African Swine Fever Virus (ASFV) is the causative agent of African swine fever (ASF). The virus causes a haemorrhagic fever with high mortality rates in pigs, but persistently infect its natural hosts, bush pigs, warthogs and soft ticks of the genus Ornithodoros, with no clinical signs and symptoms . They act as vectors.
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ASFV is a large, double-stranded DNA virus which replicates in the cytoplasm of infected cells and belongs to the family of Asfarviridae
ASF virus also survives well under most environmental conditions (2-3 months in carcases and in farm sheds). It can survive for many months in meat (3 months in ham, 6 months in brown bone marrow of ham, 18 months in blood meal). It resists to freezing process but is inactivated by high temperature (30 min exposure at 60 °C)
Survival time of the African Swine Fever Virus
Image source: Food and Agriculture Organization
The severity and distribution of the lesions also varies according to virulence of the virus. Severe cases of the disease are characterized by high fever and death in 2-10 days on average. The mortality rate can be as high as 100%. Other clinical signs may include loss of appetite, depression, redness of the skin of the ears, abdomen, and legs, respiratory distress, vomiting, bleeding from the nose or rectum and sometimes diarrhoea.
Bleeding in Kidney & muscles
Image Source : Wikivet.net / African Veterinary Information Portal (AfriVIP) / Sanidadanimal.info
Moderately virulent forms of the virus produce less intense symptoms though mortality can still range from 30-70%. Chronic disease symptoms include loss of weight, intermittent fever, respiratory signs, chronic skin ulcers and arthritis.
Haemorrhages occur predominantly in lymph nodes, kidneys, and heart; haemorrhages in other organs are variable in incidence and distribution. Some isolates produce an enlarged and friable spleen; straw-coloured or blood-stained fluid in pleural, pericardial, and peritoneal cavities; or oedema and congestion of the lungs. Some viruses of low virulence have been isolated in Europe and produce nonspecific clinical signs and lesions. Chronic disease is characterized by emaciation, swollen joints, and respiratory problems. This form of the disease is rarely seen in outbreaks.
ASF cannot be differentiated from classical Swine Fever (hog cholera) by either clinical or post-mortem examination. Samples of blood, serum, spleen, tonsil, and gastrohepatic lymph nodes from suspected cases should be submitted to the laboratory for confirmation.
Prevention and Control Measures :
There is no treatment or vaccine for African Swine Fever. Prevention is through tight Biosecurity measures. Prevention in countries free of the disease depends on stringent import policies, ensuring that neither infected live pigs nor pork products are introduced into areas free of ASF.
In endemic areas, it is difficult to eliminate the natural reservoir in warthogs; however, control of the soft tick vectors is important in preventing the disease. It is also important to ensure that meat from warthogs or infected animals is not fed to susceptible pigs. All successful eradication programs have involved the rapid diagnosis, slaughter and disposal of all animals on infected premises, thorough cleaning and disinfection, movement controls and surveillance.
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