Science-in-brief: Equine coronavirus – a decade long journey to investigate an emerging enteric virus of adult horses.

The research article reviews studies conducted over a decade on Equine coronavirus (ECoV), a virus increasingly seen in adult horses. The authors discuss the virus’s classification, how is it transmitted, the symptoms it causes in horses, and diagnostic techniques to identify infections.

Understanding the Equine Coronavirus

• ECoV belongs to the Coronaviridae family along with viruses like human coronaviruses OC43, 4408, and HKU1, and bovine, porcine, canine, mouse, bubaline, and rat coronaviruses. It’s part of the Betacoronavirus 1 genus but is genetically distinct from SARS-CoV-2 affecting humans. There is no evidence showing that the virus can be transmitted from horses to other animals or humans.

ECoV Under the Microscope

• Research in this area started about 11 years ago when a group of scientists investigated an outbreak of fever and intestinal symptoms among young racing horses in Japan. Only about 10% of the affected horses showed digestive symptoms. Similar outbreaks resurfaced three years later.
• Studies over the years have provided greater clarity on the signs of ECoV infection which has been perplexing due to the inconsistent development of digestive symptoms. Where diarrhoea is consistently associated with inflammation in foals, the same might not be true for adult horses.

Recovery and Morbidity Rates

• Most horses infected with ECoV generally recover in 2-4 days with minimal or no medical treatment, though some adults may need intensive care to treat leukopenia, systemic inflammation, and metabolic disturbances. Morbidity rates tend to range between 17% and 57%.
• Various factors play a role in the susceptibility to and outcome of ECoV infection. Observations suggest that the clinical expression of ECoV might be age-dependent, with foals rarely developing a clinical disease. A possible protection against infection might exist due to the virus circulating between foals and breeding stock, as seen from the higher seroprevalence in healthy breeding animals compared to non-breeding horses.

Diagnosing ECoV

• A lack of digestive signs can often incorrectly lead veterinarians to rule out an enteric pathogen. An observed consistent haematological abnormality is leukopenia, though it’s not a definitive indicator of ECoV.
• The laboratory support to confirm ECoV infection relies on detecting the virus in faeces. Quantitative real-time PCR (RT-qPCR) has replaced previous detection methods such as electron microscopy and antigen capture ELISAs. RT-qPCR enables detection of viral kinetics and helps determine the contagious nature and prognosis of the horse’s condition. Research has shown that ECoV RNA can be detected within 72-96 hours from inoculation until 10-14 days post-infection. In naturally infected horses, detection time can extend up to 25 days from the onset of clinical disease.
• Though research on ECoV is limited, it’s been seen that longer duration and higher peaks of viral shedding are observed in clinically versus non-clinically infected horses. Both populations show contrasting viral loads.