SEROLOGIC AND VIROLOGICAL EVIDENCE OF PARVOVIRUS CIRCULATION IN WILD BOARS IN PORTUGAL

Abstract

Wild boars (Sus scrofa) are indigenous species in many countries and can act as reservoirs for important infectious diseases in domestic pigs. The increase in wild boar population observed in several European Countries such as Portugal, Spain, Italy and Germany higher the risk of transmission of diseases between these species particularly in free-ranging production regions. Our objective was to infer about the actual epidemiology of Porcine Parvovirus infection in the wild boar population in Portugal, using tissue and blood samples collected from hunted wild boars for regular monitoring for the presence of exotic notifiable diseases such as Classical Swine fever and African swine fever, in accordance to the national surveillance programs implemented by the Portuguese Veterinary Authorities. A small-scale serological survey using sera of 392 wild boars shot in five of the seven regional agriculture services of Portugal between 2009 and 2010 were tested by a commercial blocking ELISA (Ingenasa) for the presence of PPV antibodies. The overall seroprevalence rate was estimated in 30.9 % and PPV antibodies were detected in animals originating from the five regions studied. The presence of Porcine Parvovirus DNA was tested by real time PCR using primers designed during this study on the NS1 coding region which amplifies a 71 bp long fragment and a TaqMAN probe described by Chen et. al. (2009). PCR tests were performed using DNA extracted from pools of spleen homogenates of up to five animals from the same hunt. The results showed that at least 30.9 % of the samples were positive. The specificity of the detection was further confirmed by sequencing analysis of the amplicons cloned into pCR2.1TOPO TA. Another genomic region, within the VP2 coding sequence, was amplified and sequenced unequivocally demonstrating the presence of Porcine Parvovirus in the tissues. Interestingly, 48.7% of the sera found positive for PPV antibodies were also PPV PCR positive suggesting a longer time viremia in this specie compared to what is described for domestic pigs. Our results clearly show that PPV infection is common in the wild boar population. We estimated that less than 40.3 % of the animals are negative to both PPV Ab and PPV DNA which corroborates the scenario of an active infection, probably with higher incidence in younger animals. Wild boars constitute therefore a possible PPV source of infection for domestic pigs, particularly in areas where the typical Portuguese extensive or semi-intensive type of pig production is practiced in which close contact between the species is observed.