The origin of African swine fever is in Africa, where the virus also shows the highest genetic diversity. From there, it spread several times to Europe and Asia in the course of food transports.

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 (wild) 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. Prevention is therefore limited to early detection, separation and culling of infected animals.

Austria has so far been spared from African swine fever, but it occurs in some immediate neighboring countries such as Slovakia and Hungary, but also in Belgium, Poland, the Baltic States, eastern Germany and some southeastern European countries (Romania, Bulgaria, Moldova, Serbia). On January 5 and 7, 2022, the first cases of African swine fever occurred in feral pigs in northern Italy. While genotype I has been endemic in Sardinia for decades, African swine fever is now appearing on the Italian mainland for the first time. In May 2022, cases in feral pigs were also reported in Rome. The main risk for Austria remains entry from the eastern outbreak areas in Europe.

In the Austrian animal disease radar, information on the international situation and spread of the most important animal diseases and epizootics relevant to Austria is assessed and compiled. In this way, possible risks for Austria can be identified and communicated at an early stage. The animal disease radar is published monthly.

In Austria, since the end of 2019, for the purpose of early detection, all feral pigs found dead must be reported and examined by AGES for the ASF virus. In addition, an examination of abortions as well as of clinically or pathologically conspicuous domestic pigs is also carried out. In 2021, 1,519 domestic pigs were examined by official order, only a fraction of which took place in the course of exclusion examinations. In the same year, 1,813 wild boars were examined for the ASF virus. In none of these cases was the virus detected.

African swine fever virus (ASFV) is a DNA virus that is the only virus belonging to the family Asfarviridae, genus Asfivirus. The ASF virus has a double-stranded DNA genome with a very complex structure, which is 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. 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 agricultural equipment, vehicles and clothing.

Symptoms

The incubation period is 4-19 days The main symptoms are fever (40.5°C to 42°C) and apathy. After entry of the pathogen into 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). Symptomatic pigs show typical clinical signs, which depend on the strain of the virus.

There are several courses - depending on the virulence of the pathogen:

Peracute - acute form (usually caused by highly virulent ASF virus).

• Fever (40.5 °C to 42 °C)
• Leucopenia and thrombocytopenia (48 to 72 hours)
• Erythema = reddening 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 bloody)
• Death occurs within 6-13 days (up to 20 days). The mortality rate is 90-100% in domestic and wild pigs.

Subacute form (mostly caused by 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. The 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, sometimes skin necrosis
• pericarditis
• adhesion of the lung
• joint swelling
• course of the disease lasts about 2-15 months
• low mortality rate (< 20 %)