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Thoughts on Strangles

As I write this article the racetrack at Saratoga, NY has shut down their facility for 2 weeks because of an outbreak of the upper respiratory disease we call strangles.   What we know about strangles today is pretty much what has been known for decades.   Strangles is caused by the bacteria, Streptococcus equi, that has adapted itself specifically to the horse.   People and other animals are not affected by it.

Think about having the absolute worst head cold and sore throat you’ve ever had, with a fever reaching 106 degrees F.   Now imagine that your lymph nodes are 5 times normal size, and you can get some idea of how miserable horses are with this disease.  It’s hard for them to swallow, and even hard for them to breathe.  Horses with acute full blown strangles are in a lot of pain.  The lymph nodes between the lower jaws and around the throat latch get so big that they may rupture, oozing a thick yellow discharge.   Although penicillin is effective against the bacteria, most veterinarians (me included), tend not to use the antibiotic once a horse has the disease because the abscesses are so thick walled that the drug usually doesn’t have an effect.   One belief is that the antibiotic treatment can drive the infection to other parts of the body.   Strangles is mostly an upper respiratory disease.   When it goes to other parts of the body, it is called bastard strangles which can be even more of a problem.

I’ve seen a number of strangles outbreaks in Maine, and would like to share my personal observations about the disease in this state.  The literature reports that the biggest outbreaks of the disease are among weanlings and yearlings.   Taking the nation as a whole, that is true.   That is the most susceptible age group, and outbreaks are common on farms that raise a crop of youngsters for sale each year.   After 6 months the weanlings no longer carry the maternal antibodies from their moms, and so are apt to contract this highly contagious disease.  This is especially true on farms where the barns are crowded and the ventilation is poor.   There are areas of the country where the farms anticipate that each new crop of youngsters will get the bug.

Since we do not have a lot of farms in Maine raising big numbers of foals, almost all of our outbreaks tend to happen in barns when a horse is brought in from a sale or auction barn.   For this reason it is important to isolate any new horse from those sources, and especially those who are stressed by a long (several hours to several days) truck ride.   The literature varies on the time that a new horse should be kept apart, but I like to see at least two weeks in a separate barn or shed with no contact with other horses.   If the horse goes off feed, I recommend taking the temperature twice a day and watching for the telltale swellings. The bacteria are easily carried from horse to horse on hands and clothing.   My suggestion is to feed and take care of the isolated horse after everyone else.   Obviously there can be no shared buckets or equipment.   Even with all these precautions, there is still some risk taking in a horse from a sale barn.   There are asymptomatic horses that carry the bacteria in the guttural pouches deep inside the head and can be sources of infection for long periods of time.

Strangles is rarely fatal, and most horses recover completely.   When it does hit, it often means that an active barn will be shut down for two to three months.   This means no horses in and no horses out.   My experience with the disease is that it doesn’t sweep through and infect all the horses within a short time period.     A slow march through the barn is more typical.    There will be one sick horse, and then a few days or even a week later, another, and so on.   Typically, out of 10 horses 2 or 3 will get very sick, 4 or 5 others just run a fever or have a cough, and 2 or 3 will not be affected at all.   If you do have it on your place, don’t visit other barns without a complete change of clothes and a shower.   You probably wouldn’t be welcome even taking those precautions.   When I know I’m going to an active strangles barn, I make it the day’s last stop and all the clothing from that day goes into the wash, and my footwear gets totally disinfected.

Strangles in a boarding barn often results in a highly charged emotional atmosphere for owner and boarders.  It pays to have as many barn meetings as necessary with all the horse owners and the barn veterinarian to discuss developments as they occur.   Everyone should be allowed to express his or her concerns.   Some of the issues that always arise are:    whose fault this was, who should be moved and where,   who can use common facilities such as the wash rack or the indoor, what is the disinfection protocol, and whether it is or isn’t too late to vaccinate a horse that hasn’t been exposed.

There are two types of vaccinations; one is a killed type that is injected intramuscularly, and the other a modified live vaccine that is squirted up the nose. Every veterinarian has his or her own preference.    The vaccines don’t always completely protect against the disease, but the vaccinated horses usually have an easier time.   Personally I tend to vaccinate those horses at most risk.    For me that means the relatively young horses, and those that are going to be traveling, particularly if they will be stabled at a facility overnight.   When a horse has had the disease, their immunity lasts for years, so I and many other vets do not recommend revaccinating these horses.   On occasion doing so may result in an allergic reaction called Purpura, which is really scary and can be fatal.  You need to rely on you veterinarian’s advice as to which horses to vaccinate, and with which type of vaccine.   It would be a mistake not to rely on your veterinarian when dealing with an outbreak, as each is different and needs to be handled with their expertise.


David A. Jefferson, DVM

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