Equine Respiratory Biosurveillance: What Have We Learned? 

snotty horse nose closeup
horse with respiratory disease
The voluntary equine respiratory biosurveillance program includes samples from horses with an elevated temperature and at least one clinical sign of respiratory disease, including nasal discharge. Amy Dragoo

Since 2008, Merck Animal Health has conducted a voluntary equine respiratory biosurveillance program, in conjunction with private veterinarians, to study the prevalence and epidemiology of relevant viral and bacterial respiratory pathogens. This program has increased awareness of respiratory pathogens in the veterinary community, provided invaluable epidemiological information pertaining to common and less characterized respiratory pathogens and provided equine influenza virus sequence data to monitor how the virus is changing and to evaluate and improve vaccine efficacy.

As a veterinary profession, management of infectious disease is one of the most consistent challenges we face. Ongoing surveillance is an extremely important tool to monitor emerging trends, manage disease outbreaks and improve preventive strategies.

Voluntary Equine Respiratory Biosurveillance Program

The voluntary equine respiratory biosurveillance program was born through the vision of two individuals and conversations that took place almost 17 years ago between D. Paul Lunn, BVSc, MS, PhD, MRCVS, Dipl. ACVIM—current Dean of the University of Liverpool’s School of Veterinary Science—and D. Craig Barnett, DVM—retired Director of Equine Veterinary Professional Services at Merck Animal Health. In late 2007, a partnership was formed between Merck Animal Health and the University of California, Davis School of Veterinary Medicine that established UC Davis, led by Nicola Pusterla, DVM, DACVIM, AVDC-Equine, as the program’s real-time PCR laboratory for sample submissions.

In March 2008, the biosurveillance program came to fruition as the Infectious Upper Respiratory Disease Study. The goals of the study were four-fold. First, to provide participating veterinarians with a valuable diagnostic tool to assist in providing accurate and timely diagnosis to treat and manage infectious respiratory diseases. Second, to provide the equine industry with a better understanding of the prevalence and epidemiology of common respiratory pathogens. Third, to identify and monitor the current circulating strains of major equine respiratory pathogens. Lastly, to evaluate the efficacy of current vaccination protocols.

Today, this program has resulted in one of the largest equine infectious upper respiratory biosurveillance data sets. This comprehensive, ongoing national surveillance study monitors equine herpesvirus types 1 and 4, EIV, Streptococcus equi subspecies equi (S. equi; the cause of strangles) and equine rhinitis A and B viruses. 

Sample Submission Parameters

To date, more than 11,000 samples have been voluntarily submitted from veterinarians across the United States. To be included in the study, samples must have been obtained from a horse with a temperature greater than 101.5° F and that exhibited at least one of the following clinical signs: nasal discharge, cough, lethargy or central nervous system abnormalities. Submissions consisted of two nasal swabs collected from one nostril and a completed questionnaire. Samples were shipped overnight to the UC Davis laboratory for next-day quantitative PCR testing.

Data Results

This dataset has generated several scientific publications and presentations. Additionally, the data has been used to provide biannual reports to participating veterinarians that bring new information to the forefront and provide timely updates to share with horse owners. Since 2008, results of this surveillance program have yielded insight into the prevalence and seasonality of these important respiratory pathogens. Of samples in which equine respiratory pathogens were detected, EHV-4 was the most common (representing 31% of positive samples) followed closely by EIV (29%) and S. equi (22%). 

In the United States, EIV peaks annually in March with broad occurrence in winter and spring, and EHV-4 occurs more commonly in the fall from September to November. Most importantly, all diseases occurred throughout the year and should not be excluded due to seasonal expectations

It is critical for veterinarians and horse owners to understand the importance and value of identifying the pathogen(s) associated with respiratory outbreaks. Not only can this data lead to more effective treatments and biosecurity decisions, it helps the entire horse industry better prepare for future challenges.

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