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 37°C for a month. Heating at 60°C for
30 minutes will inactivate the virus. In the laboratory, ASF virus
remains infective indefinitely at -70°C but may be inactivated if
stored at -20°C. 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).
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
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.