Seroprevalence and risk factors of leptospirosis in wild boars (Sus scrofa) in northern Italy

Wild boar (Sus scrofa) is considered a potential source of several viral and bacterial pathogens that represent a risk to humans and other mammals. Among these the spirochete of the genus Leptospira causes Leptospirosis, a neglected zoonotic disease. This study investigates the presence of antibodies against pathogenic Leptospira spp. serovars in wild boar in different areas of the Lombardy region (northern Italy) and the risk factors associated with its presence in a specific population. Blood and tissue samples from wild boars were collected from 2008 to 2013 during a wildlife survey. A total of 2101 serum samples were analysed using a microscopic agglutination test (MAT) to detect antibodies against Leptospira interrogans sensu lato. Culture isolation and Leptospira DNA detection by PCR were carried out using 189 kidney and 159 urine samples, respectively. Antibodies against 5 serovars were detected in 321 serum samples (15.3%). Bratislava was the most frequently identified serovar (14.6%; 95% C. I. 13.1-16.2%), followed by Copenhageni (1.48%; 95% C. I. 1.0-2.1%), Grippotyphosa and Pomona (0.48%; 95% C. I. 0.23-0.87%), and Canicola (0.05%; 95% C. I. 0-0.3%). Genotyping by multilocus sequence typing and multilocus variable number tandem repeat analysis of a single leptospire isolate confirmed the presence of L. interrogans serovar Bratislava with the same genetic profile as Jez Bratislava. The statistical analyses confirmed the wild boar's age class as an important risk factor for the seroprevalence of leptospirosis, whereas no effect of wild boar abundance on seroprevalence was observed. In addition, an increasing seroprevalence was observed, in particular that of Australis Bratislava showed a general increasing pattern over the years. Our results confirmed that wild boars are a potential source of pathogenic Leptospira spp., which can infect humans, domestic animals and other wild animal species in low-density regions, such as those on the Alps.