Last week we encountered our first strangles outbreak of the year. As you probably already know, Strangles is highly contagious upper airway infection. Horses rarely die from this disease, though on rare occasion it can be deadly. They do, however, get very sick from it. Typically affected horses have very large lymph nodes under their jaw that get so large they can ‘strangle’ their upper airway—thus the name. After a couple of days, the lymph nodes will break open and drain.
The disease is caused by a bacteria named Strep. equi ssp. equi. This bug is easily spread from one horse to another, usually through nose to nose contact or by sharing water buckets or a common water tank. It is possible for people to carry this bug around on them and transmit it from an infected horse to another horse. Because of the highly contagious nature of this disease, quarantining affected individuals and good hygiene practices are necessary to limit its spread. Horses can continue to shed the bacteria (and thus infect other horses) for up to 6 months after they have recovered. The only way to tell for sure if they are still shedding the bacterial is to get a swab of the back to the throat and send it into a lab.
Immunity to this disease is not life long, even after a clinical infection. Affected horses usually have immunity for 18-24 months. There are several different vaccines available for this disease. The one we are currently recommending is an intra-muscular injection. There is also an intra-nasal vaccine available. Great care must be exercised when handling and administering the intra-nasal product. Protective immunity from the vaccines are probably 6-12 months, at best.
The best way to prevent the disease is to quarantine new horses coming into the barn. A two week quarantine period is usually sufficient. During the quarantine period, the horse should be kept away from direct contact with other horses and not have access to a common water source or share water buckets with other horses. Also, the quarantined horse should be handled and fed, after all the other horses are first tended to.
Aside from quarantining, or preventing exposure, vaccination is the best tool we have to prevent this disease. We recommend strangles vaccination if you take your horse to barns or shows where they are stabled with other horses of unknown background or if there is a lot of traffic of new horses through the barn. When you go to shows or other organized horse events, do not let your horse share water buckets or hay bags with other horses.