Other Names
- EVE
- Equine Rotavirus Enteritis
- Viral Gastroenteritis in Horses
- Foal Diarrhoea (viral)
What is Equine Viral Enteritis?
Equine Viral Enteritis (EVE) is an infectious gastrointestinal disease caused by viral pathogens that inflame and damage the lining of the small and large intestines. The disease most commonly affects foals, though adult horses can also be infected. In foals, it is a leading cause of neonatal diarrhoea and, if severe, can result in life-threatening dehydration and electrolyte imbalance within a matter of hours.
The term EVE encompasses infections from several different viruses, with equine rotavirus being the most clinically significant and widespread cause. Other viral agents associated with equine enteritis include equine coronavirus, equine adenovirus, and equine parvovirus-hepatitis. Understanding which virus is responsible is important both for treatment and biosecurity management, as some agents spread rapidly through yards and breeding establishments.
Causes
The primary viral causes of equine enteritis include:
- Equine Rotavirus: The most common cause of viral enteritis in foals under three months of age. Highly contagious and environmentally stable — the virus can survive for months in faecal material and on surfaces. Spread via the faecal-oral route.
- Equine Coronavirus: More typically associated with enteritis in adult horses, though foals can also be affected. Outbreaks have been reported in groups of adult horses, often following stress or transport.
- Equine Adenovirus: Generally a respiratory pathogen but occasionally implicated in intestinal disease, particularly in immunocompromised animals.
- Equine Parvovirus-Hepatitis (EqPV-H): Primarily hepatotropic but associated with some gastrointestinal signs.
Transmission is predominantly faecal-oral, through direct contact with infected horses, contaminated bedding, feed, water, or equipment. In breeding facilities, the virus can spread rapidly between mares, foals, and handlers.
Symptoms and Signs
Signs vary by age of the horse and the causative virus. In foals, onset can be sudden and deterioration rapid:
- Profuse watery or liquid diarrhoea — often yellow or pale in colour
- Lethargy and depression
- Reduced or absent interest in nursing
- Dehydration — assessed by skin tent test, sunken eyes, dry mucous membranes
- Abdominal discomfort or pain
- Fever, particularly in the early stages
- Weight loss if the disease is prolonged
In adult horses with coronavirus, signs may include lethargy, anorexia, mild colic, and soft to liquid faeces. Adult horses rarely develop the severe dehydration seen in foals, but secondary complications including colitis and bacterial translocation can occur.
Dehydration is the principal danger in foal cases. A foal that is too weak to stand or has lost more than 8–10% of its body weight in fluid is in critical condition and requires immediate veterinary intervention.
Diagnosis
Clinical signs are suggestive but not diagnostic, as bacterial and parasitic causes of diarrhoea must be ruled out. Diagnostic steps include:
- Faecal virus detection: ELISA (enzyme-linked immunosorbent assay) is commonly used to detect rotavirus antigen in faeces. Results are rapid and reliable in the acute phase of infection.
- PCR testing: Polymerase chain reaction allows detection and identification of multiple viral agents simultaneously, including coronavirus and less common pathogens.
- Electron microscopy: Can visualise viral particles directly from faecal samples but is less widely available.
- Blood work: Haematology and biochemistry to assess hydration status, acid-base balance, and electrolyte levels, guiding fluid therapy requirements.
- Faecal culture: To rule out concurrent bacterial causes such as Salmonella, Clostridium, or Campylobacter.
Treatment
There is no specific antiviral treatment for equine viral enteritis. Management focuses on supportive care to maintain hydration and electrolyte balance while the immune system clears the infection:
- Fluid therapy: Oral electrolyte solutions for mildly affected foals; intravenous fluids for moderate to severely dehydrated animals. Balanced polyionic solutions are the standard of care.
- Nutritional support: Encourage continued nursing where possible. Parenteral nutrition may be required in foals unable to tolerate enteral feeding.
- Probiotics and gut protectants: Products containing Lactobacillus or bismuth subsalicylate may help support gut recovery, though evidence in horses is limited.
- Anti-ulcer medication: Omeprazole is often administered to foals to prevent stress gastric ulceration during illness.
- Antibiotics: Not indicated for viral enteritis itself but may be prescribed if secondary bacterial infection or bacteraemia is suspected.
- Biosecurity measures: Isolation of affected animals is essential to prevent spread. Thorough disinfection of stabling, equipment, and handler clothing.
Prevention
Prevention is particularly important on breeding farms where rotavirus outbreaks can sweep through a foal crop:
- A rotavirus vaccine is available for use in pregnant mares — vaccinating mares at 8, 9, and 10 months of gestation helps ensure foals receive protective antibodies via colostrum
- Ensure foals ingest adequate high-quality colostrum within the first two hours of birth
- Isolate new horses before introducing them to an existing herd
- Maintain strict hygiene protocols — particularly hand washing and equipment disinfection between foals
- Disinfect foaling boxes thoroughly between use; rotavirus resists many common disinfectants, so use agents specifically active against non-enveloped viruses
Prognosis
Most foals with viral enteritis recover fully with prompt supportive care. The prognosis is closely tied to the severity of dehydration and how quickly treatment begins. Foals that receive adequate fluid therapy within the first 12–24 hours of illness generally do well. Cases involving concurrent bacterial infection, failure of passive transfer, or severe metabolic acidosis carry a more guarded prognosis. Adult horses with coronavirus enteritis typically recover within 3–7 days with supportive management.
When to Call the Vet
Call your vet immediately if:
- A foal develops diarrhoea — any diarrhoea in a young foal warrants prompt veterinary assessment
- The foal appears weak, lethargic, or unwilling to nurse
- Diarrhoea is profuse or blood-tinged
- You suspect rapid deterioration or dehydration
- Multiple horses or foals in a group develop gastrointestinal signs simultaneously
Early fluid therapy can be the difference between full recovery and a fatality in young foals. Never adopt a wait-and-see approach with neonatal diarrhoea.
Frequently Asked Questions
Is equine rotavirus contagious to humans?
Equine rotavirus is not considered a significant zoonotic risk, but basic hygiene precautions — thorough hand washing after handling affected animals — are always advised. Immunocompromised individuals should take extra care and consult a health professional if concerned.
How long does a foal with EVE shed the virus?
Foals infected with rotavirus typically shed virus in their faeces for 7–10 days, though shedding can persist for up to two to three weeks in some cases. Strict isolation and hygiene should be maintained throughout the shedding period.
Can adult horses get equine viral enteritis?
Yes. Equine coronavirus in particular causes outbreaks in adult horses. While most adult horses develop milder disease than foals, some can become seriously ill. Horses under stress — recently transported, stabled in high density, or immunosuppressed — are at greatest risk.
Does the rotavirus vaccine fully protect foals?
Vaccinating mares reduces the severity and incidence of rotavirus diarrhoea in foals but does not guarantee complete protection. The vaccine works by boosting maternal antibody levels in colostrum; adequate colostrum intake by the foal is therefore essential for the vaccine programme to be effective. See also: Equine Foal Immunodeficiency Syndrome for more on foal immune vulnerabilities and colostrum for its role in neonatal immunity.