What is african swine fever?
How to prevent? How is it transmitted? What are the signs? How is it diagnosed?
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).
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 blog describes the pathologies that can be found in birds and swine all over the world. This section provides an information about the causes and effects of the main diseases that affect these sectors. This blog introduces the main approaches to avoid frequent diseases, describes the pathologies and visualizes through the photos, also offers knowledge of a very important subject in the poultry / swine sector. The blog is directed by a scientific group of Biovet S.A.