Distribution of Porcine Circovirus 2 in Wild Boar in Estonia

Porcine Circovirus 2 (PCV2), member of the Circoviridae family, is globally prevalent virus in domestic pigs and wild boars, causing a group of diseases known as porcine circovirus-associated disease (PCVAD). Given its significant economic impact and potential for interspecies transmission, surveillance in wild boar populations is essential. As to date, no data exist on PCV2 prevalence in Estonian wild boars. The study aimed to assess the seroprevalence of PCV2 in Estonian wild boar populations by age and sex, and evaluate tissue-level histopathological changes and antigen localization to support serological findings. Blood and lymphnode material from wild boars were collected randomly from all Estonian counties (n=433). They were divided into three age groups and subdivided by sex. Detection of PCV2-specific antibodies was performed using ELISA (INGEZIM Circo IgG 11.PCV.K.1®). Histopathological and immunohistochemical (IHC) examinations were conducted on mesenteric lymph node sections using hematoxylin-eosin and PCV2-specific monoclonal antibodies. Statistical analysis was conducted with Python (version 3.13.0, 2024). PCV2 antibodies were detected in 92% of samples, indicating widespread viral exposure. Highest seroprevalence was observed in wild boars aged ≤1 year, followed by 1-2 year and >2 year groups. No statistically significant differences in positivity were found between age groups (p=0.199) or sexes (p=0.453). Histopathology revealed lymphocyte depletion and histiocyte proliferation in lymphoid tissues and IHC examination confirmed PCV2 antigen presence in cytoplasm of lymphocytes and histiocytes. The high seroprevalence of PCV2 detected in Estonian wild boars aligned with findings from other European countries.