Serological and immunohistochemical study of African swine fever in wild boar in Spain

Abstract

A serological and immunohistochemical study of African swine fever was carried out in wild boar killed in seven municipalities in the north of the province of Córdoba during two hunting seasons (1991-92 and 1992-93), when the area was affected by the disease. Fourteen of 147 wild boar analysed by ELISA and immunoblotting had antibodies to African swine fever virus. The immunohistochemical study revealed that four cases (two seropositive and two seronegative) showed immunoreactivity to the anti-VP73 monoclonal antibody. Two of the VP73+ wild boar had severe generalised haemorrhages consistent with the acute from of the disease, and another had lesions consistent with subacute African swine fever, but none of the remaining 144 animals had gross or microscopic changes suggestive of the disease. These results indicate that wild boar can suffer from African swine fever without showing clinical signs. The disease in wild boar was associated with the disease in domestic pigs. Thus, no African swine fever-positive boar were found either in one municipality with no out-breaks in domestic pigs or in three municipalities with only one outbreak in pigs during the hunting seasons and during the previous year. These results suggest that European wild boar do not play an important role as carriers of the virus of African swine fever.

Role of Wild Suids in the Epidemiology of African Swine Fever

“…This species is highly susceptible to both natural and experimental infection (McVicar et al, 1981); in the Iberian Peninsula, it perished in large numbers following initial introduction of ASFV (Wilkinson, 1989). Depending on the virulence of circulating strains, some animals survive, and positive animals have been detected during serological surveys (Perez et al 1998). In Florida, it was observed that feral pigs were extremely susceptible to domestic pig isolates from the Dominican Republic (McVicar et al, 1981).…”

“…However, several years later, the number of seropositive animals increased to 10% in some areas and seropositivity levels coincided with areas where domestic pigs remained infected (Perez et al, 1998), suggesting that the initial virulent virus had become attenuated. 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). 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.…”

“…In the Caucasus, proposed methods of control are separation of feral and domestic pigs, and disposal of carcasses and offal from domestic pigs and hunted wild boars, in order to prevent their consumption by free-ranging domestic or wild pigs (Beltran Alcrudo et al, 2008). Obtaining wildlife samples with the collaboration of hunter's associations has proven to be an efficient means for monitoring the disease in wild boar populations (Perez et al, 1998;Arias and Sanchez-Vizcaino, 2002).…”

African swine fever: how can global spread be prevented?

“…Evidence of ASFV infection in wild boar was reported from the Iberian Peninsula (Wilkinson 1984;Arias & Sanchez-Vizcaino 2002), Sardinia (McVicar et al 1981;Laddomada et al 1994;Mannelli et al 1997) and most recently in Russia (OIE WAHID 2009). In areas where domestic pigs were free of the disease, very low prevalence or absence of seropositive wild boars was reported (Perez et al 1998) suggesting limited persistence of the virus in wild boar populations without contact with infected domestic pigs (Laddomada et al 1994;Perez et al 1998;Ruiz-Fons et al 2008). Given the recent development in the Caucasus region and the current situation in Sardinia further research is needed to elucidate the competence of wild boar to act as infection reservoir, and needs to consider potential differences in virulence of ASFV strains.…”