The Unseen Enemy: Equine Coronavirus and Your Horse’s Health

What is Equine Coronavirus?

A variety of species suffer from the coronavirus. The virus tends to affect specific organ systems in the affected species, and the equine coronavirus affects the gastrointestinal tract. The coronavirus that affects humans has an affiliation with the respiratory tract. 

The coronavirus in horses is unlikely to be infectious to humans. Still, all people that come into direct contact with a sick horse should observe strict biosecurity protocols as this virus family carries zoonotic risk factors.

Horse foal in the grass

How Can Horses Get COVID?

Through the years, many people considered horse COVID a disease that mainly affected foals, but recent studies show that horses of all ages are susceptible to the disease.   

Equine COVID (ECoV) spreads when an infected horse’s feces contaminate the environment. 

The environmental contamination of feed sources results in the virus’s fecal-oral transmission to horses grazing in infected pastures. 

The virus also survives on tools or surfaces in the stables or yard that come into contact with feces. Grooms that muck stables with the exact mechanisms may spread the virus on the tools they use or their clothing. Another significant contamination source includes rectal thermometers used on multiple horses without being sterilized between use.

Vets refer to these objects or contact staff as fomites as they act as carriers of the disease, resulting in the rapid spread of a virus if not caught early. 

The prevalence of ECoV appears mainly in the late autumn or winter months. 

The Disease Incubation Period

The incubation period of a disease is the time that elapses between the horse’s initial exposure to the virus and the manifestation of clinical symptoms. 

The incubation period is short as signs of horse COVID start two to four days after a horse’s exposure to the virus. The clinical symptoms are sometimes missed by staff as the gastrointestinal symptoms are mild and generally self-limiting. 

The Duration of the Disease

The disease’s clinical symptoms begin 48 to 72 hours after infection, with a high morbidity and low mortality index. 

Also, the disease has several stages, and the timeline of these stages affects the outcome of test results if a vet tests a horse too early. Listed below are the stages of ECoV:

  • Infection and incubation: The virus survives in an environment with low temperatures. ECoV persists for fourteen days in wastewater and seventeen days in feces. The horse comes into contact with the virus and then incubates in the GI tract for two to four days.
  • Clinical symptoms: The disease produces overt symptoms for a few days, but generally, they fully recover with supportive care after one week. An outbreak in a yard typically lasts around three weeks. 
  • Shedding: Viral shedding peaks three to four days after the initial onset of clinical symptoms. The test may yield a false negative if a vet collects a sample from a horse for a fecal PCR before this shedding period. Horses can shed the virus for three to fifteen days after infection. 
  • Carrier status: Horses can shed the virus for three to twenty-five days, but some records documented horses shedding the virus for ninety-nine days. 

Clinical Signs and Bloodwork Abnormalities

The primary clinical signs of equine coronavirus include a fever ranging between 101.5°F – 106°F (38.6°C – 41°C), depressed appetite, and decreased activity levels. A fifth of ECoV cases show gastrointestinal symptoms like diarrhea or colic

Secondary complications may arise, which include shock, organ compromise, or neurological abnormalities. The morbidity of the equine coronavirus is high, but the mortality is low. Horses that develop complications that do not respond to treatment may deteriorate or require euthanasia. 

Signs that owners can look out for that indicate ECoV include:

  • Fever.
  • Soft stools or profuse diarrhea.
  • Colic symptoms like flank checking, kicking at their abdomen, or attempts at rolling. 

The blood tests vets run may not show any changes, but some cases report decreased white blood cell counts due to decreased neutrophils and lymphocytes. The red blood cell profile remains unremarkable, but hypoalbuminemia can occur secondary to diarrhea. 

Increased ammonia concentrations in the bloodstream occur when urease-producing bacteria overproliferate in the GI tract or the gut leaks ammonia due to a disrupted mucosal barrier. Hyperammonemia may lead to neurological abnormalities such as uncoordinated movements, depressed mentation, increased periods of lying down, or an inability to stand up. 

