A voluntary biosurveillance program has allowed for the study of 10,296 horses with respiratory tract infections over the last 13 years in the United States.
Researchers discovered that the bacterial or viral cause of illness was only able to be determined in 23.8 percent of horses suffering from acute onset of fever and upper respiratory tract issues. The cause of issues in the remaining 76.2 percent of horses was never determined.
Respiratory diseases are one of the most prevalent issues in young performance horses and often cause horses to miss training and competitions. Veterinarians often struggle to determine whether respiratory infections are viral or bacterial; this is an important distinction because the treatment for each type of infection differs.
Lead researcher Dr. Nicola Pusterla noted that unknown viruses could have been responsible for respiratory disease in some of the inconclusive cases, but added that there is a need to investigate the nature of novel viruses and their association with clinical disease.
It's not uncommon for horses to travel around the world for competition and sport, increasing the risk of pathogen transmission, as evidenced by recent EHV outbreaks. Determining the factors for upper respiratory tract disease and the factors for each pathogen can not only help to determine the nature of infection, but also how to control its spread.
The researchers used molecular-based quantitative polymerase chain reaction (qPCR) testing to determine whether equine influenza virus (6.8 percent), equine herpesvirus-1 (0.7 percent), equine herpesvirus-4 (6.6 percent), equine rhinitis A and B viruses (2.3 percent), or S. equi (4.7 percent), which causes strangles, were present.
The team learned that most of the respiratory infections were found in colder months; viral infections were found in younger performance horses (4 years old and younger) and strangles was most often found in older pleasure horses (5 years old and older).
Clinical signs included fever (73 percent), nasal discharge (67.8 percent), lethargy (65.3 percent), poor appetite (53.8 percent), and coughing (43.5 percent). Coughing was most common with equine flu.
Nearly one-third of all cases were vaccinated against equine flu and/or equine herpesvirus-1 and 4, though vaccination against S. equi was uncommon.
Study results do not offer conclusive data to determine whether an illness was caused by a virus or bacterium. Diagnostic testing is still necessary.
Read the study here.
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