African swine fever (ASF) is one of the 3 most dreaded epidemic diseases of pigs. The other two are swine vesicular disease (SVD) and foot-and-mouth disease (FMD). ASF is dangerous because of its highly infectious nature, variety of means of spreading, high morbidity rate (= percentage of infected swine population becoming ill), high mortality rate and the lack of specific treatment or vaccine.
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Map of Recent & Historical Outbreaks of African Swine Fever ASF: OIE
Clinical effects Diagnosis Spread and control ASF virus
Geographical Occurrence & History of ASF: Africa Europe Italy
ASF outbreaks in AfricaIn recent years African swine fever epidemics have devastated pig herds in the Côte d'Ivoire, Benin, Nigeria, Togo and, most recently, in Gambia, Ghana and Madagascar. The 1999 epidemic in Ghana was finally brought under control by a major surveillance operation, strict border controls, heightened public awareness, and a market value compensation scheme (with World Bank assistance) for slaughtered pigs.
African swine fever is subclinically (without producing disease symptoms) endemic in warthogs in parts of southern and eastern Africa (not South Africa or Zimbabwe). Biting soft-bodied Ornithodoros ticks spread the virus from warthogs to domestic pigs. Other wild African suids (bush pigs and giant forest hogs) are also sublinically affected by ASF, but their role, if any, in the epidemiology of African swine fever is unclear.
Since 1996 the Food and Agriculture Organisation of the United Nations (FAO) has assisted a number of countries in Africa with Technical Cooperation Projects to control and eradicate ASF.
In the first six months of 2001, ASF outbreaks were reported in Benin, the Democratic Republic of the Congo, Mozambique, Senegal and Togo.
ASF outbreaks in Italy
African Swine Fever has been enzootic (endemic) in Sardinia (classical swine fever has also been enzootic there). Most outbreaks have been in the province of Nuoro, but Cagilari has also been affected. Antibodies to the virus have been found in the local wild boar population.
2010 EU Report on African Swine Fever (ASF) Outbreaks - Sardinia, Italy: News
Clinical effects of ASF
Incubation period is 5-15 days, followed by one or (usually) more of these forms of disease:
Infection with highly virulent virus strains can result in some pigs being suddenly found dead, or close to death.
There is fever (pyrexia), loss of appetite (anorexia) and inactivity. Areas of red or blue skin discoloration may appear on the ventral chest or abdomen, tips of ears or tail, or distal limbs. Diarrhoea, vomiting, coughing, breathing difficulty and abortion may also occur. Almost 100%. of pigs with these symptoms will die within 7 days. Pigs that recover can be lifelong carriers of virus.
Seen particularly with virus strains of moderate virulence. Affected pigs are only mildly ill, but sows may abort. There can be intermittent fever for up to one month, followed in most cases by recovery. Mortality ranges from 30-70%. Recovered pigs can still be excreting the virus up to six weeks after infection.
Although having occasional episodes of fever, these pigs show little illness apart from reduced growth, stunting or emaciation. There may be necrotic patches of skin or chronic skin ulcers. They are vulnerable to secondary infections, pneumonia and lameness (arthritis). Infection lasts for two to five months but mortality is less than 30%.
Diagnosis of African swine fever
Petechial (pinpoint) haemorrhages are very typical, especially in the cortex, medulla and pelvis of the kidneys, the mucous membranes of the larynx and bladder and on visceral surfaces of organs.
Lymph nodes are enlarged and haemorrhages may be seen in the gastrohepatic and renal lymph nodes.
haemorrhagic swollen lymph node - medial retropharyngeal
(courtesy of Dr. Stan Done, Veterinary Laboratories Agency UK)
Blood splashes (ecchymoses) may be present in the skin of the legs or abdomen. The spleen is often enlarged and there can be excess fluid in the abdominal, pleural and pericardial cavities. Oedema of the gall bladder and mesentery of the colon is also quite typical of ASF. In chronic cases, lungs may show focal lesions of caseous necrosis and even mineralisation.
African swine fever is very similar to classical swine fever (hog cholera) and porcine dermatitis and nephropathy syndrome (PDNS) in clinical signs and autopsy lesions. These diseases must be distinguished by means of laboratory tests, such as virus isolation, serology, or a direct fluorescent antibody test on diseased tissues.
Virus isolation from serum, spleen, kidney or lymph nodes.
Virus antigen demonstration by direct immuno-fluorescence on tissues.
PCR (polymerase chain reaction) is a sensitive test to detect viral genetic material.
Serological (antibody) tests on serum from recovering pigs, 8-21 days after infection: ELISA, indirect fluorescent antibody test, immunoblotting, immunoelectrophoresis.
Other pig diseases that can show superficially similar signs to ASF are erysipelas, pasteurellosis, acute Salmonella infection and septicaemia.
African swine fever virus (AFSV) is a DNA virus, formerly classified as an iridovirus (Iridoviridae ) it has recently been re-classified into a newly created family of viruses called Asfarviridae - a name derived from "African Swine Fever And Related Viruses" Within that family it has been allocated to the Genus Asfivirus of which it is the only member.
Different strains of AFSV vary in their ability to cause disease, but they there is one serotype of the virus detectable by blood antibody tests.
Epidemiology and Control of ASF virus
Spread is by pig to pig contact, mechanical carriage by humans or equipment, contaminated injection needles, ticks (and other biting insects and lice) or uncooked swill (garbage).
High concentrations of ASF virus are shed in secretions and excretions from acutely infected pigs. The virus survives well in the environment and in meat, so spread can occur via contaminated livestock pens or by feeding poorly cooked garbage (particularly waste food from the catering areas of international airports or seaports).
There is no effective treatment or vaccine for ASF, so during outbreaks it is vital to slaughter infected herds rapidly and dispose effectively of carcases and litter. Pens and equipment must be thoroughly cleaned and disinfected before re-stocking. It is usual to designate an infected zone around outbreaks in which pig movements are banned or controlled. A surveillance operation is mounted to identify any other infected herds in the area, combined with tracing and testing of all contacts with infected herds.
Border and importation controls need to take into account that live pigs, semen, embryos and products of pig origin all pose a risk of introducing ASF.
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