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  : CP : ASF : Introduction : Nature of the disease : Epidemiological features : Virus survival

Virus survival

 
 


  • In the environment

ASF virus, in a suitable protein environment, is stable over a wide temperature and pH range. It has been shown to survive in serum at room temperature for 18 months, in refrigerated blood for 6 years, and in blood at 37C for a month. Heating at 60C for 30 minutes will inactivate the virus. In the laboratory, ASF virus remains infective indefinitely at -70C but may be inactivated if stored at -20C. In the absence of a protein medium, viability is greatly reduced. ASF virus is generally stable over a pH range of 4 10, but in a suitable medium (serum) has been shown to remain active at lower and higher values for a few hours to three days. Putrefaction does not necessarily inactivate the virus, which may remain viable in faeces for at least 11 days, decomposed serum for 15 weeks, and in bone marrow for months. On the other hand, culture of virus from decomposed samples is frequently unsuccessful.

As a result of its tolerance to a wide range of environmental factors, only certain disinfectants are effective in the control of ASF (see Control).

  • In the host

After infection with ASF virus, domestic pigs may shed infective amounts of virus for 24-48 hours before clinical signs appear. During the acute stage of disease, enormous amounts of virus are shed in all secretions and excretions, and high levels of virus are present in tissues and blood. Pigs that survive the acute disease remain infected for several months, but do not readily shed virus for more than 30 days. As in wild suids, infective levels of virus are found only in lymph nodes, and other tissues are unlikely to contain infective levels of virus for more than two months post infection. The exact length of time over which infective levels of virus are maintained in lymphoid tissues in either wild suids or domestic pigs is unknown, and is probably subject to considerable individual variation.

  • In animal products

The ability of ASF virus to remain infective in edible products such as chilled meat (at least 15 weeks) and 3 6 months in processed hams and sausages that have not been cooked or smoked at a high temperature has important implications for spread of ASF. Undercooked pork, dried and smoked pork and carcass meal derived from pigs must be regarded as potentially dangerous if fed to pigs.