What Is the Treatment for Potomac Horse Fever?

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  • Written By: Rebecca Harkin
  • Edited By: Melissa Wiley
  • Last Modified Date: 13 January 2020
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Potomac horse fever is treated with a course of the antibiotic oxytetracycline. Horses infected with this illness are also frequently given fluid replacement therapy as well as electrolyte replacement therapy when diarrhea is severe. Non-steroid anti-inflammatory drugs may also be administered to manage a painful hoof condition often associated with this sickness. Vaccines against this medical condition are available, but complete immunity is not always achieved with the vaccine.

Treatment of Potomac horse fever is fairly successful if the infection is caught early, so it is important for a groom to be aware of the symptoms. A horse suffering from this infection will typically eat less feed, have a fever, and have either a decrease in waste production or will have diarrhea. Other symptoms may include depression, swelling, and laminitis, a condition where the circulation to the hooves is decreased, causing swelling and lameness. Potomac horse fever may also cause an expecting mare to abort her fetus.

Once a groom observes any of these symptoms, the veterinarian should be called immediately. A preliminary diagnosis will be made based on symptoms exhibited by the horse and the prevalence of Potomac horse fever in the area. Confirmation of the diagnosis can be done using a real-time polymerase chain reaction to amplify the bacteria’s deoxyribonucleic acid. This test should be performed on both blood and stool samples.


This infection is caused by a fairly virulent bacterium known as Neorickettsia risticii. This bacterium is capable of evading detection by the immune system, so it does not provoke an immune response by the horse’s body. The bacterium accomplishes this feat by hiding inside macrophages, a cellular component of the immune system capable of destroying extrinsic matter, such as bacteria. As a result, the immune system is unable to identify the Neorickettsia risticii as a foreign entity and mount an immune response.

Oxytetracycline is used to treat an infection of Potomac horse fever. This antibiotic is effective because it prevents Neorickettsia risticii from stealthfully hiding inside macrophages. Horses are also usually treated for dehydration with fluid replacement therapy and, when necessary, electrolyte replacement therapy. If the horse is also suffering from laminitis, a non-steroidal anti-inflammatory may be given to manage the animal’s suffering.

A vaccine against Neorickettsia risticii is available. The efficacy of the vaccine, however, is incomplete. Often, vaccinated horses will still get sick and, due to partial immunity, the symptoms may be less noticeable or harder to read. The limited effectiveness of the vaccine may be due to the different strains of this bacterium that have been isolated.


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