine fever spread to Lithuania, Latvia, Poland and Estonia. During 2015, outbreaks have been found in domestic pigs and wild boars in all these countries. Until 2018 African swine fever has been found also in Czech Republik, Romania, Hungary, Bulgaria and Belgium. In 2019, African swine fever spread to Slovakia. The disease has been detected also in Ukraine, Belarus, Moldova and Serbia. In 2020 the disease spread to Greece.
In 2019, Czech Republik was officially released from African swine fever.
In 2018, African swine fever spread to China. In 2019, it has been detected also in Vietnam, Mongolia, Cambodia, Laos, North Korea, Hong Kong, Myanmar, Philippines, East Timor, and South Korea.
No cases of African swine fever have ever been detected in Finland.