A common respiratory disease that occurs in most horse barns is called simply the barn flu by many trainers and owners. There is no such virus as the barn flu but it seems like the flu because horses develop a nasal discharge, fever, sometimes a cough, discharge from the eyes, decreased appetite, swelling in the legs, and sometimes swollen lymph nodes under the throat. All respiratory viruses cause similar symptoms so it is difficult to know which one is involved. The most common upper respiratory viruses are influenza and herpes virus; herpes virus is commonly called rhinopneumonitis. This is confusing because there is another virus called equine rhinitis virus that is not new but is now being considered as more important in the barn flu than in the past.
Some of the studies in respiratory outbreaks are now finding not only influenza but also equine rhinitis virus; this may be the reason horses vaccinated with influenza and herpes virus are still developing respiratory disease. There are two different equine rhinitis viruses called rhinitis A and B. However, rhinitis B has evolved into three different serotypes to make matters even more confusing. This is important because we have a new vaccine for the A strain but not for the B strain. Whether you should consider using this new vaccine depends on whether this disease has caused problems in your horses. When you have a respiratory outbreak, your vet can take samples to determine the cause and if rhinitis virus A is involved, vaccination may be a good idea. Ask your vet about equine rhinitis a vaccine if there is respiratory disease in your barn.