Upper respiratory infections whose symptoms include fever, snotty nose, and cough is a common problem in horses, particularly the young adult that travels to shows or rides. The most common causes are a handful of virus groups and the bacteria Streptococcus equi which is responsible for Strangles. The virus families include influenza (flu), rhinoviruses, several Herpes viruses (rhinopneumonitis), adenoviruses, and less commonly the Equine Arteritis Virus (equine viral arteritis or EVA).

These infections occur wherever horses congregate and young horses are especially susceptible. Though rarely fatal, these diseases count for tremendous loss of time and money in the horse business. These diseases have very similar symptoms but it is important to make an attempt to identify the cause. If strangles is identified early it is treatable. There are complications to some herpes virus infections, particularly EHV-1, that you do not see with the other diseases.

This article discusses how these upper respiratory diseases spread, the symptoms, palliative treatment and nursing care, prognosis, and prevention. The emphasis of this article is to try to differentiate the possible cause of the infection based on the above characteristics and then provide a link to the specific disease where more specific therapy can be instituted.

Horses get exposed and contract colds and flus throughout their life but most effected are young adult horses and perhaps the aged horse. The primary way horses get upper respiratory infections is by coming in contact with nasal or oral secretions. These may be aerosolized by sneezing or coughing or come into contact with contaminated surfaces. Communal water and food buckets are particularly good at transferring infection. However different types of infection behave differently when it comes to spread.

The influenza virus is highly contagious and spreads rapidly through the barn with up to 100% infected. The virus does not live outside of the host for anytime, so direct contact with infected horses is the most likely way a horse gets infected. Once infected with influenza horses stay contagious for seven to 10 days. The virus does not seem to persist in the stable for any time following resolution of the acute stages in the horses.

The herpes virus is a little more complicated. Following infection horses continue to shed the virus for up to several weeks following resolution of any clinical signs. Not as contagious as influenza, herpes infection may persist in a stable for months, with occasional new cases, before it burns out. Following infection and recovery horses probably carry the herpes virus for the rest of their life. Usually these horses are not contagious unless stress of other unknown factors cause a resurgence of the disease. These recurrences may be subclinical so horses can be contagious without showing signs of disease but spreading to naive horses, which get a full blown URT infection. The herpes virus is a little hardier and may live for a time in the environment or inanimate objects.

The strangles organism is much hardier and may persist in the environment of the horse for a month or more. There are also known carriers of the Strangles organism who are contagious but do not show disease. Horses coming into barns or pastures with past history of Strangles may become infected despite it having been a long time since the last infection.

For more on each of these disease see the specific articles.