Equine herpesvirus-5, which had previously been reported in horses in the United States, is also present in the European horse population, researchers recently reported. They found the virus in horses without any signs of disease (known as subclinical infection) and those with various respiratory signs or fatigue.

"EHV-5 is more or less considered as an immune-modulating actor capable of interacting with the inflammatory pathways of the host (the infected horse)," said study coauthor Guillaume Fortier, DVM, MS, of the Frank Duncombe Laboratory in France. "It has been recently associated with a deep pulmonary disease: equine multinodular pulmonary fibrosis."

As part of his PhD work on horse gamma-herpesvirus and subclinical respiratory disease, Fortier and his colleagues looked at samples from more than 650 horses to see if EHV-5 was common in the respiratory tract of horses in Europe and to find out if the virus caused airway inflammation.

"Airway inflammation is costly for the horse industry, and recent research pointed out the potential role of this virus in this subclinical infection. We decided to investigate the potential implication of this lesser known equid herpesvirus," he said.

They found that EHV-5 lodges deep in pulmonary tissue and can cause respiratory disease in horses.

Because it can also exist in horses without any signs of disease, it has the potential to spread easily from one horse to another. There is no vaccine or treatment for EHV-5 so early detection is the best way to protect horses and prevent disease, he said.