Uh Oh, the Coggins test is positive!


You read that correct! A positive Coggins test. For most of the horse-owning world, this is a theoretical problem they will never encounter. However, for a group of horses in Canada, this is reality right now. So let’s chat about Coggins. What it tests for, what it means to have a positive test, and what happens to those horses next.


Can I study for a Coggins test?


Well, you can, but it won’t do you any good. A Coggins test is a simple blood draw (from your horse, just to be clear). That blood is then tested for the presence of the Equine Infectious Anemia Virus (EIAV). This is a particularly nasty virus. EIAV is a very close relative to the AIDS virus, and works in much the same way. EIAV can spend years wandering around a horse’s body without any signs or symptoms of its presence. During that time, however, an infected horse can spread the virus if it is bitten by one of several different species of flies. The most common fly vectors are what are known as the dirty eaters: horse flies, deer flies, and other things you humans would call huge flies.


It’s positive! Now what???


This is what has happened in two areas of Canada recently. Horses had Coggins tests performed in anticipation of competitions, and those tests came back positive! The next step will be to quarantine all the horses on these farms. Once a good quarantine is in place, investigators will start trying to determine if horses have traveled to or from these farms, and if they could be out spreading EIAV. In the meantime, on the farm, all the horses will have Coggins tests performed, including the positive horses, who will be retested. Then everyone who is negative gets retested every 60 days until no new cases show up on that testing, plus a few months quarantine for good measure.


What happens to the positive horses?


Horses who repeatedly test positive, unfortunately, must be isolated from other horses for the remainder of their lives, or be euthanized. To ensure that no one sells the horse as normal, a large brand is placed on the left side of the neck, ending in the letter A. This tells everyone at a glance that this horse tests positive for Coggins.

Good news on the quarantine: it’s a pretty small area. Horses only need to be about 200 yards from any other horse to prevent the spread of the disease. So, it is feasible to quarantine a horse, but it isn’t easy. If horses are quarantined, it’s likely they will live many years with very few side effects of the virus. Eventually it will begin to attack the immune system and lead to life-threatening anemia.


Fun Coggins Trivia


  • Coggins testing was begun in 1972. At that time nearly 4% of horses tested were positive. For the last year I could Google about (2005), 0.01% of Coggins tests were positive.
  • 95% of positive tests in the United States have come from Southeastern states. As you all know, we grow big flies really well.
  • USDA thinks about 40% of the horse population of the United States gets tested in any given year
  • Federal, State, and Local governments use the number of Coggins tests performed in an area to estimate horse numbers. This is important! They use that number to decide if money should be spent to create, maintain, and improve horse stuff.


Coggins is an example of testing that works for everyone! By testing the horses that travel, the number of positive horses has dropped pretty dramatically! The recent positives in Canada prove we have to keep testing though, to make sure this disease doesn’t catch us by surprise!

Until next week!!



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