Experimental induction of pulmonary fibrosis in horses with the gammaherpesvirus equine herpesvirus 5.
Authors: Williams Kurt J, Robinson N Edward, Lim Ailam, Brandenberger Christina, Maes Roger, Behan Ashley, Bolin Steven R
Journal: PloS one
Summary
# Editorial Summary: EHV-5 and Equine Pulmonary Fibrosis Equine herpesvirus 5 (EHV-5), a gammaherpesvirus, has long been suspected in cases of equine multinodular pulmonary fibrosis (EMPF), but direct experimental proof was lacking until this landmark 2013 study. Researchers inoculated EHV-5 isolated from naturally affected horses into the lungs of healthy animals and tracked viral presence, immune response, and histopathological changes over time using PCR, virus isolation, immunohistochemistry, and quantitative lung collagen analysis. The inoculated horses developed nodular pulmonary fibrosis with substantially elevated lung collagen (80 µg/mg versus 26 µg/mg in controls; p < 0.5) and increased interstitial collagen deposition (32.6% ± 1.2% versus 23% ± 1.4%; p < 0.001), whilst virus proved difficult to isolate despite successful detection of viral antigen in lung tissue. This work provides the first direct evidence that EHV-5 can induce fibrotic lung disease in its natural equine host, with the intriguing implication that fibrosis develops during latent rather than active viral replication—a finding that may explain why affected horses often show progressive clinical decline long after initial infection and underscores the importance of considering EHV-5 serology and antigen detection in cases of chronic respiratory disease.
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Practical Takeaways
- •EHV 5 is confirmed as a causative agent of equine multinodular pulmonary fibrosis; screening and monitoring may help identify affected horses earlier
- •The chronic nature of EHV 5-induced fibrosis (progressing while virus remains latent) suggests EMPF may be difficult to reverse once established—early intervention and biosecurity are critical
- •Consider EHV 5 as a differential diagnosis in horses with progressive respiratory disease and pulmonary fibrosis, particularly in herd situations with respiratory history
Key Findings
- •EHV 5 inoculation induced nodular pulmonary fibrosis and myofibroblast induction in experimentally infected horses
- •Mean lung collagen was significantly elevated in EHV 5-infected horses (80 μg/mg) compared to controls (26 μg/mg, p<0.5)
- •Interstitial collagen was significantly increased in infected horses (32.6% ± 1.2%) versus controls (23% ± 1.4%, p<0.001)
- •Virus was difficult to detect throughout the experiment despite EHV 5 antigen presence in lungs, suggesting latent infection induces fibrosis