Infection of adult horses with Equine Coronavirus (ECoV) is now being reported worldwide with an increasing incidence. This is primarily due to recognition of the clinical syndrome and the availability of good diagnostic testing. Disease may occur in individual horses or less commonly in groups of animals. The virus has also been linked to diarrhoea in foals. ECoV infection of adults, although more widely recognized, is still relatively uncommon. A serological survey in the US reported that 10% of adult horses had antibodies, reflecting exposure to the virus. The prevalence of ECoV in Australian horses is unknown, although infection and disease certainly occurs.
Equine coronavirus (ECoV) and the human COVID-19 are two very distinctively different viruses. Generally, most coronaviruses are species specific and there is zero evidence that ECoV causes infection or harm in humans. There has been recent evidence that human SARS-CoV-2 can cause infection, based on seroconversion, without disease in an adult horse (see article in the journal Viruses).
Signs
The time from infection to signs is typically 2 – 4 days. Exposure can occur directly from horse to horse (from both unaffected carriers and clinically sick horses), or via fomites. Most cases are relatively mild and can occur all year, although may be more common in colder months. Miniature horses may be at a greater risk of moderate to severe complications of ECoV. The most common presenting signs are lethargy and fever. Horses typically refuse feed and may show signs of mild colic. Faecal output is reduced, and diarrhoea is an inconsistent finding.
Routine bloodwork often reveals a low total white blood cell count (leukopaenia) with both low numbers of neutrophils (neutropaenia) and/or lymphocytes (lymphopaenia).
In a small number of affected horses (especially Miniatures) there may be low total blood protein concentration (hypoproteinaemia), and disturbed electrolyte and metabolic parameters (e.g., elevated blood lactate) due to intestinal damage. Some will have elevated blood levels of ammonia with neurologic signs, including obtundation, aimless wandering, circling, ataxia and seizures.
Diagnosis
The most important aspect is that the veterinarian is aware of the clinical syndrome and diagnostic methods available. Although it has been recognized for more than 10 years it may not be considered by many veterinarians, particularly in regions where the prevalence is not known. The disease diagnosis is based on a positive test on faeces or small intestinal contents. The test involves molecular detection via a PCR test. In an outbreak it is useful to test asymptomatic in-contact animals in order to identify and confine shedders.
Faecal shedding of the virus varies between 3 and 25 days after infection. To date no known carrier or reservoir stage has been identified, but this remains a possibility.
Treatment
Most cases are relatively mild and require little support, although non-steroidal anti-inflammatory drugs, such as flunixin meglumine, may be helpful. More severe cases require fluid therapy, and potentially colloid support if the protein levels are falling rapidly. Cases should be isolated from others, and there should be strict manure handling and biosecurity in place to prevent transmission. Ideally positive animals should remain isolated until they become PCR test negative in their faeces.
Prognosis and prevention
Generally, the prognosis is very good. There is no vaccine available.
Tags: Gastrointestinal diseases; Infectious diseases