African swine fever (ASF) is a highly contagious, generalized disease of pigs caused by an iridovirus that exhibits varying virulence between strains. One form of African swine fever kills adult pigs before any clinical signs are apparent. After an incubation period of 5-15 days, the disease may manifest itself in a number of forms: peracute (animal found moribund or already dead), acute, subacute or chromic. The virus resists inactivation, and can persist in meat up to 15 weeks, processed hams up to 6 months and up to one month in contaminated pens. Recovered pigs may remain chronically infected and excrete the virus for 6 weeks after infection. Contaminated pens and garbage feeding with material from international airports or seaports are documented methods of spread due to the resistance of the virus to inactivation.
African swine fever is endemic in most of Southern Africa, and on the Iberian peninsula of Europe. Since the 1960's, outbreaks have occurred in France, Italy, Malta, Belgium, Holland, Cuba, Dominican Republic and Haiti.
In Africa, warthogs and their associated ticks Ornithodoros moubata porcinus are the reservoir of disease, although the infection is not clinical in warthogs. Outbreaks occur when domestic pigs come in contact with the ticks, rather than from direct transmission from other pigs or warthogs. In Europe, direct transmission is more important as the virus is shed in high concentration in excretions and secretions during the acute phase. Ticks Ornithodoros erraticus on the Iberian peninsula can also be a source of infection.