Page 10 - 22 February 2013

ONGOING STUDY REVEALS RISK
FACTORS FOR EQUINE INFECTIOUS
UPPER RESPIRATORY DISEASE
Seasonality, age and stress play a role in horses’ susceptibility to respiratory disease.
by Craig Barnett, D.V.M., Senior Equine Technical Services Veterinarian for Merck Animal Health
“We are still seeing cases of all four primary respiratory pathogens.”
Cold winter followed by rainy spring weather can create the perfect storm for an infectious upper respiratory disease (IURD) outbreak.
Many horse owners will be moving their young horses to indoor facilities for training and sale preparations. Subsequently, horses that are already more susceptible to IURDs due to their age are exposed to environ- ments with a lower air quality and more irritants, such as dust and ammonia. In addition, the stress
of training could lead to an increased potential for a respiratory outbreak.
THE LATEST IURD RESEARCH
A recent study at the University of California- Davis that was funded by Merck Animal Health revealed that in fact, this perfect storm plays a role in the risk of an IURD outbreak. In this study, veterinar- ians throughout the United States were enrolled in
a voluntary surveillance program. The veterinarians were asked to collect blood and nasal secretions from their equine patients that presented signs of acute IURD and/or acute onset of neurologic disease. A total of 761 horses, mules and donkeys were enrolled and tested via real-time PCR testing for the four major IURD pathogens: Equine Herpesvirus - 1 (EHV-1); Equine Herpesvirus - 4 (EHV-4); Equine Influenza virus (EIV) and Streptococcus equi subspecies equi.
“The initial results of the surveillance study were very helpful in our ability as an industry to better understand the prevalence of infectious upper respira- tory diseases but also helped the participating veterinar- ians provide a more timely and accurate diagnosis for their patients, which can be especially helpful during
an IURD outbreak situation,” said Nicola Pusterla, D.V.M., Dipl. ACVIM, Department of Medicine and Epidemiology at the University of California-Davis and lead investigator and author on the biosurveillance study.
SEASONALITY
During the 24-month duration of the study, the majority of the IURD cases were seen during the fall, winter and spring months. The highest detection rate of the four pathogens was EHV-4 and was primarily seen in the fall and winter. The second highest detec- tion rate was EIV, which was mainly seen during the winter and spring months. S. equi, the third-highest
detection rate, was primarily seen during the winter and spring, and EHV-1 was mainly seen during the fall and spring months.
“While the seasonality of IURDs has been reported in other studies, this study should serve as a reminder on the importance of biosecurity and appro- priate vaccination recommendations during the fall, winter and spring months,” Dr. Pusterla said.
AGE MATTERS
Much like children, younger horses are more susceptible to contracting a respiratory disease and should be considered at moderate- to high-risk for IURDs and be vaccinated and managed accordingly. Of the 761 horses enrolled in the study, 385 (50.6 percent) were less than 5 years of age, with 130 (17.1 percent) less than 1 year of age. The highest frequency of EHV-4 was seen in horses 1 year of
age or less. This was followed by the second-highest frequency of EIV seen in horses 1 to 5 years of age.
One vaccine option that should be considered for all horses that are at higher risk for contracting equine influenza, including older foals, yearlings and young horses is Flu Avert® I.N. This modified-live intranasal EIV vaccine manufactured by Merck Animal Health is the only influenza vaccine that requires only one dose for primary immunization. Challenge studies con- ducted by HGG Townsend with this vaccine support an onset of immunity of 5 to 7 days in naïve horses1. Considering cell-mediated and serologic anamnestic responses as well as mucosal responses, the onset of immunity with this vaccine in primed horses would be expected to be even sooner. This evidence provides for the use of this vaccine in an outbreak situation to help reduce occurrence, severity and duration of disease. Flu Avert® I.N. can also be especially useful for the older foal’s first EIV vaccine because all other EIV vaccines require a two-dose series over a 4- to 6- week period to achieve optimum immune response.
Additionally, EIV is one of the seven diseases included in Merck Animal Health’s Equine Vaccine Performance Guarantee, which reimburses reasonable diagnostic and treatment costs, up to $5,500, for a spe- cific lack of vaccine efficacy to any properly vaccinated horse. For additional details on the Equine Vaccine Performance Guarantee, contact your veterinarian.
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SPEEDHORSE, February 22, 2013
VETERINARY VIEWS