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In the Covid-19 pandemic context, several studies have been focused on detecting which animal species can be a potential reservoir for SARS-CoV-2. Pigs represent a species reared worldwide for food production and they have already been shown to be susceptible to six swine specific species of coronaviruses.
Objective: In this study, which is included in the research activities of a broader European project, a cross-sectional and a longitudinal study were conducted on a total of 18 pig farms in north-eastern Italy in order to investigate the epidemiology of specific and emerging coronaviruses in the pig population.
Methods: The detection of the different viral species was carried out through a "nested-RT-PCR pan-CoV" protocol targeting the RdRp gene, subsequently sequenced to identify the viral species and to perform viral phylogenesis. The epidemiological study was conducted to assess the association of prevalence data with some risk factors at farm (structural and managerial) and animal level; the analytical part was conducted firstly by means of univariate analysis and finally building a multivariable model, with the site of sampling (farms) included as the clustering factor.
Results: No samples were identified positive for SARS-CoV-2, suggesting that pigs do not play an epidemiological role in the spread of this virus.
Although with a generally low prevalence, two viral species were detected, PHEV (porcine hemagglutinating encephalomyelitis virus) and PRCOV (porcine respiratory coronavirus). For both these viruses, prevalence was found to be associated with the type of production and farm size, either with the univariate approach, or in the multivariable model. A seasonal trend in prevalence was also identified, with a peak of cases in the summer for PHEV and in the winter for PRCOV, but, due to the small number of farms that has been sampled, further studies will be necessary to make these findings more robust.
Conclusion: The absence of evident clinical signs at the time of sampling, as well as the low genetic variability of the circulating strains observed by the phylogenetic analysis, may indicate that the two viruses are in an endemic situation.