Epidemiology of classical swine fever in Sardinia: a serological survey of wild boar and comparison with African swine fever

Abstract

A serological survey was carried out to establish the distribution of classical swine fever among wild boar in Sardinia, where that disease and African swine fever have been endemic in free-ranging domestic pigs and wild boar living in the mountainous areas of the province of Nuoro for several years. Blood samples were collected from 4752 wild boar shot during the period December 1988 to January 1992. An overall prevalence of 11 per cent was observed and the almost constant rate of about 9.8 per cent detected in the past three years indicates that the infection is well established. Wild boar seropositive to classical swine fever were found not only in the areas of the province of Nuoro where they share their habitat with free-ranging domestic pigs but also in other areas of the island where contacts between wild and domestic pigs are unlikely to occur. Therefore, transmission from wild boar to wild boar seems to play an important role in the spread and persistence of classical swine fever virus. In contrast, African swine fever virus is probably unable to persist in the wild boar population in the absence of the risk factor represented by their cohabitation with domestic free-ranging pigs infected with African swine fever.

Role of Wild Suids in the Epidemiology of African Swine Fever

“…They excrete virus in similar quantities as domestic pigs (see Table 2). However, some authors have suggested that they are less efficient in transmitting the infection to other wild boars than is the case for domestic pigs (Laddomada et al, 1994).…”

“…This again highlights the importance of virus heterogeneity, as ASF virus expression in wild boar populations may change over time and will, together with other factors, be influenced by the virulence of circulating strains. In Sardinia and Spain, it has been observed that the virus tends to disappear from wild boar populations if there are no subsequent re-infections through contacts with freeranging infected pigs (Laddomada et al, 1994). Therefore, wild boars are considered not to play a major role as a virus reservoir in the absence of free-ranging, infected domestic pigs (Laddomada et al, 1994;Perez et al, 1998).…”

“…In Sardinia and Spain, it has been observed that the virus tends to disappear from wild boar populations if there are no subsequent re-infections through contacts with freeranging infected pigs (Laddomada et al, 1994). Therefore, wild boars are considered not to play a major role as a virus reservoir in the absence of free-ranging, infected domestic pigs (Laddomada et al, 1994;Perez et al, 1998). However, in areas where the disease is actively circulating, where wild boars occur at high densities and where there are contacts with free-ranging pigs, they can represent a serious challenge as disseminators of the virus across different territories.…”

“…The methods of ASF diagnosis in domestic pigs are equally applicable to feral swine and wild boars (Laddomada et al, 1994;Bech-Nielsen et al, 1995). Lesions found at postmortem are typical of ASF, and virus can be detected in tissues and blood.…”

Temporal and spatial patterns of African swine fever in Sardinia

“…In the absence of Ornithodorus ticks, free-ranging pigs are considered the primary reservoirs of ASFV in Sardinia ± whereas wild boars probably play a secondary role (Firinu and Scarano, 1988;Ruiu et al, 1989;Laddomada et al, 1994a). The rough topography of grazing areas ± where pigs may join different herds, the uncontrolled introduction of pigs from unknown sources, and the feeding to pigs of waste food containing pork were considered major factors in the persistence of ASF in Nuoro (Contini et al, 1982;Wilkinson, 1984).…”