Page 103 - June 2021

EQUINE HEALTH
“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. ”
illnesses isolated a pathogen from the manure of the affected horses and found it was equine coronavirus (ECoV), an organism previously associated with illness in foals.
Two years later, Dr. Ron Vin, an equine veterinarian in New Hampshire who was doing consulting with IDEXX laboratories, began receiving a few calls about horses
with fever and diarrhea. These were sporadic cases and at first he thought they were incidental findings. Then two veterinarians from Washington State—Dr. Anne Marie Ray and Dr. Alice Lombard—asked his advice regarding a small outbreak of illness in horses they were treating that had colic, diarrhea and fever.
About the same time, Dr. Nicola Pusterla, a researcher at UC-Davis, was seeing similar cases and receiving reports of outbreaks in adult horses—mainly on large farms, show barns and boarding facilities. Pusterla later wrote a report stating that these horses had nonspecific signs - fever, depression, going off feed - and it was difficult to pinpoint which body systems were being affected because there was no nasal discharge, no cough or diarrhea. Bloodwork showed only a drop in white blood cells, which is common in viral illnesses. A few of the horses had mild colic or soft manure.
Pusterla began testing the horses for com- mon viruses, such as equine herpesvirus-1 and influenza, but those tests came back nega- tive. During a later outbreak, he asked the attending veterinarians to send every sample they could—including blood, nasal secretions, feces, and urine—and he tested for every organism for which there was a test. The only equine pathogen that was detected in all of those horses was coronavirus.
In New Hampshire, Vin also found that the horses with similar pathology and blood changes that he was asked to check were all positive for ECoV. From November 2011 through April 2012 these two researchers worked with 161 cases in four outbreaks on farms in California, Texas, Wisconsin, and Massachusetts. Several of the sick horses died or were euthanatized due to complications.
FIRST SEEN IN FOALS
In earlier years ECoV, had been considered
a disease of foals, but not adult horses. The first case study of illness linked solely to a coronavi- rus was published in 2000 after a Quarter Horse filly developed severe diarrhea at two days of age, and her fecal samples were negative for all other known intestinal pathogens. That foal became sicker, with multiple complications. With no hope for survival, she was euthanatized. At necropsy, evidence of coronavirus infection was found in her intestinal wall, and the virus was identified via cross-reactivity using the closely-related bovine coronavirus (BVC).
Later that year, a coronavirus was identified in the feces of a 2-week-old Arabian foal that was sick with fever and diarrhea. The virus was analyzed genetically and found to be 90% simi- lar to BCV but different enough to be consid- ered a separate species. The researchers named it equine coronavirus ECoV, strain NC99. That foal recovered after 6 days of supportive care.
Other cases were subsequently seen in foals, but the virus was never recognized in adult horses until several years later, and researchers weren’t even sure about the role it played in foal diarrhea. In a 2010 survey in Kentucky, ECoV was found in feces of 29% of foals with diarrhea, but the virus was also found in 27% of healthy foals. This made people wonder if equine coronavirus is a true pathogen or just sometimes happens to be present in both sick and healthy animals.
RESEARCH INTENSIFIED
Research on ECoV continued after the first cases in foals and intensified after outbreaks occurred among adult horses. Pusterla and colleagues tested manure samples from 96 healthy horses and 44 sick horses in barns where outbreaks occurred and found that 86% (38
out of 44) of the sick horses tested positive for the virus, while 93% of the healthy ones (89 out of 96) tested negative. Thus the likelihood of finding ECoV in the horses with clinical signs of illness was 91% and the researchers determined there was probably some correlation.
In the years since those first 4 outbreaks were described in Pusterla’s paper, there have been other outbreaks in the U.S. and some in
Europe. Another outbreak at the racetrack in Japan involved a strain (ECoV-Tokachi09) that is different from the one found in the U.S.
Some coronaviruses spread throughout
the body and cause systemic illness, but other strains tend to attack specific areas or organs. For instance, some strains only affect the epithelial cells lining the respiratory tract or the intesti-
nal wall, creating localized infections. In the intestine, these viruses damage the villi, the tiny fingerlike projections of the intestinal lining that facilitate fluid and nutrient absorption. The result of this damage is inability to absorb the fluid and nutrients passing through, and diarrhea.
In earlier years, ECoV had been considered a disease of foals, but not adult horses. The virus was never recognized in adult horses until several years later.
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