Leptospira Seroprevalence in Bardigiano Horses in Northern Italy

SIMPLE SUMMARY: Leptospirosis is one of the most widespread zoonoses worldwide and is considered a re-emerging disease. In horses, leptospiral infection frequently does not result in a systemic disease and it is commonly believed that horses play a minor role in spreading the disease, compared to other livestock and wild animals. However, horses can become carriers and it has been suggested that the horse is the maintenance host for serovar Bratislava. Epidemiological data regarding leptospirosis in horses in Europe are lacking and further studies are required. The aim of this study was to evaluate Leptospira seroprevalence in Bardigiano horses living in the Province of Parma, Northern Italy, and to identify risk factors associated with seropositivity. A high seroprevalence against Leptospira spp. among Bardigiano horses and a high number of infected farms were found. Unexpectedly, seroprevalence was considerably higher compared to similar studies carried out in Italy. The location of the farm and the type of housing did not affect seroprevalence, but rodent control might reduce the risk of exposure for Bardigiano horses. Horses living in the considered area have high-risk exposure to different serovars of pathogenic leptospires and could contribute to the maintenance of the bacterium in the environment. ABSTRACT: A cross-sectional study was carried out in Bardigiano horses in the Province of Parma, Northern Italy, to assess the seroprevalence of Leptospira spp. and to investigate risk factors associated with the infection. A representative sample of 134 horses from 43 farms was selected by stratified systematic randomization. Blood sera were examined by MAT for the presence of antibodies against seven Leptospira serovars. Ninety animals (67.2%; 95% Confidence Interval 63.2–71.1) and 41 farms (95.3%; 95% CI 92.2–98.5%) were found positive to at least one of the serovars. The most frequently detected reactions were against serovar Bratislava (41.8%), followed by Canicola (36.6%), Tarassovi (28.4%), Copenhageni (17.9%), Pomona (10.4%) and Hardjo (2.2%). None of the sera reacted against serovar Grippothyphosa. Forty-eight horses (53.3% of the seropositives) were positive for more than one serovar and 21 (15.7% of the seropositives) had serum titres ≥ 1000. Bratislava was the serovar providing the highest antibody titres. Prevalence was significantly higher between adult horses and in farms lacking rodent control (p = 0.006 and p = 0.025, respectively). No significant gender or housing-related difference in seroprevalence was found. The anamnestic data suggest that the infection in Bardigiano horses is subclinical in most of the cases. The high seroprevalence indicates that Bardigiano horses living in the investigated area are at high risk of exposure and infection by Leptospira spp.