Rocky Mountain Spotted Fever in Dogs: Symptoms and Treatment

Rocky Mountain Spotted Fever in dogs (RMSF) is a tick-borne disease caused by the bacteria Rickettsia rickettsii. The bacteria infect cells lining the blood vessels, causing inflammation that can affect multiple organs.

Early antibiotic treatment is crucial, as delaying treatment can worsen the disease and prognosis.

What Is Rocky Mountain Spotted Fever in Dogs?

Rocky Mountain Spotted Fever in dogs (RMSF) is a tick-borne disease caused by the bacteria Rickettsia rickettsii. Rickettsia is a specialized type of bacteria that can only live inside other cells.

Once the bacterium enters the bloodstream, it quickly enters and infects the cells lining the blood vessels (endothelial cells), causing inflammation (swelling) of those vessels and the organs they supply. 

RMSF can affect many species, but it most commonly affects dogs and humans.

History of Rocky Mountain Spotted Fever

RMSF was first discovered in 1896 in Snake River Valley, Idaho. It reportedly got its name from the trademark rash in humans, which consists of small red spots and blotches that begin on the wrists and ankles and spread up the arms and legs.

It is sometimes referred to in humans as “black measles” because, in the late stages of the disease, the skin turns black around the rash.

Where Is Rocky Mountain Spotted Fever Found?

RMSF has been reported in North, South, and Central America. Within the U.S., RMSF has been diagnosed in every state except Vermont and Alaska, but it is most common in North Carolina, Tennessee, Oklahoma, Arkansas, and Missouri.

RMSF is the most common rickettsial disease in dogs in the U.S. Correlating with tick season, RMSF is most often diagnosed from April to October. 

What Are the Symptoms of Rocky Mountain Spotted Fever in Dogs?

Symptoms of Rocky Mountain Spotted Fever in dogs are typically vague and nonspecific and usually appear two to 14 days after a tick bite. 

Common signs include fever, lethargy, loss of appetite or weight, muscle or joint pain, swollen joints, and lameness.

Other symptoms may include:

• Fever (up to 105 F)
• Lethargy
• Anorexia or weight loss
• Painful muscles or joints
• Swollen joints
• Lameness
• Enlarged lymph nodes
• Peripheral edema (swollen legs)
• Red spots (petechiae) or bruising (ecchymosis) on the skin or mucous membranes
• Coughing
• Vomiting or diarrhea

What Causes Rocky Mountain Spotted Fever in Dogs?

Rocky Mountain Spotted Fever in dogs is caused by infection with Rickettsia rickettsii and is most often spread through tick bites. 

Ticks associated with transmission include the Rocky Mountain wood tick (Dermacentor andersoni), American dog tick (Dermacentor variabilis), and brown dog tick (Rhipicephalus sanguineus).

Dogs cannot transmit RMSF directly to each other or to humans. Transmission can occur through a tick bite, typically requiring five to 20 hours of attachment, ingestion of an infected tick, or direct contamination of a wound by tick feces.

How Is Rocky Mountain Spotted Fever in Dogs Diagnosed?

Veterinarians may diagnose Rocky Mountain Spotted Fever in dogs using a physical exam, blood and urine testing, antibody titers, and polymerase chain reaction (PCR) testing.

Physical Exam and History

Your veterinarian will conduct a physical exam to determine whether your dog has a fever, joint swelling, or enlarged lymph nodes.

If you've recently traveled with your dog or your dog has had recent tick exposure, it's important to share that information with your veterinarian.

Blood and Urine Testing

A complete blood count (CBC), serum blood chemistry, and urinalysis will likely be recommended for a baseline evaluation.

Antibody Titers and PCR Testing

If your veterinarian suspects RMSF or another tick-borne illness, specialized laboratory testing may be recommended.

This may include antibody titers, which test for an immune response (antibodies) to the presence of the bacteria Rickettsia rickettsii.

Another option is polymerase chain reaction (PCR) testing for the presence of Rickettsia rickettsii. PCR testing may be performed as part of a tick PCR panel for multiple tick-borne diseases.

How Is Rocky Mountain Spotted Fever in Dogs Treated?

Rocky Mountain Spotted Fever in dogs is treated with antibiotics, and early treatment is crucial for successful RMSF management.

Doxycycline is frequently used, but your veterinarian will determine the best antibiotic for your dog.

Your veterinarian will likely start antibiotics immediately before confirmatory test results are available, as any delay in treatment can worsen the disease and prognosis

Depending on the severity of the disease, your dog may need to be hospitalized for IV fluids to correct dehydration and supportive care such as appetite stimulants or pain medications.

Recovery and Management of Rocky Mountain Spotted Fever in Dogs

Most dogs with Rocky Mountain Spotted Fever recover and do well with early antibiotic therapy and supportive care. However, RMSF can be deadly if treatment is delayed, with an estimated 1–10% of infected dogs having a fatal infection.

Hospitalization and Recovery

Some dogs may be managed on an outpatient basis, but many will require hospitalization. Hospitalization typically includes two to three days of IV fluids, supportive care, and antibiotics.

Dogs can usually be discharged once their fever breaks and they are consistently eating and drinking on their own.

Other Dogs in the Household

RMSF cannot be spread from dog to dog. However, if multiple dogs were exposed to the same area of ticks, consult your veterinarian about testing and/or treating all dogs in your household.

Human Exposure to RMSF

RMSF is not zoonotic, meaning you cannot get it directly from your dog. However, humans can get RMSF from a tick bite or from tick feces or bodily fluids when removing a tick.

If you think you have been exposed to RMSF, seek medical attention immediately.

How To Prevent Rocky Mountain Spotted Fever in Dogs

The best way to help prevent Rocky Mountain Spotted Fever in dogs is to protect your dog from ticks with monthly flea and tick prevention and limit exposure to areas where ticks commonly live. There is no vaccine for RMSF.

Topical and oral flea and tick prevention options are available, so discuss the best option for your dog with your veterinarian. It is also ideal to keep your dog out of thick brush or wooded areas where ticks commonly live.

Check Your Dog for Ticks

Inspect your dog for ticks after outdoor time, especially from April through October, when ticks are more prevalent. Early removal of ticks helps decrease the likelihood of transmitting the disease.

Wear latex gloves when removing ticks and be sure to remove the entire head/mouthparts. You can use tick removal tools to help with this process or ask your veterinarian or a veterinary technician for help removing ticks.