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African swine fever (ASF) is a highly contagious haemorrhagic viral disease of domestic and wild pigs, which causes serious economic and production losses.
CAUSATIVE ORGANISM
It is caused by a large DNA virus of the Asfarviridae family, which also infects ticks of the genus Ornithodoros.
Although signs of ASF and classical swine fever (CSF) may be similar, the ASF virus is unrelated to the CSF virus.
MODE OF TRANSMISSION
The spread of ASF is complex and varies depending on the environment, types of pig production systems(indoor or outdoor), the presence/absence of competent tick vectors, human behaviour, and the presence/absence of wild pigs.
Mode of transmission may include:
• Direct contact with infected domestic or wild pigs;
• Indirect contact, through ingestion of contaminated material (e.g. food waste, feed, or garbage);
• Contaminated fomites, or biological vectors (soft ticks of the genus Ornithodoros) where present.
RISK TO PUBLIC HEALTH
ASF is not a risk to human health.
CLINICAL SIGNS
Clinical signs and mortality rates can vary according to the virulence of the virus and the type/species of pig:
1. Acute forms of ASF are characterised by;
• High fever, • Depression, • Anorexia and loss of appetite, • Haemorrhages in the skin (redness of skin on ears, abdomen and legs), • Abortion in pregnant sows, • Cyanosis, • Vomiting, • Diarrhoea and death within 6-13 days (or up to 20 days). Mortality rates may be as high as 100%.
2. Subacute and chronic forms are caused by moderately or low virulent viruses, which produce less intense clinical signs that can be expressed for much longer periods. Mortality rates are lower, but can still range from 30-70%. Chronic disease symptoms may include; • Loss of weight, • Intermittent fever, • Respiratory signs, • Chronic skin ulcers and arthritis.
Different types of pig may have varying susceptibility to ASF virus infection. African wild suids may be infected without showing clinical signs allowing them to act as reservoirs.
DIAGNOSIS
ASF may be suspected based on clinical signs but confirmation must be made with laboratory tests, particularly to differentiate it from classical swine fever (CSF). Guidance on diagnostic tests for ASF can be found in the Manual of Diagnostic Tests and Vaccines for Terrestrial Animals.
PREVENTION
Currently there is no approved vaccine for ASF.
Prevention in countries free of the disease depends on implementation of appropriate import policies and biosecurity measures, ensuring that neither infected live pigs nor pork products are introduced into areas free of ASF. This includes ensuring proper disposal of waste food from aircraft, ships or vehicles coming from affected countries and policing illegal imports of live pigs and pork products from affected countries.
During outbreaks and in affected countries, control of ASF can be difficult and must be adapted to the specific epidemiological situation.
Classic sanitary measures may be employed including early detection and humane killing of animals (with proper disposal of carcases and waste); thorough cleansing and disinfection; zoning/compartmentalisation and movement controls; surveillance and detailed epidemiological investigation; strict biosecurity measures on farms.
As observed in Europe and in some regions of Asia, the transmission of ASF seems to depend largely on the wild boar population density and their interaction with low-biosecurity pig production systems. The good knowledge and management of the wild boar population and a good coordination among the Veterinary Services, wildlife and forestry authorities are required to successfully prevent and control ASF.
Depending on the epidemiological situation, the involvement of the soft tick vector should also be considered in the control programme.
Regional distribution
ASF is present in wild and/or domestic pigs in regions of Asia, Europe and Africa,
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