African swine fever in the Caucasus

remain infective in faeces for at least 11 days and in bone marrow for months. When not protected, ASF virus is rapidly inactivated by sunlight and desiccation. As a result of its tolerance to a wide pH range, only certain disinfectants are effective against the virus. African swine fever affects all ages of pigs, without sex predilection. Pigs become infected mainly through the oro-nasal route after contact with infected pigs or through feeding of virus-contaminated products (swill and garbage waste). In areas where competent vectors of the Ornithodoros tick genus exist, transmission via these vectors can be important for virus persistence in an area. Maintenance of ASF virus in domestic pigs in the absence of Ornithodoros ticks is probably dependant on the existence of large, continuous populations of pigs whose high reproductive rate ensures constant availability of naïve pigs for infection and further spread. Aerosol transmission has been shown to occur only over very short distances. Spread via fomites contaminated vehicles, equipment, instruments, clothing, and even insects – is likely when there are high levels of environmental contamination. Waterborne transmission is most unlikely because of dilution of the virus. The virus is relatively stable in the excretions of infected pigs, in pig carcasses and in some pig meat products and fresh pig meat. The ASF virus is resistant to the decrease of pH which accompanies the meat maturation process, and it is not inactivated by freezing or thawing. The ability of the virus to remain infective in edible products such as chilled meat (at least 15 weeks, and probably longer if frozen) and from three to six months in cured hams and sausages that have not been cooked or smoked at a high temperature has important implications for spread of ASF. Undercooked pork, dried, smoked and salted pork and blood or carcasses/carcass meal derived from pigs in an outbreak or endemic setting must be regarded as potentially dangerous if fed to pigs and/or discarded in communal waste sites where pigs may feed. However, cooked or canned hams are safe, as long as they have been heated throughout to 70°C for more than 15 minutes. After infection with the 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 may remain infected for several months, but do not readily shed virus for more than 30 days. The incubation period varies from 5 to 15 days. Although different serotypes cannot be identifi ed, ASF virus strains differ in virulence, leading to acute, subacute and chronic forms of ASF. Clinical disease is usually peracute or acute, and the morbidity and mortality rates African swine fever in the Caucasus Contributors: Daniel Beltrán-Alcrudo, EMPRES; Juan Lubroth, EMPRES Coordinator; Klaus Depner, EMPRES; Stephane De La Rocque