When preparing for vaccinations, it’s helpful to know what a horse has been vaccinated for in the past. If a horse’s vaccination history is unknown, it’s best to assume that he has not received any vaccinations at all and use the protocols designed for unvaccinated horses, which might include boosters of some vaccinations. Additional doses of most vaccinations will not harm a horse, reports EQUUS magazine.
The strangles vaccine is the one exception: it should not be given if a horse’s vaccination history is unknown. In rare cases, horses that have had strangles before and those that have been repeatedly vaccinated for the disease may have a serious complication called purpura hemorrhagica if they are vaccinated again, according to Dr. David Horohov of the Maxwell H. Gluck Equine Research Center in Lexington, Ky.
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Purpura hemorrhagica is an immune reaction that causes the blood vessels in the head, legs, and abdomen to swell. This condition is painful for the horse as circulation is impaired. Horses with purpura hemorrhagica can be very depressed and it can take a long time for the swelling to abate. Purpura hemorrhagica can be fatal if it isn’t treated effectively or in a timely manner.
Though the risk of purpura hemorrhagica is small, it’s best to pull a strangles titer on a horse with an unknown history. The titer will show if a horse carries antibodies to Streptococcus equi. If he does show titers, he doesn’t need to be vaccinated again.
Read more at EQUUS magazine.
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