Infectious Respiratory Disease (IURD)
This clinical syndrome refers to infectious diseases that affect the upper respiratory tract of the horse. The upper respiratory tract encompasses from the nasal passages to the larynx. This syndrome occurs worldwide, is generally contagious and can be caused by several viruses and bacteria, such as equine influenza virus, equine herpesviruses, equine adenovirus virus, equine rhinitis viruses and the bacteria Streptococcus equi subspecies equi.
Horses with IURD generally develop a fever, cough, and nasal discharge. They also may demonstrate lethargy, reduced feed intake, and enlarged lymph nodes of the head and neck.
Strangles is a specific type of IURD caused by the bacterium Streptococcus equi subspecies equi. It is the most common infectious disease affecting the upper respiratory tract, and is characterized most often by purulent nasal discharge, and swelling of the lymph nodes of the head and neck. These lymph nodes may rupture and drain pus. Infected horses also may develop other signs such as fever and breathing and eating difficulties.

Non-Infectious Respiratory Disease