In a study supported by Merck Animal Health (formerly Intervet Schering Plough) which started in 2008 and is ongoing, lead study author Nicola Pusteria, DVM, Dipl. ACVIM of the School of Veterinary Medicine at the University of California, Davis, launched a nation-wide inquiry into the presence of common pathogens among the equine population.
Veterinarians throughout the country were asked to collect blood and nasal discharges from horses with acute infectious upper-respiratory-tract disease and/or acute onset of a neurological disease and report on the prevalence of certain common pathogens among the equine population.
The findings were published in the July 2011 issue of the Veterinary Record journal.
According to Dr. Pusteria, "The surveillance program presented here allowed us to study the epidemiology of these pathogens and served the equine community by quickly confirming the presence of a contagious pathogen and instituting measures to prevent disease spread."
Veterinarians were asked to respond to a questionnaire about the equine cases and respective clinical symptoms. Real-time polymerase chain reaction was used to test samples to detect equine herpesvirus-1, equine herpesvirus-4, equine influenza virus and Streptococcus equi subspecies equi.
"The short turn-around time and reliability of real-time PCR makes this molecular technology an ideal tool for the diagnosis of infectious respiratory pathogens," says Pusterla.
Over a two-year study duration, 201 index cases (26.4 percent) tested PCR-positive for one or more of four pathogens. EHV-4 was detected most frequently (82 cases), followed by EIV (60 cases), S. equi subspecies equi (49 cases) and EHV-1 (23 cases). A total of 15 horses presented with two infections; one horse had three infections.
Criteria affecting detection rates for the pathogens included season, breed and age of affected horses.
What took researchers by surprise with regard to study findings was the lack of vaccination history in almost half of the horses, according to Pusterla.
Based on the results of the program, Pusterla says that veterinarians can apply the findings of the surveillance to practice through increased awareness and testing of horses with signs of infectious upper-respiratory diseases.
Going forward, Pusterla says, "The next step is to find out if there are other less well characterized respiratory pathogens responsible for infectious upper respiratory diseases (EHV-2, EHV-5, adenovirus type 1, equine rhinitis virus A and B).