Potomac Horse Fever Symptoms, Diagnosis, And Treatment

Last Updated on September 10, 2022 by admin

Knowing the main Potomac horse fever symptoms to look out for can help you to spot this disease in the early stages. Let’s find out everything you need to know about Potomac horse fever symptoms, diagnosis, and treatment!

What Is Potomac Horse Fever?

Potomac horse fever (PHF) is a potentially fatal disease of horses caused by infection with a bacteria called Neorickettsia risticii. This disease is now commonplace in most US states, as well as some areas of Canada, South America, Europe, and India.

The transmission of this bacteria is very complex, as it lives inside the cells of a host animal. This is normally an insect found near waterways, such as a mayfly or caddis fly. Horses can contract PHF when they accidentally consume the host animal, which is why this disease is more common in horses that graze near water.

PHF can affect horses of any age or breed, although it is rarely seen in horses less than one-year-old. It cannot be transmitted from horse to horse, and cases tend to be sporadic in nature.

When a horse is infected with Neorickettsia risticii the bacteria begin to infect the cells that line the intestines, particularly the large colon. This causes inflammation of the colon, known as colitis.

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Potomac Horse Fever Symptoms

The main symptoms of Potomac horse fever are those that occur as a result of colitis. The inflammation of the large colon means that it can no longer function normally, and the horse will develop chronic diarrhea. The colon also has a reduced ability to absorb nutrients, causing the horse to lose weight.

Most horses with PHF will develop a fever, as part of the immune response to the infection. The horse will be dull and lethargic and may have a reduced appetite.

In some cases, the horse will develop laminitis, which is thought to be linked to the high levels of endotoxins caused by the infection. The main symptoms of laminitis manifest as a reluctance to move or walk on hard ground, lameness, warm feet, and increased digital pulses.

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Potomac Horse Fever Diagnosis

Potomac horse fever can appear to be very similar to several other equine gastrointestinal diseases, so laboratory tests are required to confirm a diagnosis. These tests may include taking a sample of the horse’s blood, feces, or both.

There are two types of tests for PHF, a blood antibody test and a PCR test of the blood or feces. Raised levels of antibodies can indicate recent exposure to PHF, but do not confirm that this is the cause of the symptoms shown by the horse. A PCR test is more accurate, as this confirms that the infectious agent is currently present within the horse’s body.

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Potomac Horse Fever Treatment

The main focus of treating PHF is to provide supportive care and tackle the source of the infection. Antibiotics will be given to kill off the infectious agent, and the horse may need to be hospitalized in a specialist equine veterinary clinic while these take effect.

Because horses with PHF normally suffer from profuse diarrhea and weight loss, they will often require intravenous fluid therapy and electrolyte supplementation to prevent dehydration. They may require a specialist diet to help maintain the body weight.

Non-steroidal anti-inflammatory medication is administered to reduce fever and help prevent endotoxemia.

As horses with PHF are prone to laminitis, preventative therapies are used to protect against this. These include the use of ice boots to keep the hooves cool, and frog supports to prevent sinking or rotation of the pedal bone.

Potomac Horse Fever Symptoms

PHF is not transmissible between horses, so contact between infected and non-infected animals does not need to be limited. Preventing PHF in horses can be tricky, with the best course of action normally recommended is to limit access to waterways during the summer months. It is also advisable to take steps to limit the number of flying insects inside barns and stables.

A vaccination is available against PHF and is advised in areas where the disease is prevalent. It does not give complete protection against PHF, but clinical signs are said to be reduced and the prognosis improved in vaccinated horses.

Summary, Potomac Horse Fever Symptoms

So as we have learned, the most common Potomac horse fever symptoms include diarrhea, weight loss, fever, and reduced appetite. If you suspect that your horse has Potomac horse fever, blood or fecal test will be taken by your veterinarian to confirm the diagnosis. Horses with PHF will need to be treated with antibiotics and supportive nursing care.

We’d love to hear your thoughts about Potomac horse fever symptoms, diagnosis, and treatment! Have you ever come across an outbreak of this disease in a herd of horses? Or maybe you’ve got some questions about the best treatment for Potomac horse fever? Leave a comment below and we’ll get back to you!


How do you treat Potomac horse fever?

Potomac horse fever is treated with antibiotics, anti-inflammatories, intravenous fluid therapy, and anti-diarrhea medication. It is commonplace for horses with PHF to need a period of hospitalisation and intensive nursing care to facilitate a full recovery. If left untreated, potomac horse fever can lead to secondary laminitis and endotoxaemia, and may lead to fatality of the horse.

Is Potomac fever in horses contagious?

Potomac horse fever is an infectious disease, but it cannot be passed from horse to horse. It is transmitted by a bacterial agent that lives inside cells of insects commonly found near water, such as mayflies. The risk of contracting PHF can be reduced by restricting access to waterways during the warmer months of the year.

What is the agent that causes Potomac horse fever?

Potomac horse fever is caused by an intracellular bacteria, Neorickettsia risticii, that colonises the cells of insects such as mayflies and caddis flies, plus a number of other host animals. It causes disease in horses when these insects are accidentally eaten.

How common is Potomac Horse Fever?

The prevalence of potomac horse fever varies widely according to the country and region. It is now found in most US states, but is much more common in some than others.