EHV-5 associated with respiratory disease in a survey of alpha- and gamma herpesviruses in 409 Australian horses

Reasons for performing study:

To determine the prevalence of EHV-1, -2, -4 and -5 in respiratory samples from a large number of horses using quantitative PCR methods. Samples from horses with, and without mild signs of respiratory disease provided an opportunity to examine associations with single or multiple herpesviral infections.

Objectives:

To determine any correlation between quantitative detection of these equine herpesviruses and mild clinical respiratory disease in horses.

Methods:

Nasal swabs were taken from horses with, and without, clinical respiratory disease. Nucleic acid was extracted from all swabs prior to PCR testing for EHV-1, -2, -4 and -5. Clinical signs of respiratory disease included coughing, fever (temperature >38.5°C) or nasal discharge.

Results:

Of the 409 horses, 250 (61%) were clinically normal, 121 (30%) presented with clinical signs consistent with mild respiratory disease and 38 (9%) horses had no traceable clinical history. One-fifth (83/409) of horses sampled were infected with EHV-2 and almost twothirds 249/409 (60.9%) with EHV-5. Infection with EHV-5 was significantly associated with mild respiratory disease (85/121; 70.2%) compared to nondiseased horses (137/249; 55%) P = 0.005. The proportion of EHV-2 infected horses, however, did not differ significantly between those in the diseased (18/121) and nondiseased (61/250) groups. Too few horses were detected with alphaherpesviruses to determine any association with clinical signs of disease. Mean nasal shedding loads of herpesviruses were not significantly different between diseased and nondiseased horses.

Conclusions:

There was a significant association between horses displaying clinical signs of mild respiratory disease and infection with EHV-5, however, no such association was evident for neither horses with EHV-2 nor the alphaherpesviruses EHV-1 and -4. The clinical significance of respiratory gammaherpesvirus infections in horses remains yet to be determined; however, these findings add to the mounting body of evidence incriminating EHV-5 in association with equine respiratory disease