A study of Salmonella in horses in Italy has uncovered an outbreak that affected 17 people.

From June to November 2021, 146 horses, five donkeys, and one mule were tested for Salmonella in cecal contents and through carcass swabs from one slaughterhouse.

Salmonella was detected three times in 152 of the cecal contents, while all 152 carcass samples were negative. According to the study published in the International Journal of Food Microbiology, Salmonella Enteritidis, Typhimurium, and Stanleyville were identified.

Countries of horse origin were France, Italy, Poland, Hungary, Slovenia, and Germany. They were slaughtered twice a week but arrived at the slaughterhouse daily.

Outbreak identification
Salmonella was detected in June 2021 and late September 2021. Nine horses were tested in June, and two cecal samples were positive for Salmonella Enteritidis and Stanleyville. These animals came from Hungary and Italy. In September, seven were tested, and the positive one, from Italy, carried Salmonella Typhimurium.

Considering the consumption of ground horse meat called “pesto di cavallo” and dried and smoked strips named “sfilacci di cavallo” in Northern Italy, researchers investigated the link between horse meat and human salmonellosis in this area.

In July 2021, whole genome sequencing-based surveillance in Emilia-Romagna signaled a potential outbreak of Salmonella Enteritidis, including nine isolates across Piacenza, Parma, and Reggio-Emilia provinces. The first isolate came from May 2021, and the last came from August.

In June, a genomic match was found between the Salmonella Enteritidis isolated from horse cecal content and an outbreak of 17 cases in Emilia-Romagna.

Epidemiological investigations highlighted some cases of reported consumption of horse meat. They traced different batches of the meat, released weeks apart from each other, to the slaughter site in the study. Five of eight cases reported eating uncooked horse meat.

Horse meat associated with cases and traced to the slaughterhouse was produced in May and June 2021, while the horse carrying the outbreak strain of Salmonella Enteritidis was slaughtered weeks later, in June 2021. This means meat from that animal could not have infected those cases.

Environmental contamination
Scientists said the outbreak strain was likely already present in the slaughterhouse environment before the horse arrived from Hungary and that environmental persistence could have caused contamination. The environment could have been contaminated before June and have affected meat produced in early May. 

Supporting this is the finding that the last batch of horse meat associated with cases was from a horse from France and slaughtered two weeks before the Hungarian animal in June 2021. It appears unlikely that two horses from different countries slaughtered two weeks apart carried the same WGS type of Salmonella, said researchers.

An official visit to the slaughter plant found manure on the floor, dirty troughs, and pests in the lairage area. Improvement of hygiene measures at the lairage and along the slaughter line was demanded. The company also increased the number of carcasses routinely tested for surface contamination by Salmonella.

Scientists said despite findings showing a low prevalence, Salmonella in horse meat can represent a consumer risk.

“A key lesson from the study concerns the need to maintain a high level of hygiene during the entire slaughtering process. Hygiene at lairage is crucial to avoid cross-contamination between animals and the meat. For this reason, lairage conditions should be critically evaluated, and biosecurity measures must be properly implemented.”

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