African swine fever (ASF) is a highly contagious hemorrhagic disease of viral origin. It affects pigs, both domestic and wild, of all age groups. This illness is caused by a DNA virus of the Asfaviridae family and does not mean a threat for public health. It is endemic in most of the countries of sub-Saharan Africa, although it is also present in regions of Asia and Europe, being endemic only in Sardinia (Italy).

Current state of the African Swine Fever

African Swine Fever has been mainly on the continents of Europe, Asia, and Africa. It is a disease that must be declared to the OIE. Here, we will review the current state of the disease. Besides, Figure 1 shows the most recent map issued by the OIE where you can see the free countries and the affected countries.

In the world, between 2016 and 2020, 14,327 outbreaks of African Swine Fever have occurred, in which there was a loss of 8,202,702 domestic pigs. Adding the 17,938 outbreaks presented in wild pigs, a total of 32,265 outbreaks of African Swine Fever were found.

• Europe

Recently, on October 21, 2020, an outbreak of 5 pigs that died from African Swine Fever was reported in Ukraine. (OIE, 2020). Other countries that have reported cases of African Swine Fever in 2020 are Latvia, Germany, Hungary, Romania, Russia, Ukraine, Latvia, and Moldova.
During the year 2019, Bulgaria reported an outbreak of African Swine Fever on July 4 of that same year, with 222 foci of the disease.
In Slovakia, on July 25 the appearance of the African Swine Fever was reported for the first time in that country, with 40 foci presented.
Between 2016 and 2020, in Europe, there were 4,271 outbreaks of African Swine Fever, in which there was a loss of 1,383,272 domestic pigs. In wild pigs, the continent had 654,809 cases.

• Asia

During 2020, China reported cases of African Swine Fever in October. In the same month, Korea reported a large number of cases of the swine viral disease.
Other countries reporting cases: Philippines, Vietnam, Myanmar, Laos. In the last report made by China, dated in October, African Swine Fever appeared in an outbreak, where 14 pigs became ill, and seven died, thus leaving an apparent fatality rate of 50%.
Between 2016 and 2020, in Asia there have been 9,928 outbreaks of African Swine Fever, in which there was a loss of 6’733,791 domestic pigs. In wild pigs, the continent had 116,430 cases.

• Africa

On the African continent, during 2020, cases of African Swine Fever were reported in the month of October in the following countries: South Africa, Nigeria, Zambia, Ivory Coast, Namibia, Zimbabwe, Kenya, Sierra Leone. In the last report made by South Africa, dated in October, it is reported that the African Swine Fever occurred in two outbreaks, where 17 pigs became ill, and 15 died, thus leaving an apparent fatality rate of 88.24%.
Between 2016 and 2020, there have been 128 outbreaks of African Swine Fever in Africa, in which there was a loss of 85,539 domestic pigs. In wild pigs, the African continent had 61,459 cases.

• America

No cases of African Swine Fever have ever been reported on the continent of America, as the OIE map above showed. However, surveillance systems are alert to the problems that the entry of a new disease like this would mean in these countries. Keeping the continent free from African Swine Fever disease involves robust monitoring and control systems that work to maintain the current status.

Economic importance

This pathology has catastrophic effects on commercial and small-scale pig production in rural populations. The disease implies serious socioeconomic consequences for the subsistence of rural populations. At country level, economic losses are related to the closure of the market options, the reduction of exports, the loss of competitiveness and the costs associated to the control and eradication plans.

What are the origin and development of the African Swine Fever

Oronasal route is the most common pathway for animal infection, although it may also take place by cutaneous, intramuscular, subcutaneous and intravenous route.

Primary replication takes place in the lymph nodes closest to the place of entrance of the virus. During the 2-8 days after infection, it spreads by blood and/or lymph. As the virus reaches different organs, the second replication occurs, which destroys the tissue inside the blood vessels (endotheliums) and causes bleeding.

How is african swine fever transmitted?

The transmission of the disease is complex and depends on several factors: environment, type of production system, management and food, hygiene and biosecurity measures, presence of vectors such as ticks or wild boars.

The routes of transmission include:

• DIRECT CONTACT with other infected pigs (domestic or wild ones). All excretions and secretions of sick animals are a source of infection.
• INDIRECT CONTACT through:
  • Ingestion of contaminated human food (wastes/feed debris or garbage) or infected unprocessed pig meat. Human are healthy carriers of the disease.
  • Contaminated material (i.e. clothing, drinking system, vehicles or footwear).
  • Biological vectors (ticks of the genus Ornithodoros), which are reservoirs of the virus, or rodents.

