Have you ever wondered what the most common clinical signs of respiratory diseases in American horses might be? Or whether your horse’s age, or simply the time of year, could make him more likely to contract an infectious respiratory pathogen? The answers you’re looking for might finally be here. The first two years of results are in from an ongoing surveillance study at the University of California, Davis (UC Davis), School of Veterinary Medicine, that examines the prevalence of respiratory pathogens in U.S.-based horses.

In the study 95 veterinary practices in 23 states collected blood and nasal secretions from equids with acute infectious upper respiratory signs. For each horse, donkey, or mule with respiratory signs (including fever, depression, nasal discharge, coughing, or anorexia), veterinarians filled out a questionnaire and sent blood and nasal samples to UC Davis for PCR (polymerase chain reaction) analysis.

Of the 761 horses with clinical signs of acute respiratory disease from March 2008 to February 2010, 26.4% (201 horses) tested positive for one or more of four common respiratory pathogens: equine herpesvirus, types 1 and 4 (EHV-1 and EHV-4, respectively), equine influenza virus (EIV), and Streptococcus equi subsp. equi (strangles). Of these four, EHV-4 had the highest detection rate (82 cases), followed by EIV (60 cases), strangles (49 cases), and EHV-1 (23 cases). Fifteen of those 201 horses tested positive for two pathogens, and one was infected with three of the four.

The remaining 76.3% (560 horses) did not test positive via PCR for any of the four pathogens included in the study