Death due to equine coronavirus does not occur frequently, but if the secondary complications become severe, the risk of death increases, especially if a horse becomes recumbent.

Clinicians treating any horse presenting with an acute fever, lethargy, depressed appetite, and no signs of a respiratory infection must consider testing the patient for ECoV. Labs recommend submitting both fecal and respiratory samples to the diagnostic laboratory.

Horse owner and vet with horse

What are the Steps to Diagnose Equine COVID

A veterinarian needs to look at the complete clinical picture of a horse with fever, anorexia, and diarrhea without respiratory signs to consider an ECoV infection. A medical history does not prove helpful as there are no predisposing factors to Corona infections besides recorded contact with an infected horse. 

The vet must exclude several other common causes of diarrhea to determine if testing for ECoV is warranted. The clinical presentation and abnormal blood work provide the vet with some clues and help to decide what samples and diagnostic tests to order. 

Equine coronavirus diagnosis confirmation requires a quantitative Polymerase chain reaction (qPCR) test. The other test options include immunohistochemistry, electron microscopy, and antigen capture ELISA, but the sensitivity of these tests is less than the qPCR tests.

Samples required for submission include fresh feces stored in an unbreakable leak-proof container. Diagnostic labs recommend keeping samples on ice, and they must reach the lab within 24 hours, preferably via an overnight courier. If the specimens take too long or become too warm, commensal bacteria may overgrow and cause PCR test inhibition. 

Samples that cannot reach the lab within 24 hours or that may experience delays by three to four days should be frozen to avoid bacterial overgrowth. Submitting a fresh, unfrozen specimen is crucial as parasitology tests require fresh feces for accurate analysis. The PCR test for Equine Enteric Corona takes three business days for the lab to complete.

Clinicians may perform transabdominal ultrasounds to support the colitis diagnosis often found with ECoV infections. 

How is ECoV treated? 

There is currently no medication to treat ECoV, such as antiviral drugs, so clinicians only use supportive treatment to combat the secondary complication of the virus. The disease infects most horses that come into contact with the virus, but the death rate is low if no significant complications occur. Most horses recover spontaneously without any treatment. 

Supportive treatment for horses showing more significant clinical symptoms may include nonsteroidal anti-inflammatory drugs (NSAIDs). Most available NSAIDs, such as flunixin meglumine or phenylbutazone, require a prescription from the attending veterinarian. 

Horses with severe colic symptoms or profuse diarrhea may require additional fluid therapy, electrolyte supplementation, or gastrointestinal protectants, such as Omeprazole or sucralfate.

Which Control Measures Should be in Place?

Equine coronavirus does not have a licensed vaccination, so the only means to protect horses from the virus is strict adherence to biosecurity protocols, especially during outbreaks. 

Biosecurity practices must focus on proper hygiene practices, stable management, close daily monitoring of all horses for signs of illness, isolating sick horses, and avoiding muzzle-to-muzzle contact between horses. 

ECoV has a short environmental survival time and remains viable in optimal conditions for two to three days. Most commercially available disinfectants for routine stable cleaning protocols kill the​​ virus quickly. 

Good practices to maintain high hygiene standards include regular stable sanitization and communal facilities and equipment. The correct disposal of manure is paramount when dealing with viruses that spread through feces. 

Areas that have high traffic and are often soiled by horses should always first have the manure removed, and then the staff should disinfect the area. 

Biosecurity measures must include regulations that isolate all horses with a fever and no evidence of respiratory illness. The combination of diarrhea and the symptoms mentioned above indicate concern for ECoV, and staff must handle the affected horse last during grooming, cleaning, and feeding schedules. 

Any horse moved from a facility or stable with ECoV cases must undergo quarantine for three weeks before inception into the new yard’s routine. 

Footbaths, disposable gloves, and individual thermometers for each horse also reduce the virus’s spread and are reasonable biosecurity measures. 

Cleaning products effective against the virus must lead to its inactivation. Some of the products that kill the virus include:

  • Bleach.
  • Povidone Iodine.
  • Quaternary Ammonia products.
  • Chlorhexidine gluconate.
  • Phenols containing compounds. 

