Investigation of Selected Prevalence Factors Associated with EHV-2 and/or EHV-5 Infection in Horses with Acute Onset of Fever and Respiratory Signs

The purpose of this study was to determine any associations of EHV-2, EHV-5, and dual infection with EHV-2/-5 with demographic parameters, clinical signs, and coinfection with other common respiratory pathogens. Nasal swabs collected from 9737 horses were tested for EHV-2 and EHV-5, as well as EHV-1, EHV-4, EIV, <i>S equi</i>, ERAV, and ERBV, by qPCR. Clinical signs and demographic parameters were recorded, and prevalence factors were evaluated for significance regarding EHV-2 and/or EHV-5 infection. Out of the 9737 horses in this study, 17.8% tested EHV-2-positive (<i>n</i> = 1731), 15.8% tested EHV-5-positive (<i>n</i> = 1536), 33.4% tested positive for both viruses EHV-2/-5 (<i>n</i> = 3247), and 33.1% tested negative for both viruses (<i>n</i> = 3223). When comparing EHV-2 and/or EHV-5 infected horses to horses testing qPCR-negative for both viruses, horses infected with EHV-2 alone were more likely to be younger Thoroughbreds with a history of recent transportation, presenting with fever, and having a higher rate of coinfections with EHV-4 and <i>S. equi</i>. Horses infected with EHV-5 alone were less likely to be used for pleasure purposes, had fewer clinical signs, and were more likely to be coinfected with EHV-4. Horses dually infected with EHV-2 and EHV-5 were much more likely to be younger, used for competition, presenting with a fever, and coinfected with additional respiratory pathogens. It is apparent from the study population that horses infected with EHV-2 alone or in combination with EHV-5 had breed predilections, greater frequency of clinical signs, and a higher rate of coinfections with EHV-4, ERBV, and <i>S. equi</i>.