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Horse Tick Disease: Anaplasmosis

Updated: Apr 17, 2023

It's winter but the ticks are going strong! And boy oh boy did I find this out first hand!

Day before sickness hit!

As you can see from the picture above my girls were acting normal and enjoying the warm weather, but Golan (horse on the right) became a totally different horse the following day.

It's November here in New England and it should be in the 50's but we have been getting bits of warmer than usual weather. The day she started to be off was an unbelievably warm day here! It was in the 70's and sunny! When I got Golan from her field, I thought maybe she was warm from the high temperatures and her thick winter coat. But then as I watched her more, I started to get the sense it was something else.

You're not warm you're sick!

When I watched Golan her breath was rapid. Her nostrils were flaring and she did not want to move. I walked her to some shade out on the grass but she would not touch it at all! She loves her grass, so immediately my heart dropped. I brought her into the barn and she nibbled a little bit on some loose hay but was not eager. It was then I called the vet and took her temperature. My heart dropped again when I saw the thermometer reading at 104F.

The vet was on some other calls and was not going to reach us for a couple of hours. So I put her into the indoor ring with some water, loose hay and got a bucket to sponge her to help her body cool. Sometimes she seemed more like herself and other times she looked so uncomfortable.

When the vet came he did a full check up. Her heart was beating rapidly, breathing fast and her temperature had now spiked to 106F. He immediately took blood for some tests but said she looked exactly how other horses who are dealing with anaplasmosis look like. I had known another horse who had it before so I knew it could look bad but was treatable.

For those of you who do not know what anaplasmosis is, let me give you a definition!


Anaplasmosis (formerly called equine granulocytic ehrlichiosis) is an infectious disease caused by the rickettsial agent Anaplasma phagocytophilum that is transmitted through ticks! Many cases occur here in the United States but some have been found in other countries. They call it a seasonal disease but at this point with our unusual temperatures in the winter we are seeing this disease at all times of the year.

A horse with this disease is not contagious to other horses or people. However people can get this disease too if they are bitten by an infected tick, so do check yourself for ticks too!


This disease can affect horses of all ages and some may show only certain symptoms.

  • fever

  • picky or poor appetite

  • depression

  • jaundice

  • limb swelling

  • reluctance to move

  • in severe cases you can see incoordination/ataxia

Nibbling here and there, waiting for the vet.


The vet explained to me it can be hard to accurately test for anaplasmosis since the organism will not always show up. But that they would run a few test to see if anything else showed up or if she had Lyme. But no matter what he was going to start treating her.

This is the common protocol vets follow when they think a horse has anaplasmosis. Treat the horse now and wait for the test results after. Some will do a blood smear, titers and other blood work to try to find the organism but again it can be tricky to find!


Early treatment is important in making sure the horse recovers well. Vets will usually administer a tetracycline antibiotic and some fever relief medicine.

Our vet gave her an injection of oxytetracycline to attack the disease and a banamine injection to help with the fever. The following day we would start giving doxy powder for a week or so and give banamine paste for 3 days. He told us we may see some swelling in her limbs and she still may not want to move much but that will get better over time. Also when we start riding again she may get tired fast and that it will take time for her energy levels to go back to normal. Lastly the most interesting thing he told us was that with horses who run high fevers like her, after he gives them the intravenous doxy, many will start to sweat a lot!

And I am not even joking but maybe 15 minutes after the vet left she started sweating and became herself again! I took her outside for the breeze and she started eating the grass ferociously and she even rolled because she was so wet from the sweat! We happily dried her off and put her back out with her buddies to get some rest!

Sweating it out and eating grass!


Once antibiotics are started improvement will occur in 48 hours. For us it was improvement in 15 minutes and she has fully recovered since! Her blood work was pretty normal except for a low red blood cell count which he said was common in horses with anaplasmosis. And the good side effect from the recovery is that horses have immunity for up to 2 years! This makes me very happy for her but also very worried about my other mare who did not got this and fingers crossed never does!


Currently there are not any vaccines for this disease. The best we can do is check our horses daily for ticks and use fly spray or other products that offer tick protection!

I hope this information has helped you and if your horse is dealing with this right now, I wish them a speedy and easy recovery!

If you need support or want to talk about this, feel free to reach out!



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