Equine Salmonella in Argentina: Genetic relatedness with humans and other animal species and first detection of serovar Freetown

Abstract

Salmonellosis in horses can cause severe enteritis with diarrhea, fever, and colic, which is usually severe in foals and hospitalized or immunocompromised animals. Carrier horses may intermittently shed Salmonella, thereby acting as a source of infection for other animals and humans. The aim of this study was to investigate the occurrence and molecular subtyping of Salmonella spp. in horses from Argentina, focusing on potential zoonotic relevance. Only a single isolate (S. Newport) was obtained from fecal samples of 249 clinically healthy horses (2018-2022), indicating a very low carrier detection rate (0.4%). Additionally, 13 isolates from horses with clinical signs of salmonellosis (2006-2017) were analyzed, which comprised S. Typhimurium (n = 9), S. Newport (n = 2), S. Oranienburg (n = 1), and S. Freetown (n = 1). Pulsed-field gel electrophoresis (PFGE) revealed genetic diversity among Salmonella serovars, including clonal outbreaks of S. Typhimurium in a hospital. Comparative analyses using the National PulseNet database demonstrated that many equine isolates shared indistinguishable PFGE patterns with strains from human, bovine, porcine, caprine, and avian origin. Our results suggest the circulation of common Salmonella clones among several unrelated species and highlight that horses may act as potential reservoirs within a One Health framework. The identification of S. Freetown in equines, representing the first report in South America, further emphasizes the need to enhance the surveillance of the pathogen. Despite limitations due to sample size and underdiagnosis in veterinary settings, these findings support the inclusion of equine populations in epidemiological monitoring to improve the management of zoonotic risks associated with Salmonella.