Trichinella britovi outbreak in north-west Italy, 2019-2020: beware of wild boar

Abstract

Purpose: Trichinellosis, a foodborne zoonosis due to nematodes of the genus Trichinella, usually occurs in form of outbreaks following the consumption of untreated meat. Sport hunted wildlife is an increasing source of human cases at the global scale, though North Italy has been rarely involved. We report here a wildlife derived trichinellosis outbreak which spread throughout an entire alpine valley. Methods & Materials: We retrospectively included 96 outpatients referred to the Infectious Diseases Hospital “Amedeo di Savoia”, Torino, North Italy between December 20th, 2019 and January 15th, 2020 after consuming raw sausages from a wild boar of unknown age hunted nearby the village of Chiomonte, in the Susa Valley, 63 Km away from Torino, on November 5th, 2019. Clinical, demographic and laboratory characteristics were recorded at the time of presentation. IgG serology for Trichinella was performed by immunoblot (Trichinella E/S IgG kit, Effegiemme, Milan, Italy). Results: In our cohort we found that 47% of patients were symptomatic, with an uncertain median time from consumption of raw sausage to symptoms and a median time from symptoms to presentation at clinic and serology testing of 14 (IQR 11.75) days. Peripheral blood eosinophilia >500/cmm and CK alterations were found in 26% and 24% of our cohort, respectively. IgG serology was resulted positive in 48/96 (50.0%) of the patients, allowing a diagnosis of confirmed Trichinella spp. infection, later identified as britovi. Only two patients required hospitalization, and no patient suffered serious consequences. Conclusion: We describe in this report the main features of the largest trichinellosis outbreak ever registered in Piedmont region. No major characteristics in clinical, laboratory or serological data were highlighted. Most likely, patients were infected after eating meat products from a single animal, given the very low prevalence of the infection in wild boars in the area. No autochthonous human case has ever been detected in Torino province, and a single wild boar has tested positive for Trichinella since official active surveillance was implemented in 2013. This outbreak should raise attention on the preventive key role of epidemiological veterinary surveillance, and the need to optimize sampling procedures and targeted health education