Wild horses and horse manure as reservoirs for Clostridiodes difficile in Australia

Abstract

Background: Clostridiodes (Clostridium) difficile poses an ongoing threat as a cause of diarrhoea in both human and animal populations. Recent emergence of human disease caused by strains of C. difficile found in animals adds to mounting evidence that C. difficile infection (CDI) is a zoonosis. In Australia, horses represent a unique mix of companion and wild animals. While C. difficile is regularly isolated from domesticated horses, little is known about C. difficile in wild horses, known as brumbies in Australia. The aim of this study was to investigate the prevalence and characteristics of C. difficile in wild horse populations, and in publicly available horse manure to evaluate its potential as a source of C. difficile in the community. Methods and materials: One hundred and twenty-six wild horse faecal samples were collected from Western and South-Eastern Australia and 60 publicly available horse manure samples were collected from Western Australian metropolitan areas. Samples were cultured in enrichment broth followed by alcohol shock and subsequent plating onto differential agar. C. difficile isolates were characterised by ribotyping using capillary electrophoresis, and toxin profiling by PCR. Results: The overall C. difficile prevalence was 15.1% in wild horses and 31.7% in publicly available horse manure, a statistically significant difference (P=0.048). Thirty-one ribotypes (RTs) were identified across all samples; the most prevalent were RTs 010 (a non-toxigenic strain), 054, 056 and 015. These RTs have been previously isolated from vegetables, livestock and humans in WA. Two additional noteworthy isolates included an esculin hydrolysis negative strain and a non-toxigenic RT078 strain. Conclusion: This study is the first known investigation into C. difficile in wild horse populations and the first to look specifically at C. difficile in horse manure available for public use. Prevalence of C. difficile was higher than previously reported in horses, and some unusual strains that require further investigation were isolated. The study provides preliminary information on the epidemiology of C. difficile in wild horses and support the hypothesis that horse manure represents a potential reservoir of C. difficile in the community.