Asthma, infection or EMPF caused by EHV-5? – the horse

In the summer of 2021, Jenny Telego, a horse owner in Ohio, noticed that her miniature horse named Dolly was suffering from respiratory problems and a persistent fever. Asthma was the initial diagnosis, but a respiratory infection and pneumonia compounded the condition.

After working with her local vet, Telego took Dolly on her first of four trips to the Galbreath Equine Center at Ohio State University (OSU) Veterinary Medical Center in Columbus.

“Dolly was treated with antibiotics and anti-inflammatories for suspected equine asthma and bacterial pneumonia, but she continued to have frequent bouts of fever and difficulty breathing,” said veterinarian Laura Dunbar-Hostnick, DVM, MS, Dipl. ACVIM, Assistant Professor at the Galbreath Centre.

Dolly did not improve despite diligent treatments and care both at home and at OSU, so Hostnick ordered an x-ray of the mare’s caudal lung (underside and toward the horse’s hindquarters). The results did not look promising – the interstitium pattern remained unchanged due to the treatment for several months.

Dolly continued to experience shortness of breath and an intermittent fever, along with weight loss. In November 2021, she made her fourth trip to Ohio State University, where Telego asked vets to think outside the box to find a reason for Dolly’s worsening condition.

The next step was to withdraw fluid from the lung and test it for herpesvirus 5 (EHV-5). Gamma-herpes virus can be found within lung nodules in horses with equine multinodular pulmonary fibrosis (EMPF).

Dolly’s PCR test came back positive.

At this point, identification of EHV-5 in lower airway or lung tissue samples in horses with imaging signs and abnormalities compatible with EMPF can aid in diagnosis. In addition to severe respiratory distress, horses may also exhibit a cough, nasal discharge, weight loss, and poor body condition.

Hostnik said it’s essential for owners to understand that a positive nasal swab or blood sample in a normal horse or a horse without evidence of pulmonary nodules/fibrosis does not indicate disease and is likely not a cause for concern.

In fact, EMPF is a rare disease. In a Retrospective Study, “Predictive Indices and Long-Term Survival in 14 Horses with equine Multinodular Pulmonary Fibrosis“,” Researchers reviewed 14 cases diagnosed at the University of California, Davis, Veterinary Referral Hospital over an eight-year period. Unfortunately, the long-term prognosis for horses with EMPF, regardless of treatment, is poor. Corticosteroid treatment can improve short-term survival, but the prognosis remains poor.

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