Which are the symptoms related to african swine fever?

Symptomatology and mortality of the disease varies depending on the viral virulence and the characteristics of the pig (breed and physical condition). European wild boars and domestic pigs show a similar symptomatology. In contrast, African wild pigs usually suffer a subclinical infection, acting as reservoirs of the disease.

The incubation period is of 3 to 21 days, and there are different presentations:

• ACUTE FORM: Caused by highly virulent viruses and characterized by high fever (+40ºC), depression, anorexia, generalized hemorrhages (visible on the skin of the ears, abdomen, distal limbs and tail), cyanosis, abortions, vomiting, diarrhea and death in 6-13 days. Mortality can amount to 100%. Survivors carry the virus for life.
• SUBACUTE AND CHRONIC FORM: Caused by virus of low or moderate virulence. In these cases, the symptoms are less severe, although they may last longer, and mortality is lower (30-70%). Weight loss, intermittent fever, skin ecchymosis, chronic skin ulcers, respiratory signs, arthritis and abortions can be observed.

How is this disease diagnosed?

Presumptive diagnosis can be obtained from clinical signs and lesions evaluation. Although laboratory techniques are necessary to confirm the disease and differentiate it from classical swine fever or from other hemorrhagic diseases of pigs. Laboratory techniques include the detection of the virus or its antigens, or the detection of antibodies against the virus.

How can we prevent african swine fever?

There is currently no effective treatment or vaccine against the disease.

Prevention in disease-free countries is based on implementing a good import policy and biosecurity measures to prevent the entry of infected animals or products. Therefore, it is essential to have a plan for the elimination of food waste from vehicles coming from affected areas and adequate surveillance to prevent the illegal importation of pigs and pork products from affected countries.

Wild pigs play an important role in the transmission of the disease, so a great coordination is necessary between the Veterinary Services and the Forestry Authorities to  be always aware of the density and state of the wild boar population, along with a proper maintenance of biosecurity measures in the pig production systems.

In affected areas or countries, the fight against this disease is based on an early diagnosis and strict sanitary and control measures adapted to the epidemiological situation in the area.

African swine fever is a disease registered in the Terrestrial Animal Health Code of the World Organization for Animal Health (OIE) and is of mandatory declaration. Any suspected outbreak should be notified to the competent authorities.

In farms free of diseases in affected areas, prevention should focus on carrying out an adequate cleaning and disinfection, rodent extermination, control of access to people and vehicles, continuous maintenance of the physical barriers for farm isolation (fences, windows, ventilation systems, walls and ceiling), and control of food and beverage system.

If an outbreak is confirmed, eradication program established by the competent authorities should be applied. Usual measures include:

• Slaughter of all animals of the farm and proper elimination, together with all the residues (feed, bed, clothes or any potential inert vector of the virus). Pits for disposal should be located near the farm to prevent the spread of the virus.
• Disposal of trash bins or containers with human food waste.
• After animals elimination, it should also be perfomed: proper cleaning and disinfection, control of biological vectors such as ticks, and isolation of the farm by fences placing to control the entry of animals and people to the facilities.
• Establishment of a quarantine period before the entry of new animals into the farm.
• Governmental collaboration is essential to ensure the effectiveness of the control plan, as it should: provide training to technicians and owners on measures to be taken and their importance, supply economic compensation to producers affected by the disease, avoid the creation of new uncontrolled farms (especially backyard farming), control of wild boars and control of movements in the affected area.
• Once the affected area has been identified, two action zones are established concentrically, called the protection zone and the surveillance zone. These areas are under movement control from and to the affected area, and animal transport trough the zones is forbidden.

The large-scale epidemic of African swine fever

In 2007, African swine fever was introduced in Georgia and has now spread to several Eastern and Northern European countries. In 2018 the disease crisis spread to Asia.

The large-scale epidemic moved thousands of kilometers away from its original incursion (Georgia) and, in addition to endemic establishment in domestic pigs, the disease eventually invaded wild boar populations. In Europe, from 2014 to 2015 the circulation of this virus in natural ecosystems was already evident and currently the disease is endemic in wild boar populations in several countries and continues to expand its scope in Europe, which is a concern for health authorities.

