Equine veterinarians report of prevalence of certain equine pathogens

DAVIS, CALIF. — In a first study of its kind, veterinarians across the country reported on the prevalence of certain common pathogens among the equine population.

Specifically, veterinarians collected blood and nasal discharges from 761 horses with acute infectious upper-respiratory-tract disease and/or acute onset of a neurological disease. The findings were published in the July 2011 issue of the Veterinary Record journal.

"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," says lead study author Nicola Pusterla, DVM, Dipl. ACVIM, of the University of California-Davis School of Veterinary Medicine.

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.

The study, which started in 2008, is still ongoing and is supported by Merck Animal Health (formerly Intervet Schering Plough).

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).