Equine multinodular pulmonary fibrosis: a newly recognized herpesvirus-associated fibrotic lung disease.
Authors: Williams K J, Maes R, Del Piero F, Lim A, Wise A, Bolin D C, Caswell J, Jackson C, Robinson N E, Derksen F, Scott M A, Uhal B D, Li X, Youssef S A, Bolin S R
Journal: Veterinary pathology
Summary
# Editorial Summary: Equine Multinodular Pulmonary Fibrosis Progressive fibrotic lung disease in horses has remained largely a clinical mystery, with few cases yielding a definitive diagnosis. This landmark 2007 study established a novel disease entity—equine multinodular pulmonary fibrosis (EMPF)—and identified equine herpesvirus 5 (EHV-5), a previously non-pathogenic gamma-herpesvirus, as its causative agent. Researchers examined 24 affected horses and 23 controls using pathological examination, transmission electron microscopy, in situ hybridization, and PCR detection, finding characteristic nodular fibrotic lesions with interstitial fibrosis, distinctive viral inclusion bodies within macrophages, and EHV-5 nucleic acid present in 100% of affected horses but absent in controls. Whilst EHV-2 co-infection was detected in a third of cases, the species-specific PCR evidence overwhelmingly implicates EHV-5 as the primary aetiological agent. For practitioners managing horses with chronic respiratory disease, cough, and reduced exercise tolerance refractory to conventional treatment, this research provides a pathogenic mechanism and diagnostic pathway—particularly PCR confirmation—that may finally explain previously cryptic cases of pulmonary fibrosis and could ultimately inform therapeutic and management strategies targeting herpesviral infection.
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Practical Takeaways
- •EHV-5, previously considered non-pathogenic, is now recognized as the causative agent of a distinct fibrotic lung disease—consider EHV-5 testing in horses presenting with progressive nodular pulmonary fibrosis and interstitial lung disease
- •This newly described condition (equine multinodular pulmonary fibrosis) should be included in the differential diagnosis for chronic respiratory disease in horses, particularly when standard infectious and inflammatory causes are ruled out
- •Early identification of EHV-5-associated fibrosis may improve management strategies, though treatment protocols for this condition require further investigation
Key Findings
- •EHV-5 detected in 100% (24/24) of affected horses using genus-specific PCR versus 0% in control horses
- •Herpesviral DNA polymerase gene detected in 79.2% (19/24) of affected horses versus 8.7% (2/23) of controls
- •Characteristic gross and histologic findings include multiple nodules of fibrosis throughout lungs with marked interstitial fibrosis and preservation of alveolar-like architecture
- •Viral inclusion bodies identified in macrophage nuclei by transmission electron microscopy, suggesting direct herpesviral association with disease pathogenesis