The illegal rearing and slaughtering of pigs in the wild on the Mediterranean island of Sardinia favor an increase in the biomass of Trichinella britovi in wild boars (Sus scrofa) but do not affect the serological prevalence of infection

Abstract

Abstract Background Worms of the nematode genus Trichinella are zoonotic pathogens with a worldwide distribution. The first report of Trichinella on the Mediterranean island of Sardinia was for Trichinella britovi, one of the four species of this genus circulating in Europe, which was identified in 2005 following an outbreak of trichinellosis in humans due to the consumption of pork from pigs reared in the wild. Since then, T. britovi larvae have been repeatedly isolated from free-ranging pigs, foxes (Vulpes vulpes) and wild boars (Sus scrofa) sampled in the central-eastern region of the island (Orgosolo municipality), but have never been isolated from samples from other areas of the island. The aim of this study was to investigate the parasitological and serological prevalence of T. britovi infection in wild boars in Sardinia over space [eight wild boar hunting management units (HMUs)] and time (seven wild boar hunting seasons). Methods Muscle and serum samples of boars killed in the 2014–2015 to 2020–2121 hunting seasons were collected from eight HMUs of central and south-western Sardinia. Trichinella sp. larvae were detected by artificial digestion of predilection muscles. A total of 4111 serum samples of wild boar were collected from the investigated HMUs and tested by enzyme-linked immunosorbent assay as a screening test and by western blot as a confirmatory test using excretory/secretory antigens. Results Trichinella britovi muscle larvae were detected in six (0.03%) of the 17,786 wild boars tested. All of the Trichinella sp.-positive wild boars had been hunted in Orgosolo municipality (central-eastern area of the island), except for one, hunted in a neighboring municipality. An overall serological prevalence of 3.8% (95% confidence interval, 3.3–4.5) was detected by western blot. No statistical differences were detected between the HMUs where T. britovi larvae were detected in wild boars, foxes, and free-ranging pigs and those where wild boars, foxes and free-ranging pigs tested negative. Conclusions The serological prevalence did not vary between the wild boar populations in which the larval load was detectable by artificial digestion (Orgosolo municipality) and those in which the larval load was below the detection limit. Furthermore, the serological prevalence of anti-Trichinella immunoglobulin G in the wild boar populations remained constant during the study period, which covered seven wild boar hunting seasons. As the transmission events (i.e., the serological prevalence) are stable, the high biomass of the parasite in Orgosolo municipality can only have arisen as a consequence of factors independent of its natural cycle, i.e., the presence of a high number of free-ranging pigs, and the concomitant presence of African swine fever, due to illegal pig slaughtering in the field. This epidemiological situation suggests that the natural cycle of T. britovi may be influenced by inappropriate pig husbandry and slaughtering practices. Graphical Abstract