May 2022

Animal: Horse, Warmblood, 12 years old, female

Organ: Lung

History: Owner noticed progressive emaciation 3 months ago. After 1 month, fluctuating hyperthermia with general weakness and tremors appeared. Radiographs showed multiple pulmonary nodules. The animal did not respond to symptomatic treatment and its condition progressively declined, leading to euthanasia for humane reasons.

Ancillary tests: Blood analysis showed neutrophilia, lymphopenia, hyperfibrinogenemia, hypoalbuminemia, α2-, β2- and γ-hyperglobulinemia and low iron levels. Pulmonary biopsy revealed alteration of the normal architecture with alveolar-like spaces lined by cuboidal epithelial cells and containing degenerate neutrophils, sloughed epithelial cells and macrophages. The interstitium was markedly enlarged by fibrosis with numerous fibroblasts, neutrophils and macrophages. Very rare alveolar macrophages had a glassy eosinophilic intranuclear inclusion body.

Main macroscopical main findings: Lungs were diffusely red and numerous spherical masses up to 6 cm in diameter, firm and paler than the adjacent parenchyma, were felt by palpation and seen when cutting the parenchyma. There was no evidence of neoplasia in other organs.

Diagnosis: Equine multinodular pulmonary fibrosis.

Comment: Equine multinodular pulmonary fibrosis (EMPF) is a rare disorder affecting lungs of horses at all age. The etiologic agent is thought to be Equid Herpesvirus 5 (EHV-5) but co-infection with Equid Herpesvirus 2 (EHV-2) has been observed in up to 20% of cases. A similar condition has also been described in donkeys. In our case, two PCR were performed on broncho-alveolar lavage fluid but were negative for EHV-5. Despite these negative results, gross and histopathological findings were considered to be typical of EMPF in this case.


MARENZONI ML., PASSAMONTI F., LEPRI E., CERCONE M., CAPOMACCIO S., CAPPELLI K., et al. Quantification of Equid herpesvirus 5 DNA in clinical and necropsy specimens collected from a horse with equine multinodular pulmonary fibrosis. J Vet Diagn Invest. 2011, 23, 802-806.

SCHEURER L., BACHOFEN C., HARDMEIER I., LECHMANN J., SCHOSTER A. Prevalence of Nasal Shedding of Equid Gammaherpesviruses in Healthy Swiss Horses. Viruses. 2021, 13, 1686.

WILLIAMS KJ., MAES R., DEL PIERO F., LIM A., WISE A., BOLIN DC., et al. Equine multinodular pulmonary fibrosis: a newly recognized herpesvirus-associated fibrotic lung disease. Vet Pathol. 2007, 44, 849-862.

WONG DM., BELGRAVE RL., WILLIAMS KJ., DEL PIERO F., ALCOTT CJ., BOLIN SR., et al. Multinodular pulmonary fibrosis in five horses. Journal of the American Veterinary Medical Association. 2008, 232, 898-905.

Picture: Marine Le Dudal, Ecole Nationale Vétérinaire d’Alfort (EnvA), Maisons-Alfort, France.