Equine Rhinopneumonitis

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Also Known As

Foul nasal discharge, Herpesvirus-4, Rhino, Snots


Equine rhinopneumonitis has two sub-types: sub-type 1 causes abortions, respiratory and neurologic disease; sub-type 2 causes respiratory problems. The disease is highly infectious with transmission occurring by inhaling infected droplets or ingesting material contaminated by nasal discharges or through exposure to aborted disease-carrying fetuses.

Diagnosing equine viral rhinopneumonitis is difficult because symptoms cannot be differentiated from equine viral arteritis and equine influenza. Using clinical signs may be the first step in making a diagnosis, but it is necessary to confirm the disease through the use of virus isolation and serology testing in a laboratory.

The disease develops when the disease-carrying material attaches itself to cell receptors in the horse's respiratory system and enters the cell. New viral particles are released into the airway and infect other cells or become aerosolized resulting in protein-rich fluids pouring into the horse's airways. As this copious nasal discharge, often referred to as 'snots' by veterinarians and owners, accumulates, secondary bacterial infections may develop.

This excessive discharge or buildup of mucus in the throat and nose leads to congestion, fever, coughing, and mild to severe paralysis of the hind quarters. Mares may abort after three to twelve weeks of exposure, most commonly in the eighth to eleventh month of gestation. While a vaccine does not always prevent the disease, horses that have been vaccinated have less severe cases of the disease than horses that have not been vaccinated.


  • Listlessness and lack of appetite for food and water
  • Flu-like symptoms
  • Fever
  • Dry hacking cough
  • Nasal discharge
  • Swollen lymph nodes
  • Secondary bacterial infections
  • Weakness and paralysis of hind limbs
  • Abortion


The disease is caused by equine herpes virus Type 1 which has two sub-types: Sub-type 1 is the strain that causes abortions, respiratory and neurological disease. Sub-type 2 is a respiratory strain.


Proper vaccinations are the most important prevention in dealing with this disease. Effective vaccines are available and horses should be vaccinated several times a year to ensure immunity. A veterinarian should be consulted to develop the best vaccination protocol for each horse based on age, environment, travel schedule, and work load of the horse.

Good hygiene including cleaning and disinfecting stalls, equipment and transport vehicles on a regular basis will also help by preventing passing the infection from one horse to another.


Treatment consists of isolating infected horses and initiating good sanitary and hygiene management including disinfecting stalls, equipment, and surfaces that may have become contaminated with nasal discharge, contact with an aborted fetus, or other contaminated areas.

Intensive nursing care is necessary to avoid pulmonary congestion, pneumonia, ruptured bladder or bowel problems. Recovery is often complete, but a small percentage of cases have neurological problems after having the disease

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EquiMed Staff

EquiMed staff writers team up to provide articles that require periodic updates based on evolving methods of equine healthcare. Compendia articles, core healthcare topics and more are written and updated as a group effort. Our review process includes an important veterinarian review, helping to assure the content is consistent with the latest understanding from a medical professional.