Salmonella in horses at slaughter and public health effects in Italy.

Overview

• This study investigated the presence of Salmonella enterica in horses and other equids at slaughter in Northern Italy and assessed the potential public health risk linked to consumption of raw horse meat.
• The research combined microbiological testing of equid samples with genomic analysis and epidemiological data to explore any connections between Salmonella strains found in horses and human salmonellosis cases in the region.

Study Background and Objectives

• Salmonella enterica is a significant foodborne pathogen, and identifying animal carriers is important for controlling human infections.
• Horses and other equids are not common sources of salmonellosis, but raw horse meat consumption in some Italian regions raises potential risks.
• The study aimed to:
• Determine the prevalence of Salmonella in caecal contents and carcasses of equids at slaughter.
• Assess antimicrobial resistance profiles of any Salmonella strains found.
• Evaluate links between Salmonella isolated from equids and human salmonellosis cases through genomic comparisons.

Methods

• Sampling Period and Location: June to November 2021 in Emilia-Romagna, Northern Italy.
• Sampled Animals: 152 equids, including 146 horses, 5 donkeys, and 1 mule.
• Testing:
• Caecal contents collected at slaughter were tested for Salmonella presence.
• Carcass swabs were taken to assess contamination during slaughtering.
• Salmonella isolates underwent antimicrobial resistance testing against 15 drugs.
• Genomic Comparison:
• Whole genome sequencing and core genome multi-locus sequence typing (cgMLST) were used to compare Salmonella strains from equids and human patients reported in the regional surveillance system.

Key Findings

• Salmonella prevalence in caecal contents was low: 3 out of 152 (2.0%).
• No Salmonella contamination was detected on the carcass surfaces after slaughter.
• Identified Salmonella serovars included Enteritidis, Typhimurium, and Stanleyville.
• Only one isolate, S. Typhimurium, exhibited antimicrobial resistance with a profile including ampicillin, chloramphenicol, streptomycin, trimethoprim, and tetracycline (AmCStxT).
• Genomic analysis revealed a direct match between S. Enteritidis from one horse caecal content and an outbreak strain affecting 17 human cases during the study period.
• Epidemiological investigation linked these human salmonellosis cases to consumption of raw horse meat products (“pesto di cavallo” and “sfilacci di cavallo”) sourced from batches originating at the studied slaughterhouse.

Public Health Implications

• The study demonstrates that even with low prevalence in equids and no detected carcass contamination post-slaughter, Salmonella in horse meat can cause human outbreaks.
• Raw horse meat products, popular in some Italian regions, represent a potential foodborne risk due to Salmonella carriage.
• A genomic match linking equid isolates to human cases underscores the need for integrated surveillance combining animal and human data.

Recommendations for Slaughter Practices and Consumer Safety

• Maintaining strict hygiene protocols throughout slaughter is critical, including:
• Proper hygiene at animal lairage (holding areas before slaughter).
• Careful slaughtering and carcass dressing procedures to prevent cross-contamination.
• Continuous monitoring and testing of equids at slaughter to detect Salmonella presence and antibiotic resistance.
• Public health messaging may be necessary to inform consumers about risks associated with raw horse meat consumption.

Conclusions

• This study highlights horses as potential reservoirs for Salmonella enterica that can lead to human infections, particularly linked to traditional raw horse meat products.
• It stresses the importance of combining microbiological testing, antimicrobial resistance screening, and genomic epidemiology to understand and mitigate zoonotic risks.
• Enforcing hygiene in slaughterhouses and awareness among consumers remain key strategies to reduce salmonellosis risks from horse meat.