Etiology

Equinegammaherpesvirus type 5, belonging to the genus Percavirus, family Herpesviridae,has been associated with equine multinodular pulmonary fibrosis, a disease thataffects adult horses sporadically and progressively.

Epidemiology

The virus hasa worldwide distribution with high prevalence, it has been detected both inhealthy animals and in animals with clinical signs. The infection usuallyoccurs in young animals, but later than in the case of equine herpesvirus type2 and the infection usually lasts over time.

Pathogeny

Infection withthis virus usually does not produce clinical signs. The infection is producedby inhalation of viral particles, which replicate in the mucosa of the upperrespiratory tract and invade the B lymphocytes that spread the infectionthrough the rest of the organism.

Clinical signs

The clinical signs derived from equine herpesvirus type 5 infection are fever, cough, nasaldischarge, tachypnea, tachycardia, weight loss and intolerance to exercise.

Diagnosis

The clinical diagnosis consists of observing the presence of the clinical signs described above, together with a compatible radiographic image. The definitive diagnosis is made by microscopic study of the pulmonary lesions (interstitial fibrosis, type II hyperplasia of alveolar epithelial cells, presence of inflammatory cells and macrophages with intracytoplasmic inclusions), together with PCR of the affected lung tissue to demonstrate the presence of the virus. These two techniques require samples that are obtained invasively, which is why viral detection is also performed by PCR in bronchoalveolar lavage, although positive results do not always correlate with the presence of this disease. In those horses in which the techniques mentioned above cannot be performed, detection by PCR in blood and nasal secretions can be done. In the post-mortem analysis of pulmonary tissue, nodular fibrosis or consolidation by coalescence of interstitial fibrosis foci can be observed.

Treatment

At present, no specific treatments have been described for this disease, which has a chronic and progressive character.

Prevention and control

It is a virus with ubiquitous distribution, so no vaccines have been developed against it.

Public Health Considerations

This virus is specific to its host, affecting only equids.

References

• Equine InfectiousDiseases. 2014 Elsevier Inc. ISBN: 978-1-4557-0891-8
• Updateon Viral Diseases of the Equine Respiratory Tract
• Gammaherpesvirusesand Pulmonary Fibrosis: Evidence From Humans, Horses, and Rodents
• ExperimentalInduction of Pulmonary Fibrosis in Horses with the Gammaherpesvirus EquineHerpesvirus 5
• Assessment ofquantitative polymerase chain reaction for equine herpesvirus-5 in blood, nasalsecretions and bronchoalveolar lavage fluid for the laboratory diagnosis ofequine multinodular pulmonary fibrosis