SUBTLE EHV THREATS STUDIED
Equine herpesvirus (EHV) types 2 and 5, which are not generally associated with disease themselves, may make a horse more susceptible to respiratory illness after long trailer rides, according to a study from Australia.
Five EHV strains are well known for infecting horses: Types 1 and 4 primarily affect the respiratory tract, leading to coughing, nasal discharge and fever. Type 1 can also cause abortion. EHV type 2 is generally not known to cause disease but is thought to suppress the immune system. EHV type 3 causes coital exanthema ---blisters or spots in the external genital region. EHV type 5 was only recently identified as a potential contributor to lung disease.
To explore whether transport affects susceptibility to or reactivation of EHV, researchers at the University of Sydney took nasal swabs from 12 horses prior to, immediately following, and then one and five days after an eight-hour trailer ride. They then tested each sample for the presence and quantity of EHV using polymerase chain reaction (PCR) technology. Blood was also drawn before and after the trailer ride to test for EHV-1 and -4 antibodies. Tracheal endoscopy and washes were also performed to look for signs of infection and inflammation.
The PCR tests showed no evidence of EHV-1 or EHV-4 before or after the trailer rides. In five of the seven horses already positive for EHV-2, however, levels of that strain increased after transport. In addition, seven of the 11 horses testing positive for EHV-2 carried strains that were similar to those infecting other study horses, suggesting the organisms may have been transmitted during the trailer ride. In one horse, the virus was genetically different prior to and after transport, suggesting reactivation of a latent infection. Four of nine horses who were positive for EHV-2 or -5 prior to transport showed signs of airway inflammation afterward.
The researchers conclude that transport encourages increased shedding, transmission and reactivation of EHV-2 and -5. They call for recognition of the role of these EHV strains in transport-related disease.
Reference: “Equine transport and changes in equid herpesvirus’ status,” Frontiers in Veterinary Science, September 2018