TEXAS VET NEWS By Dr. Bob Judd, DVM and the Texas Farm Bureau Texas Farm Bureau Radio Network

In previous programs, I have discussed herpes virus vaccines, West Nile virus vaccine, and influenza vaccines in horses, and today I am going to talk about another recommended vaccine.  There are three strains of viral encephalitis that affect horses and they are Eastern, Western and Venezuelan.  These three strains of encephalitis are caused by a virus and are transmitted by mosquitos, and every horse in Texas should be vaccinated for at least the Eastern and Western strains every year.  The Venezuelan strain of encephalitis has not been seen in the United States since 1971 and so many vets do not vaccinate for it anymore.  Killed vaccines are commonly used for encephalitis in the United States and the labels recommend using these vaccines once yearly.  However, some studies have shown the immunity of these vaccines to be very short lived and many practitioners, especially those in Florida, recommend vaccinating for the eastern strain every 4 months. 

Another vaccine that should probably be used once yearly is tetanus.  Horses are susceptible to tetanus and studies have shown the tetanus toxoid vaccine to be effective for at least a full year.  In humans, tetanus vaccine lasts up to 10 years and the vaccine probably lasts longer than 1 year in the horse.  However, since we don’t have evidence to prove that fact, it is recommended to give the vaccine once a year.  There is also some confusion among owners regarding tetanus vaccine as there is also a tetanus antitoxin.  This vaccine should be used only when a horse has never been vaccinated and is injured.  It is important to know that tetanus antitoxin only lasts about 10 days and not one year like tetanus toxoid.         

Date Published: 7/6/2009 10:12:00 AM