Rhinopneumonitis

Most horses develop this common respiratory infection at some point in their lives, but you’ll want to take steps to limit the risks of serious consequences.

- Laurie Bonner

Rhinopneumonitis (“rhino”) in horses is roughly equivalent to the common cold in people---it is a highly contagious respiratory infection spread by a virus that passes readily from horse to horse. An outbreak can spread quickly and easily through a herd. Signs range from mild to severe and might include fever, lethargy, cough and nasal discharge. There is no specific treatment, but most horses recover completely within a week or two with rest and supportive care, which might include drugs to lower a high fever as well as antibiotics if secondary infections set in.

But unlike the common cold, rhino has a dark side: It is caused by one of two types of equine herpesviruses, EHV-1 and EHV-4. Some strains of each organism can pass beyond the respiratory system and affect other parts of the body. If the virus infects the epithelium that lines the uterus, it can trigger abortion. The fluids from a lost pregnancy contain a large quantity of virus, which can easily be picked up by other mares in a field, potentially leading to “abortion storms” that sweep quickly through a herd.

Some strains of EHV-1 and -4 can also cause equine herpesvirus myeloencephalopathy (EHM), an inflammation of the blood vessels that supply the brain and spinal cord. Affected horses develop neurological signs, including altered gaits, ataxia, a floppy tail and urinary leakage. With supportive care, most horses who are able to remain on their feet are likely to make a full recovery from EHM. Outcomes are generally worse for those who become recumbent, although horses may recover with intensive care, which can include the use of support slings.