Etiology

Equinegammaherpesvirus type 2 has been associated with keratoconjunctivitis,respiratory signs and dermal disease in horses. It is a virus with greatgenetic variability, coinfections have been described with various strains inthe same animal and also with equine gammaherpesvirus type 5.

Epidemiology

The virushas a worldwide distribution with high prevalence, having been detected both inhealthy animals and in animals with clinical signs. The infection usuallyoccurs at early ages (animals <2 months). As with other members of thefamily, the virus can establish a permanent infection or remain latent,reactivating in times of immunosuppression such as those associated withtransport stress. It is described a case of an aborted fetus that had viralparticles in the lung, so the virus would be able to cross the placentalbarrier.

Pathogeny

Its role as a pathogen is unclear due to the high prevalence in the equine population and its association with a wide variety of clinical signs. The infection is caused by inhalation of viral particles that infect the cells of the nasal mucosa and the upper respiratory tract, as well as the B lymphocytes. When the B lymphocytes enter the blood circulation, the infection spreads throughout the body. It has in its genome several genes with immunomodulatory character that interact with the immune system of the host and can produce immunosuppression.

Clinical signs

In foals, infection with EHV-2 has been associated with pharyngitis, lymphadenopathy, rhinitis, nasal discharge, cough and fever. In adult horses, it presents with involvement of the upper respiratory tract, inappetence and poor performance. Keratoconjunctivitis has been described in both adults and foals, characterized by dotted or branched superficial lesions accompanied by blepharospasm, epiphora, chemosis and hyperemia. A case of oral and esophageal ulcers has been described in a one-month-old foal and a case of granulomatous dermatitis in an adult horse, in which this virus has been isolated from the lesions.

Diagnosis

The diagnosis of the virus is complicated due to the variety of clinical signs that have been associated with it and because the virus has been isolated both in animals with clinical signs and healthy, not being able to establish a direct relationship between the presence of the virus and disease. The diagnosis can be done by PCR, viral isolation and detection of viral particles by immunohistochemistry.

Treatment

In cases of respiratory disease the treatment is symptomatic, until signs resolution is achieved. Treatment in cases of keratoconjunctivitis consists of topical antivirals such as idoxuridine or trifluridine, combined with systemic non-steroidal anti-inflammatory drugs.

Prevention and control

Although some vaccine has been described, vaccination against this virus is not widespread due to its ubiquitous nature and lack of evidence of its pathogenic nature.

Public Health Considerations

This virus affects only equids, therefore it’s not considered zoonotic.

References

• Update on Viral Diseases of the Equine Respiratory Tract
• Isolationof equine herpesvirus–2 from the lung of an aborted fetus
• Equidherpesvirus 2–associated oral and esophageal ulceration in a foal
• EquineHerpesvirus 2-Associated Granulomatous Dermatitis in a Horse
• Keratoconjunctivitisin a group of Icelandic horses with suspected g-herpesvirusinvolvement