Investigation of the infectious causes of diarrhoea in Australian thoroughbred foals

Abstract

Diarrhoea is a common disease in foals that is costly and labour intensive to manage. A large number of potential enteric pathogens have been detected in the faeces of foals, however, the role of these infectious agents in causing clinical disease is not clearly understood and their prevalence in Australia is unknown. In addition, timely methods for definitive diagnosis are not readily available for some of these agents. Therefore, this study aimed to develop rapid molecular detection assays to investigate the presence of equine rotaviruses, equine coronaviruses, Salmonella spp. and Clostridium difficile in Australian thoroughbred foals with and without diarrhoea.

A prospective case control study was conducted on five thoroughbred breeding farms in the Hunter Valley (New South Wales, Australia) during the 2010 breeding season. Faecal samples were collected from age-matched foals with diarrhoea and without diarrhoea from the same farm (age-matched pair). In addition, faeces were collected from foals with diarrhoea from an equine veterinary hospital. All faecal samples were analysed for equine rotaviruses, equine coronaviruses, Salmonella spp. and Clostridium difficile by quantitative PCR (qPCR) assay. All faecal samples were also cultured for Salmonella spp. using selective growth media. Samples positive by qPCR and 15 randomly selected control foal samples negative by qPCR were cultured anaerobically for Clostridium difficile.

Faecal samples were collected from 117 pairs of age-matched case control foals and 26 hospitalised foals with diarrhoea. In the age-matched case control foals, equine rotaviruses were the most frequently detected infectious agent (25% case foals, 5% control foals) and the only infectious agent significantly associated with the presence of diarrhoea. In hospitalised foals, Clostridium difficile (23%) was the most frequently detected infectious agent. In this investigation co-infections were detected in 4% of matched case foals and 4% of hospital foals, with equine rotaviruses and Salmonella spp. being the most frequent combination. Four different Clostridium difficile ribotypes were detected, including ribotype 012 and 078. Importantly, this is the first report of the detection of C. difficile ribotype 078 in Australian horses. As this ribotype has been associated with severe disease in humans, this finding may have public health implications. The availability of rapid molecular screening tests for infectious causes of foal diarrhoea enhances the veterinary practitioner’s ability to instigate appropriate therapy and control measures in foals with diarrhoea. However, the detection of pathogens in foals without diarrhoea highlights the need for more research into the role some of these pathogens play in clinical disease both individually and in combination.