The decision to vaccinate for strangles can be complicated. In the past strangles was not as prevalent as it is now. Today virtually anyone that travels with horses is at risk of exposure and development of the disease. The vaccine we currently use is an attenuated live strain of the bacterium that causes strangles, Streptococcus equi var. equi, and the vaccine is given intranasally. This strain does not cause clinical disease but does stimulate an immune response that can be assessed by measuring antibody levels. Occasionally, following vaccination, a horse may develop one of the rare, immune-mediated complications of strangles, i.e. purpura hemorrhagica. This is a form of vasculitis or inflammation of the blood vessels and can result in swollen limbs and eyelids.
Given this risk, some have recommended that owners measure antibody levels prior to vaccination and not vaccinate horses with high antibody levels. In practice this recommendation is problematic because the test can be quite expensive and results can take weeks. Adding a farm-call and this pre-vaccination blood draw to the yearly routine care program can quickly add up financially. Therefore, it is often more practical to simply vaccinate considering complications from the vaccine are very, very rare (only 2 have been seen by Mid-Rivers in the last ten years).
A new test is being developed to measure antibody levels to assess the horse’s risk and may alter the approach to vaccination when available. If such a test becomes widely available, reasonably priced with rapid accurate results, we may re-evaluate our recommendation.