Based on an article in "Hoof Beats" magazine, 1997, Frank Lampley, PA.
The horse industry is being plagued by one epidemic after another, everything from a pharyngitis epidemic, viral respiratory infections, East and West Nile, herpes and other outbreaks still to be diagnosed. Some are seasonal and some are regional, but ultimately no one is safe and it doesn't matter where you are. Contagious diseases strike when and where they want, every horse is susceptible from coast to coast.
Can ANTIBIOTICS help?
No! They are absolutely worthless against viruses. You need laboratory tests, which can cost hundreds of dollars, to diagnose the type of infection. If it is determined to be a virus, all antibiotics are useless. Even when it turns out to be something other than a virus and treated with antibiotics there is an increased chance of relapse, because the antibiotics have weakened the horse's immune system. The immune system is an effective defense mechanism and the only defense in case of a viral infection. Furthermore, the horse's digestive system depends heavily on a certain types of bacteria that colonize the gut. This is called a bacterial flora, some call them "good bacteria", which help with the breakdown of nutrient, which are then absorbed into the blood stream. Of course, as the immune system and digestive tract is taxed to the max, opportunistic other infections often like to sneak in and take a hold of your horse... this is on top of the nasty virus it already caught. So, what now?
Combating Infectious Disease