Animal Stewardship
Respiratory Disease in Horses: Common Types, Significance and Prevention By: Bryant Craig, DVM, Merck Animal Health Runny nose, fever, cough, fatigue. Respiratory disease complex – we see it in our cattle, but it’s also commonly found in our horses. Infectious upper respiratory disease can have significant consequences for our horses’ health, and come in several forms. The most common causes in the horse include equine influenza virus (EIV), equine herpesvirus (EHV) – also known as rhino – and Streptococcus equi subspecies equi (S. equi) – better known as strangles. In a nationwide surveillance study by Merck Animal Health, equine influenza and equine herpesvirus type 4 (EHV-4) are diagnosed more frequently than strangles and EHV-1. Some of the biggest risk factors are travel, exposure to new horses and environments, and stress from training or work pressure. These are challenges that all feedlot animals encounter. Vaccination coupled with good husbandry is the most economical and effective way to protect these individuals. Equine Influenza Virus Equine influenza virus is one of the most common infectious upper respiratory diseases of the horse. It is widespread in the equine population of the United States and throughout the world. It spreads quickly because the incubation period is only 24 to 48 hours, and the virus can be
transmitted through the air. In fact, coughing can spread nasal droplets more than 200 yards. Horses that are sick for the first time can shed the virus in nasal secretions for as long as seven to 10 days. Indirect transmission of the virus can also occur via hands, clothing and common use articles such as bits, brushes and buckets. Recovering horses require a minimum of three weeks of rest or at least one week of rest for every day of fever. Premature return to exercise may be associated with complications including secondary bacterial infections, reactive airway disease and exercise intolerance. Once thought to be a disease primarily of the young, Merck Animal Health has discovered through its ongoing respiratory disease surveillance program (conducted in partnership with University of California, Davis) that EIV is common in broader age groups, as well. Study data shows positive cases in horses ranging in age from 8 months to 22 years. The equine influenza virus is constantly undergoing change (known as antigenic drift), and the latest changes seem to have made older horses more susceptible to the disease. A strict vaccination protocol incorporating the modified live EIV vaccine (Flu Avert® I.N.) coupled with good biosecurity measures is the best method of prevention of equine influenza. pacdvms.com 23
