Researchers Review Equine Multinodular Pulmonary Fibrosis

While EMPF is considered a rare disease, researchers found that it appears to be related to a very common one.

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Since it was first identified in 2007, deadly equine multinodular pulmonary fibrosis (EMPF) has been reported in numerous horses across North America and Europe. While still considered a rare disease, EMPF appears to be related to a very common one—equine herpesvirus (EHV)—and early treatment appears to be the main hope for survival.

Specifically, it’s the “gamma” herpesviruses that seem to be involved in EMPF development, explained Bianca Schwarz, PhD, DVM, Dipl. ECEIM, head of the Internal Medicine Service in the Equine Clinic of Altforweiler, Germany, and a former researcher at the Equine Clinic of the University of Vienna in Austria. There are two known gamma herpesviruses in horses: EHV-2 and EHV-5. These EHV forms often go unnoticed in horses, as the infection can be subclinical (i.e., it doesn’t cause outward clinical signs). But if signs do occur, they are usually related to the respiratory tract, causing nasal discharge or breathing difficulties, and in more severe cases fever and lethargy. There is no vaccine for EHV-2 or -5.

Here’s how it all ties together: In all documented EMPF cases, the affected horses have also tested positive for EHV-5, Schwarz said. And about one-third of those horses tested positive for EHV-2, as well. Schwarz says that, even so, EMPF itself cannot be considered a “viral” disease: “At the moment we think that it is a wrong immunoreaction of certain horses to a viral pathogen,” she said.

Looking at five of the seven EPMF cases seen in two European referral clinics between late 2008 and mid-2011, Schwarz and colleagues noted two distinct forms of EMPF: “discrete” and “diffuse.” In EMPF, the lungs develop fibrosis nodules—a kind of bumpy scarring—in the alveoli. The alveoli are tiny pockets in the lungs that receive the incoming air during breathing and process its gases for the body to use. In the discrete form of EMPF, nodules can range from small to very large (up to 6.5 cm in Schwarz’s case studies) and are sharply defined in the lung tissue. By contrast, in the diffuse form the nodules are mostly small and widespread. In the current study three of the horses had the discrete form, whereas the other two had the diffuse form

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Passionate about horses and science from the time she was riding her first Shetland Pony in Texas, Christa Lesté-Lasserre writes about scientific research that contributes to a better understanding of all equids. After undergrad studies in science, journalism, and literature, she received a master’s degree in creative writing. Now based in France, she aims to present the most fascinating aspect of equine science: the story it creates. Follow Lesté-Lasserre on Twitter @christalestelas.

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