Page 104 - June 2021

EQUINE HEALTH
SIGNS OF THE DISEASE
Equine coronavirus has a short incubation period, between 48 and 72 hours. Clinical signs generally persist for up to one week and horses can shed the virus in their feces for up to 21 days. Some infected horses remain subclini- cal, showing no clinical signs.
The typical signs of this viral infection include fever (which may go up to 105° F), lack of appetite, dull and depressed, possible colic, spending more time lying down than normal, diarrhea (may or may not present) and low white blood cell count.
In rare cases, there may be complications that include excessive protein loss and dehydra- tion, or neurologic signs (lethargy, depression, loss of body control) secondary to excessive ammonia in the body. These horses may become recumbent (unable to stand), followed by death.
In most cases, however, the disease is self-lim- iting; the horses recover in two to four days with treatment including anti-inflammatory medica- tion and fluids via nasogastric tube or intrave- nously if they haven’t been eating or drinking. Only a few horses become seriously ill. About 10 to 15% develop gastrointestinal signs, mainly colic but also changes in fecal consistency—everything from cow-pie appearance to watery diarrhea—but most of these horses generally recover.
Equine coronavirus infections result in high morbidity (many affected) and low mortality (only a few will die). Horses generally recover from the infection within 3 to 7 days, but some develop complications and deterioration that warrant euthanasia.
Approximately 7% of horses that become ill with coronavirus develop fatal complications such as shock and multiple organ failure. Some show neurological impairment, including circling, head pressing and recumbency. One theory regarding these fatalities is that the virus in some cases can cause such severe damage in the small intestine that the intestinal wall leaks bacteria and waste products into the bloodstream. This can cause septicemia (systemic infection), and waste prod- ucts such as ammonia can build up in the blood and eventually reach the central nervous system.
Horses with sudden onset of fever, lethargy, and anorexia, but no respiratory signs, should be tested for ECoV—submitting respiratory and fecal samples to a diagnostic lab.
TRANSMISSION
The virus is highly contagious, spread
by fecal-oral transmission when feces from an infected horse are ingested by another horse or when feed or water is contaminated by feces from the sick horse. The virus can also be transmitted when horses make oral contact with surfaces or objects contami- nated with infected feces. Stalls, muck forks, manure spreaders, thermometers and cloth- ing are common fomites (objects or materials that can harbor the virus). ECoV is most diagnosed in winter. There is no evidence that it can be transmitted to humans or other animals, but appropriate biosecurity measures should be practiced with all horses that have diarrhea or when horses are show- ing clinical signs consistent with ECoV.
Fecal viral shedding begins 3-4 days after exposure. Peak shedding occurs 3-4 days after development of clinical signs. This timeline may result in some horses testing negative to fecal PCR tests during the very early stages of clinical disease.
Clinical signs generally resolve within
a few days to a week with supportive care. Outbreaks typically last about 3 weeks. Fecal viral shedding has been shown to range from 3-25 days, however some cases have been documented to shed at 99 days, and intermittent shedding may occur. Asymptomatic shedders (with no signs of illness) do exist and may play a role in the spread of disease. These horses do not show clinical signs but are still shedding the organism in their manure.
At this point we don’t know how long the virus can survive in the environment. Human coronaviruses have been shown to survive longest at cool temperatures (about 39 degrees F)—and may live up to 14 days in waste water and 17 days in feces—but we don’t know if the equine coronavirus is similar in duration.
We also don’t know how long a horse might be a carrier, shedding the virus, after recovery, but the virus can be present in samples for 3-15 days afterward, and horses with no clinical signs have been found to shed the virus.
The virus is highly contagious, spread by fecal-oral transmission when feces from an infected horse are ingested by another horse or when feed or water is contaminated by feces from the sick horse.
DIAGNOSIS
Equine coronavirus is diagnosed based on the clinical signs, bloodwork—low white blood cell count—and the exclusion of other causes. Infection is confirmed
by detection of the virus in fecal samples, usually by quantitative PCR test. Other diagnostic techniques such as immunohisto- chemistry, electron microscopy, and antigen capture ELISA may be used, but are less sensitive than PCR.
Equine coronavirus in adult horses older than 2 years of age is generally seen as a single infection. When seen in foals, it is usually a co-infection with Rotavirus or Clostridium perfringens. The disease is most common during the cold weather months from October through April, but cases have also been diag- nosed in the summer.
IS THIS DISEASE BECOMING MORE PREVALENT?
The Cornell University Animal Health Diagnostic Center (AHDC) has seen a rise in diagnosis of equine enteric (intestinal) coronavirus cases since initial outbreaks were investigated in 2010. The AHDC Veterinary Support Services veterinarians are attributing this increase in this area of the Northeast to increased awareness of the disease and more diagnostic submissions. Since 2013, more than 2,000 samples have been submit- ted to the AHDC for equine coronavirus testing, of which approximately 18% have tested positive.
The virus has been isolated from several outbreaks across the United States, Europe, and Japan. Seroprevalence (number of animals that have evidence of equine corona- virus in their blood) in the U.S has been estimated at 9.3% even though many of these animals are not sick.
About 10 to 15% of those infected develop gastrointestinal signs, mainly colic but also changes in fecal consistency.
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