A RETROSPECTIVE SEROSURVEY OF THREE PORCINE CORONAVIRUSES AMONG WILD BOAR POPULATION IN CAMPANIA REGION

The growing interest in porcine coronaviruses (CoV) is due to both their negative impact on the swine industry and their propensity to mutate and overcome host barriers. A total of six viruses belonging to this family can infect pigs and mainly cause respiratory and intestinal diseases. Among them, Porcine Epidemic Diarrhea Virus (PEDV), Transmissible Gastroenteritis Virus (TGEV) and Porcine Respiratory Coronavirus (PRCV) are widely distributed and frequently reported in Europe [1]. Since information on CoV in wild boar is limited, especially in Italy, a serosurvey was conducted to assess the epidemiological situation in the Campania region and to clarify the role of wild boar as a reservoir for enteric and respiratory porcine CoVs. During the 2016-2017 hunting season, serum samples were collected from 434 feral pigs (from 119 hunting areas in four provinces) and analyzed for antibodies to PEDV, TGEV, and PRCV using specific and commercial ELISA assays. The most common pathogen in our study was PEDV with a percent positivity of 3.83% (CI 95%: 2.05 - 5.6; odds ratio: 5.85 vs. TGEV and PRCV), while very low seroprevalence was detected for TGEV and PRCV (0.67%; CI 95%: 0 - 1.44 in both cases). The combined prevalence was 4.73% (CI 95%: 2.76 - 6.7). Only two wild boars were co-infected, the first with PEDV and TGEV, the second with TGEV and PRCV. Surveys conducted in other European wild boar populations revealed low prevalence values; for example, seroprevalences of 0.7% for PRCV and 0.4% for TGEV were found in Croatia. In Germany, a large-scale survey of 1,221 blood samples found 7.87% PRCV-positive and 1.59% TGEV-positive feral pigs. In Slovenia, a PRCV seroprevalence of 3% was described, although a very high seroprevalence in domestic pigs (65%) was reported. In a study conducted in the Czech Republic, only 1% of the wild boars tested had antibodies to TGEV. In Poland, PEDV seroprevalence was found to be 3.2%, while the virus was not detected by the RT -qPCR assay [2]. These data suggest that CoV infections are not widespread in European wild boar. Considering the very low seroprevalence observed in our study, TGEV and PCRV were not included in the statistical analysis of risk factors. The PEDV prevalence of infected animals was positively correlated with age (0 - 12 months old) (7.2%; CI 95%: 2.89 - 11.49), while univariate analyzes showed no correlation between PEDV seropositivity, sex (P=0.8473) and location (p=0.66), although a higher prevalence was observed in female wild boar (4.4%; CI 95%: 1.21 - 7.55) and in Avellino province (4.8%; CI 95%: 0.21 - 9.31). The lack of correlation between positivity and sex is an unexpected result, since close contact between sows and piglets (which are the main vectors of the virus) should increase the risk of exposure for females. Conversely, we observed a statistical correlation between age and PEDV seropositivity. Indeed, the highest seroprevalence (7.2%) was observed in young animals (< 12 months), with a decreasing trend of seroprevalence in the three age groups tested (young animals = 7.2%, subadult animals = 3.7%, adult animals = 0%). The absence of positive adult animals could be explained by the short duration of circulating detectable antibodies, which is typical for CoV [3]. The low prevalence detected in our study suggests that these viruses are not widespread in the wild boar population in the Campania region and do not represent a concrete risk for CoV transmission to domestic pigs. Considering the regular epidemics reported in the swine industry, we can assume that these infections have obvious effects only when predisposing factors typical of intensive farming (such as stress, overcrowding, etc.) induce higher susceptibility and ensure wide dissemination.