This morning the vet came to give five of the horses - Pie, Dawn, Sugar, Scout and Misty - their intranasal strangles vaccine. The other three horses - Fred, Fritz and Charisma - use two different vets, and I believe they will also come shortly to do the strangles vaccinations. We usually do our first round of spring vaccinations (5-way: Eastern and Western encephalitis, tetanus and flu/rhino; and West Nile booster) towards the end of March, followed a bit later by the rabies and strangles vaccinations.
We've moved up our timing on the strangles vaccinations because we're taking some extra precautions due to Drifter's expected arrival in the second half of March. It turns out he may very well have had a relatively mild case of strangles about nine months ago. He lives in a small herd totaling three horses, and last May a mule was added to the herd. The mule was apparently somewhat of a rescue and came in with a bit of a snotty nose. After that, two of the three horses, including Drifter, developed what was quite likely strangles. Neither horse was terribly sick - they'd all been vaccinated - but that's what the vet thought it was although no culture was done to confirm it. Drifter did have a small abscess in his throat that burst. Both horses made a good recovery - they had a complete course of penicillin and were closely monitored - and neither has shown any sign of illness since. Drifter seemed very healthy to me when I saw him last fall, and my vet will check him over very carefully during the prepurchase exam.
I've learned a lot about strangles and its transmission over the last several weeks. Here's some good information and here's some more information. The last time I'd seen a horse who became sick with it was around 1970 when I was a teen and my horse Snow developed a full-blown case - this was in the days before vaccines - including the very enlarged abscessing glands that are typical of the disease. Strangles is a form of strep that is specific to horses, and it is very contagious although not all that persistent in the environment. The likeliest means of transmission is nose-to-nose contact and contamination of shared water tanks. Most horses, even those who get full-blown cases, recover well. The disease can be a threat to very young horses and horses with compromised immune systems, and there are occasional serious complications.
The introduction of vaccines, first an intramuscular one (with some risk of abscesses at the injection site) and then the intranasal one, is a very good thing, although I have learned that the vaccines have relatively poor efficacy and may not prevent infection in all cases. Vaccination does, however, reduce the risk of infection and also will likely reduce the severity of symptoms in a horse that does become infected, so it is advisable. Our vet recommended that Pie be revaccinated even though he was vaccinated for strangles about five months ago.
Most horses, once fully recovered, no longer can transmit the disease. Horses should be considered still potentially contagious for 6 to 8 weeks after they are fully recovered. And a very small percentage of horses may become silent carriers of the disease, although most of these do show some symptoms - typically infectious nasal discharge.
I've also learned that most vets recommend that a horse who has had strangles should not be vaccinated for at least a year after having strangles - there's a very nasty complication that can arise, called purpurea hemorrhagica, which is an antibody/antigen auto-immune reaction leading to generalized swelling of the blood vessels - it's extremely painful and can cause serious damage to the horse. This complication can arise for other reasons too, but vaccination after a horse has had strangles is one cause. A significant percentage of horses with strangles will have life-long immunity to it, but many do not. A blood titer to determine antibody levels should be done before vaccinating a horse who has had strangles.
Both Drifter's owner and I have talked to our vets and I have also spoken to the University of Wisconsin veterinary clinic. Due to his treatment with a full course of penicillin and apparent full recovery and good health (to be confirmed by my vet at the prepurchase), the likelihood that he is a carrier is very low. There are tests to determine carrier status - involved repeated deep intranasal swabs under sedation - but these tests are more reliable in detecting carriers immediately after infection and also fail to detect carriers in a number of cases, so we have decided not to do them.
The recommendations we received were to isolate Drifter in a separate paddock for three weeks after his arrival and to revaccinate all our horses at least three weeks before he is directly introduced to them. If he were a carrier, the stress of the long trailer ride and the move to a new barn would likely provoke new symptoms - fever and/or a snotty nose. Then it would be possible to culture any nasal discharge, and treat him with antibiotics if needed. In fact, we really should have been isolating any new arrival to our barn for two to three weeks anyway and have never done so. Although we've never had problems in the past, this is a practice we should probably use in the future. While he's in isolation, I'll still be able to work with and ride him, just not in close proximity to other horses, and we'll take appropriate precautions like keeping his equipment and supplies separate and avoiding cross-contamination.
All these precautions are probably unnecessary, but worth taking in our opinion.
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On another equine health note, our main veterinary practice is holding a client education seminar tonight on worming practices - and they'll be providing free fecal testing of one horse for each person who attends (and bringing a sample qualifies you for door prizes!). Apparently over 100 people have signed up - there's so much interest there's actually a waiting list - it's very good that they're doing this and the degree of interest in the local horse community is great. I'll let everyone know what they have to say.