Controlling this epidemic is a very difficult task for veterinary authorities, given the complexity of the disease, the lack of previous experience, the geographical scope of the problem and its cross-border and multisectoral nature.

At the eighth meeting of the SGE ASF 2017, the World Organization for Animal Health (OIE), the Food and Agriculture Organization of the United Nations (FAO) and the European Union (EU) decided to cooperate in the preparation of a compendium of essential information that provides an evidence-based overview of the ecology of wild boar populations in Northern and Eastern Europe. It also describes practical management and biosecurity measures, which can help countries suffering from large-scale epidemics of this exotic disease.

Mortality rate and clinical signs may vary according to different factors; however, it should be considered that it can reach a mortality rate of up to 100%. This is why this disease is of great medical and economic importance, and the priority it has for its control and eradication, as its effects could be catastrophic for commercial pig production, in addition to forcing the closure of markets, having an impact on exports and on the competitiveness of the exporting country. Despite this, there is no evidence of a risk to public health since it is not a disease that can be transmitted to humans.

The development and approval of vaccines is a long road to travel despite the technology currently available and having an approved vaccine against African Swine Fever is still a project in progress, so prevention is the main method of controlling the disease, mainly in countries free of the disease. This prevention includes the proper disposal of food waste from transnational transportation from affected countries, as well as monitoring the mostly illegal imports of live pigs or products from such countries.

The introduction of the disease into free areas can be avoided by cooking all food waste that the pigs are fed (this applies to commercial units as well as to backyard and pet pigs) and by importing only disease-free pigs.

Control and eradication in countries with this disease can be achieved by the slaughter and proper handling of carcasses of all acutely infected pigs, testing and disposal of all seropositive animals, and good isolation and sanitary practices in the affected herds.

The presence of African Swine Fever is notified to the OIE (World Organization for Animal Health) by its Members through the biannual reports (as sufficiently stable) or through the Immediate Notifications (IN) and Follow-up Reports (FUR), when it is considered an exceptional event.

Between 2018 and the first semester of 2019, this disease was notified through biannual reports in 3 European countries (Estonia, Italy and Lithuania) and 23 African countries. South Africa and Zambia reported the disease in 2018 through biannual reports and through IN and FUR.

A total of 64,446 animals were reported as losses (3,118 losses reported in Report No. 34). In Europe, Bulgaria reported 63,987 losses. In this period, no losses were reported in Asia or Africa.

However, in the period January to March 2020, 22 countries reported new outbreaks through immediate notifications and follow-up reports, 10 in Europe (Belgium, Bulgaria, Hungary, Latvia, Moldova, Poland, Romania, Russia, Slovakia and Ukraine); 8 in Asia (China, Indonesia, North Korea, South Korea, Philippines, Russia, East Timor and Vietnam) and 4 in Africa (Cote D’Ivoire, Kenya, South Africa and Zimbabwe).

NOTE: Russia is mentioned in Asia and Europe, depending on the location of the outbreaks.

In Asia, Myanmar closed its four ongoing outbreaks on December 27, resolving the event in the country. Russia and Korea reported new outbreaks in wild boar.

In Europe, 217 outbreaks were reported: 40 in pigs and 177 in wild boar. A targeted surveillance program is continuing in this region.

Source:

• Centro de Investigación en Sanidad Animal
• OIE, 2020. Reporte de Brote en Ucrania de 2020. https://www.oie.int/wahis_2/public/wahid.php/Reviewreport/Review?page_refer=MapFullEventReport&reportid=36239&newlang=es
• OIE, 2020. Global situation of African Swine Fever. Disponible en: https://www.oie.int/fileadmin/Home/eng/Animal_Health_in_the_World/docs/pdf/Disease_cards/ASF/Report_47_Global_situation_ASF.pdf
• OIE, WAHIS INTERFACE, 2020. Disponible en: https://www.oie.int/wahis_2/public/wahid.php/Diseaseinformation/Diseasedistributionmap?disease_type_hidden=&disease_id_hidden=&selected_disease_name_hidden=&disease_type=0&disease_id_terrestrial=12&species_t=0&disease_id_aquatic=-999&species_a=0&sta_method=semesterly&selected_start_year=2019&selected_report_period=1&selected_start_month=1&date_submit=OK
• Aplicación Oficial de la OIE (OIE-Wahis Alerts) disponible para Android. Consultada el 29 de octubre de 2020.