What causes Rocky Mountain Spotted Fever in Dogs?

The three species of ticks that most commonly become infected and spread this disease are found most frequently in the southern New England coastal states, areas of the mid-Atlantic, western central states, and southern Atlantic states.

In these areas of the United States, Rocky Mountain Spotted Fever (RMSF) is considered endemic, as it is regularly found to infect dogs and people.

The American dog tick, the Rocky Mountain wood tick, and the brown dog tick are responsible for transmitting the R. rickettsii bacteria in North America. R. rickettsii bacteria enter the cells that line blood vessels and reproduce there. The infection of these cells causes local damage and activates platelets that can lead to bruising.

Symptoms of Rocky Mountain Spotted Fever in Dogs

Unlike cats, dogs are extremely susceptible to clinical infection with the R. rickettsii bacteria. For the R. rickettsii bacteria to be passed on to a dog, the infected tick(s) generally need to be feeding for 5-20 hours. Symptoms of the infection may develop within 2 days to 2 weeks.

Early signs of the disease may include:

• Enlarged lymph nodes
• Lack of appetite
• Fever (as high as 105 degrees F)
• Polyarthritis (inflammation of multiple joints) and resulting lameness
• Respiratory issues (difficulty breathing, coughing)
• Painful abdomen
• Gastrointestinal signs (vomiting and diarrhea)
• Swelling (edema) of the face and feet/legs

In severe cases the following signs may be seen:

• Pinpoint bruising of mucous membranes (gums, inner surface of the lips, and pink portion of the eyes)
• Altered mental states
• Increased sensitivity (pain) along the spine
• Unsteady gait
• Seizures
• Nose bleeds
• Gangrene (tissue death of extremities due to blood vessel damage and lack of blood flow)
• Organ failure and resulting death

Diagnosing Rocky Mountain Spotted Fever in Dogs

As the symptoms seen in dogs with this disease can be associated with many other illnesses, your vet will need to perform multiple tests. The results of these tests will help determine the underlying cause of the illness.

After performing a thorough physical exam, your vet will recommend blood work, possibly urine tests, and x-rays. The bloodwork may show signs of low or high white blood cell count (depending upon the stage of the disease – early or late). There may also be a decrease in the platelets and red blood cells indicating potential clotting issues and anemia. In addition, the blood work may show changes to the blood protein level, calcium, electrolytes, and kidney and liver values.

None of these blood work changes clearly point to a diagnosis of RMSF. Because of this, it is important for veterinarians to be aware of any travel to RMSF endemic areas or potential tick exposure.

The gold standard test to confirm a diagnosis of RMSF is an Indirect Immunofluorescent Assay (IFA) test. The RMSF IFA test requires that two blood samples be submitted for testing. The first blood sample is drawn when the dog is ill, and the second sample is drawn a couple of weeks later.

The IFA test measures the amount of antibodies to RMSF in the dog’s bloodstream. Rocky Mountain Spotted Fever is diagnosed if there is an increase in the dog’s antibody level (titer) that is 4 times greater in the second sample than the first.

There are other tests (PCR or testing of spinal fluid) that can be run to look for RMSF but they are not as accurate.

Treatment of Rocky Mountain Spotted Fever

As RMSF can cause severe and even life-threatening disease, it is important for treatment to be started even before a definite diagnosis is made.

Antibiotics, usually doxycycline, are the preferred treatment for Rocky Mountain Spotted Fever. This antibiotic is usually prescribed for 1-3 weeks of treatment, depending on the dose.

There are a couple of other antibiotics that may be chosen to treat the disease but may have downsides (frequency of dosing, side effects, etc.). Your vet will make treatment recommendations and discuss the options with you.

Is treatment for RMSF in dogs successful?

If treatment is started early in the disease, dogs typically recover fully, and many develop life-long immunity. In dogs where the disease is caught early, the symptoms usually improve within the first 1-2 days of treatment.

However, if proper treatment is delayed orocky mor the dog has a heavy R. rickettsii count, the prognosis worsens. In cases of severe illness (organ failure or extreme symptoms), your dog will typically need to be hospitalized at first. If the dog’s condition can be stabilized, they can then return home and receive continued treatment there.

Severely affected dogs may not respond to treatment at all. Fatality rates from this disease are expected to be between 1-10% of the dogs who contract Rocky Mountain Spotted Fever.

Prevention of Rocky Mountain Spotted Fever

• Limit exposure to ticks, especially in endemic areas of the US
• Use of effective tick control products
• Close inspection of your dog after time spent outdoors
• Prompt removal of any ticks from your dog

When removing ticks, it is best to wear gloves to prevent the saliva of infected ticks from infecting you through cuts/scratches on your skin. There are inexpensive tick removal tools, found at vet clinics, pet stores, and online, that can make tick removal safer and easier.

Your vet will discuss and make further recommendations as to which tick preventatives should work best.

Can people get Rocky Mountain Spotted Fever?

Unfortunately, people are also susceptible to becoming infected with Rocky Mountain Spotted Fever when bitten by an infected tick. People cannot get infected directly from their dog.

There is a risk for transmission of the disease to people if they come in contact with the feces or saliva from an infected tick when removing them from a dog. Also, documented cases exist of people becoming infected with RMSF after receiving blood transfusions from an infected person.

Dogs act as sentinels for contracting this disease. Infected dogs may increase the risk for people and other dogs in areas where transmission is mainly due to the brown dog tick.

Any person or animal that is exposed to infected ticks is at risk of becoming infected with Rocky Mountain Spotted Fever. However, of the species that can become infected with RMSF, clinical signs of disease are only noted in dogs and people.

Read more:

Tick Talk - Dogs and Tick Control

Common Skin Diseases in Dogs

Flea and Tick Medication Guide for Pet Parents

Need to speak with a veterinarian regarding your dog’s Rocky Mountain Spotted Fever or another condition?

Click here to schedule a video consult to speak to one of our vets. You can also download the FirstVet app from the Apple App Store and Google Play Stores.