Two Cases of Equine Multinodular Pulmonary Fibrosis in Japan.

This research paper reports on the first cases of Equine Multinodular Pulmonary Fibrosis (EMPF), a disease associated with equine herpesvirus type 5 (EHV-5), in Thoroughbred horses in Japan. The findings and diagnoses were based on physical and microscopic examination of the horses’ affected lungs.

Introduction to EMPF and EHV-5

• Equine Multinodular Pulmonary Fibrosis (EMPF) is a relatively newly classified type of interstitial pneumonia – an inflammation of the lung tissue surrounding the air sacs.
• The disease is closely associated with Equine Herpesvirus type 5 (EHV-5), a species of virus that affects horses.
• EMPF has previously been reported in North and South America, Europe, and Oceania. This research paper presents the first known cases in Japan.

Diagnostic Findings and Analyses

• Two Thoroughbred horses in Japan were diagnosed with EMPF. The diagnosis was based on both gross and histopathological findings.
• Gross lesions, significant physical abnormalities seen with the naked eye, were found in the horses’ lungs. These consisted of numerous firm and merging nodules, distributed widely throughout the lungs. These nodules were less than 3 cm in diameter and pale white to tan in color.
• On a microscopic level, these nodules presented severe interstitial fibrosis (scarring between the lung tissues) and infiltration of macrophages, neutrophils, lymphocytes, and a few eosinophils (various types of immune cells).
• Remaining alveoli, the tiny air sacs in the lungs, were lined by cuboidal epithelial cells (type II pneumocytes) and filled with macrophages. In rare instances, these macrophages displayed oval intranuclear inclusion bodies which appeared eosinophilic to amphophilic (pink-blueish in color when stained).
• A polymerase chain reaction test, a method used to amplify small segments of DNA, and sequence analyses were conducted and identified the glycoprotein H gene of EHV-5 in the samples. Further testing using in-situ hybridization confirmed the presence of EHV-5 in the alveolar macrophages within the lesions.
• In one of the cases, electron microscopy revealed particles akin to herpesviruses, and EHV-5 was further isolated from the pulmonary lesions, consolidating the diagnosis of EHV-5 associated EMPF.