Porcine circovirus 3 subclinical infection in wild boar is not associated with systemic lesions

Abstract

Porcine circovirus 3 (PCV3) is known to endemically circulate in domestic pigs, both in intensive and extensive settings. This virus occasionally causes reproductive and/or postnatal disease, although its full impact is currently undetermined. The appearance of such diseases is most remarkably correlated with the presence of vascular lesions consisting of periarteritis in medium and small calibre arteries, which are found in many tissues, but are most consistently and abundantly detected within the mesenteric arterial plexus. Multiple studies demonstrated PCV3 high prevalence in wild boar (Sus scrofa) as well, which poses a risk as a potential wildlife reservoir. Nevertheless, no studies have specifically tackled the potential pathogenic role of PCV3 in wild boar populations. In this study, we evaluated the presence of periarteritis in a large number of tissues (mostly mesenteric plexus) from wild boar necropsied as part of a disease-monitoring program in Catalonia (northeastern Spain). The presence of PCV3 genome was evaluated by PCR (in serum samples) and in situ hybridization (ISH) (in tissues). While PCV3 presence was confirmed in 26 out of 87 (29.89%) serum samples, none of the tissue samples displayed histopathological lesions compatible with PCV3-associated disease (PCV3-AD). Moreover, ISH revealed PCV3 genome in lymphoid follicles in 4/6 studied cases (in which lymphoid tissue was available), and only one animal displayed mild arterial labelling despite absence of histological lesions. The lack of evidence of lesions associated to PCV3 in wild boar is probably related to ecological and epidemiological factors, which greatly differ from domesticated populations. Therefore, we hypothesize that the occurrence of PCV3-AD in wild boar is highly unlikely, with low or negligible impact on its populations.