Organic debris decreases the efficiency of cleaning products, so staff must first remove manure and bedding materials before they apply cleaning products to achieve maximum efficiency. 

Staff should regularly wash their hands between horses or individual stables when performing daily tasks such as grooming, feeding, mucking stables, or handling horses. Healthy horses with robust immune systems are less likely to contract viruses, so routine annual vet visits, deworming schedules, and vaccinations help to keep horses in tip-top shape. 

The Prognosis of COVID in Horses

The morbidity of equine coronavirus ranges between 10 and 83 percent, so many horses exposed to the virus will become ill, but very few will die. Most horses fully recover, so the prognosis is good unless the horse develops severe secondary complications. 

The prognosis becomes poor when the complications of the virus compromise the mucosa of the large intestine. Complications that lead to leaky guts may result in septicemia, endotoxemia, or hyperammonemia-associated encephalopathy. 

Other Facts About the Disease

Some owners may wonder, “can a horse test positive for COVID-19?” The virus strain that affects horses differs significantly from the COVID-19 that infects humans. Currently, no evidence exists that indicates that horses or any domestic animals can infect humans with COVID-19. 

The coronaviruses fall into a big group of RNA viruses that have three serotypes, alpha, beta, and gamma coronaviruses. ECoV is a beta coronavirus that causes disease outbreaks across the globe. Increased awareness of the disease is due to increased testing in horses with fever, diarrhea, and no respiratory symptoms. 

According to recent studies, the seroprevalence of equine Coronavirus is around nine percent. The virus identification has steadily increased since 2010 as it became more prevalent in the USA. 

The age demographic for ECoV includes adult horses over the age of two years. Foals diagnosed with ECoV sometimes have concomitant infections of Rotavirus or Clostridium perfringens, rapidly increasing the risk of serious complications.

The virus occurs mainly in the colder seasons, from October to April, but some cases have occurred in the summer months, so researchers are yet to establish a distinct seasonality. The Northeast of America seems to have most of the reported cases, which researchers consider to be due to the increased awareness of ECoV.

The coronaviruses that cause respiratory diseases in humans include Severe Acute Respiratory Syndrome (SARS), Middle East Respiratory Syndrome (MERS), and the infamous COVID-19. None of these viruses affect horses, so they cannot be transmitted between humans and horses, even though they are coronaviruses. 

Other animals affected by coronaviruses include pigs suffering from Transmissible Gastroenteritis (TGE), Porcine Epidemic Diarrhea (PED), and cats developing Feline Infectious Peritonitis. 

The coronavirus got its name from the spikes on the virus’s surface, which look like a crown. The virus has an envelope that surrounds it with a membrane. The membrane is permeable, and this property makes the virus susceptible to disinfectants and less stable in the environment. Non-enveloped viruses are tougher to kill and survive longer outside of a host, 

The World Organisation for Animal Health (OIE) website does not list ECoV as a notifiable disease.


The End

The development of gastrointestinal signs in horses with fevers is sometimes inconsistent, and vets do not always suspect a virus. An important key point for horse owners and vets to consider is that ECoV should feature at the top of their list if a horse has a fever, no respiratory symptoms, and diarrhea. 

If equine coronavirus gets suspected, vets must submit fecal samples, not nasal swabs, to ensure the lab performs the proper molecular diagnostic workup.

The horses affected by ECoV may show no symptoms or very subtle symptoms. They also shed the virus for two to five weeks, meaning that outbreaks occur suddenly and may last for extended periods unless vets get the correct diagnosis.  

The sooner the vets identify ECoV, the sooner management can implement biosecurity protocols and quarantine measures to curb the spread of the virus. 

The coronavirus is highly contagious in horses and high-risk environments such as breeding facilities, working farms or ranches, boarding facilities, and densely populated stable yards. Good hygiene practices, annual primary health care, and stringent biosecurity measures decrease the risk of infection in environments with large groups of horses.