African swine fever originated in Africa, where the virus also has the highest genetic diversity. Starting from there, it has spread to Europe and Asia several times in the course of food transport. African swine fever is currently found in many European countries, some of which are Austria's direct neighbours, in wild boar and sometimes also in domestic pigs. Austria has so far been spared from ASF.

In Africa, different species of porcine animals (bush, forest and warthogs) and ticks of the genus Ornithodoros are the main reservoir of the pathogen. In Europe, this role is taken over by the wild boar.

Transmission occurs either via the bite of infected ticks (at present, this transmission route is not significant in Europe), through direct contact of susceptible pigs with infected conspecifics or their virus-containing body fluids, or through ingestion of virus-containing food waste. Since the virus is very resistant, it remains infectious to some extent even after drying or processing/maturing in raw meat products such as raw ham or salami.

4 to 19 days

The symptoms are strongly dependent on the virus strain. The strain currently present in Europe of the so-called genotype 2 usually leads to highly febrile, severe general diseases in domestic and wild pigs of all ages, in which bleeding into the skin and internal organs can occur. Affected animals usually die from the disease before they develop antibodies. However, there are also virus strains that lead to milder courses of the disease.

There is no therapy

Although vaccination against ASF is being worked on, it is not yet available in Europe. Prevention is therefore limited to early detection, separation and culling of infected animals.

Austria has so far been spared African swine fever, although it does occur in some neighbouring countries such as Germany, Italy, Slovakia, the Czech Republic and Hungary, but also in Poland, the Baltic states (Estonia, Latvia, Lithuania) and many eastern and south-eastern European countries (Romania, Bulgaria, Serbia, North Macedonia, Greece, Moldova, Ukraine, Russia). The main risk for Austria remains the entry from the eastern outbreak areas in Europe.

The Austrian animal disease radar evaluates and compiles information on the international situation and spread of the most important animal diseases that are relevant for Austria. This enables potential risks for Austria to be recognised and communicated at an early stage. The animal disease radar is published monthly.

Since the end of 2019, all wild boar found dead in Austria must be reported and tested for the ASF virus by AGES for the purpose of early detection. In addition, abortions and clinically or pathologically conspicuous domestic pigs are also tested.

African swine fever virus (ASFV) is a DNA virus that is the only virus belonging to the family Asfarviridae, genus Asfivirus. ASFV has a double-stranded DNA genome with a very complex structure, approximately 170,000 to 192,000 base pairs in size. There is only one serotype, but based on the viral p72 gene, 24 different genotypes are currently distinguished. The virus shows a tropism to macrophages and is therefore present in high amounts in the blood and all blood-containing organs (particularly high viral loads are found in the spleen). ASF is a notifiable disease.

Transmission

The transmission route via ticks of the genus Ornithodoros, which was important in Africa and historically also in Europe, does not play a role in Europe according to current knowledge. Domestic and wild pigs become infected through contact with infected conspecifics, ingestion of food waste containing the virus, and possibly through contaminated objects such as farm equipment, vehicles, and clothing. Based on current knowledge, feral pigs that die of ASF or their carcasses are an important source of infection for conspecifics. Early removal of these carcasses is therefore of great importance in the infected area.

Symptoms

The incubation period is 4-19 days The most important symptoms are fever (40.5 °C to 42 °C) and apathy. After the pathogen enters the host, viremia with fever occurs first. Many African wild pigs (e.g., warthogs) are inapparently infected with the virus. Pigs may also carry the pathogen without clinical signs (asymptomatic carriers). Pigs with symptoms show typical clinical signs, which depend on the virus strain. In Europe, ASF virus genotype II is common and usually leads to an acute course of the disease.

There are several forms of progression - depending on the virulence of the pathogen:

Peracute - acute form (usually caused by highly virulent ASF virus, e.g., ASF virus genotype II).

• Fever (40.5 °C to 42 °C)
• Leukopenia and thrombocytopenia (48 to 72 hours)
• Erythema = redness of the skin: ears, tail, distal extremities, abdomen, and chest
• bleeding in internal organs (spleen, lymph nodes, stomach, kidneys, lungs)
• increased pulse rate
• increased respiratory rate
• vomiting
• diarrhea (usually also bloody)
• Death occurs within 6-13 days (up to 20 days). The mortality rate is 90-100% in domestic and wild pigs.

Subacute form (usually due to moderate-virulent ASF virus).

• Symptoms are not as severe as in the acute form; abortions occur more frequently. The course of the disease lasts 5-30 days. Death occurs within 15-45 days. Mortality rate is lower than in the acute form (30-70%).

Chronic form (usually caused by low-virulence ASF virus).

• Symptoms are not as pronounced as in the acute form
• weight loss
• irregular temperature fluctuations
• breathing problems
• arthritis
• chronic skin ulcers partly skin necrosis
• Pericarditis
• adhesion of the lung
• joint swelling
• course of the disease lasts about 2-15 months
• low mortality rate (< 20 %)