Parker County Today January 2018 - Page 54

our expertise: VET COLUMN Equine Influenza Tom Hutchins, DVM, DABVP North Texas Veterinary Hospital 8283 FM 920 • Weatherford, Tx Dr. Tom Hutchins E 52 quine influenza has a worldwide distribution and is frequently seen in horses transported multiple times a year. Influenza is the most common cause of upper respiratory infections in horses. It has a sudden onset and a short incubation period of 1-3 days. Disease outbreaks usually occur in horses 1-3 years of age. This time generally corresponds with intermingling of horses at show grounds, racetracks and sales. Influenza affects older horses as well but clinical signs are usually milder and may not even be apparent. Although infections can occur at any time of the year, they seem to be more frequent in the winter and spring. Lower humidity and temperatures tend to enhance viral survival. The initial clinical sign that is most evident is the sudden onset of high fever and lethargy. Rectal temperatures can climb as high as 106°F. Cough and nasal discharge accompany the fever but may not appear for several days following the initial fever spike. The cough may persist for up to three weeks. Endoscopic examination of the upper airway reveals pharyngitis and tracheitis. Also the development of myalgia is diagnosed with the reluctance of many horses to move in the course of the disease. The influenza virus belongs to the orthomyxovirus group. It is easily destroyed by common disinfectants like chlorine bleaches. Minor changes in the surface proteins of the virus constitute a “drift” in the makeup of the virus. Major changes in the surface proteins are called a “shift”. Infection in a susceptible horse begins with inhalation of the virus. Incubation time as mentioned previously is 1-3 days. The virus attaches to and proliferates in the epithelial cells of the entire equine respiratory tract. Studies have shown that tracheal mucociliary clearance rates are reduced in horses infected with equine influenza for up to 32 days despite clinical improvement. This damage apparently impairs the transport of mucus in affected animals from the lower airway and predisposes them to secondary bacterial infection. A horse infected with the virus may be unfit for competition from 50 to 100 days. The differential diagnosis that should be considered when a horse develops a fever acutely and has a nasal discharge and cough equine influenza, equine herpes virus 1 & 4, equine viral arteritis, and Streptococcus equi (aka Strangles) infection. A commercially available test detects the virus and requires a nasal swab with results available in as little as 15 minutes. Prevention of equine influenza is vaccination. It has been suggested that upwards of 70 percent of the population should be vaccinated to