Infectious Respiratory Disease: PCR Testing Suggested (AAEP 2010)

Polymerase chain reaction (PCR) is a fast, accurate, quick, and easy testing method to diagnose pathogens associated with equine upper respiratory tract infections, and researchers on a recent study recommended that veterinarians pursue PCR in cases of infectious upper respiratory disease. Not only does it allow the veterinarian to pinpoint the causative pathogen, it also can help control the spread of the pathogen.

"Infectious respiratory diseases are the most common medical conditions treated by ambulatory veterinarians throughout the country," explained Nicola Pusterla, DVM, PhD, Dipl. ACVIM, associate professor at the University of California, Davis, School of Veterinary Medicine, who presented the study on the use of real-time PCR at the 2010 American Association of Equine Practitioners Convention, held Dec. 4-8 in Baltimore, Md. "Many of these respiratory infections have similar clinical presentations (e.g., fever, nasal discharge, coughing, etc.) and many horse owners and vets often do not pursue diagnostics when dealing with single cases. However, determining the exact causative agent(s) associated with infectious upper respiratory tract diseases is essential in order to prevent outbreak and minimize spread."

Real-time PCR is a reliable diagnostic laboratory technique with a quick turnaround time (i.e., results are generally available within 24 hours) that can help veterinarians diagnose infections caused by equine herpesvirus (EHV)-1 or EHV-4, equine influenza virus (EIV), and Streptococcus equi subsp. equi.

Pusterla and colleagues set out to determine the benefits of PCR by testing 761 horses with signs of acute respiratory infections or acute neurologic signs. With PCR they were able to successfully identify DNA from one or more of the pathogens EHV, EIV, or S. equi subsp. equi in 201 (26.4%) of the tested horses. Of these 201 horses, there were:

  • 82 EHV-4 infections;
  • 60 EIV infections;
  • 49 S. equi subsp. equi infections; and
  • 23 EHV-1 infections.

Fifteen horses had double infections and one horse was infected with three of the four disease-causing organisms.

"Testing and knowing the exact cause of the respiratory infection is essential for implementing proper management practices and to help control the spread of disease," concluded Pusterla.

Disclaimer: Seek the advice of a qualified veterinarian before proceeding with any diagnosis, treatment, or therapy.