Rocky Mountain Spotted Fever in Dogs

Summary

Rocky Mountain Spotted Fever (RMSF) is a rare disease caused by a type of bacteria transmitted in the saliva of some species of ticks. This tick-borne bacteria causes potentially fatal disease in both dogs and people, emphasizing the importance of routine tick prevention for all dogs. 

In dogs, symptoms such as fever, joint pain, and lethargy arise within 3-14 days after receiving a bite from an infected tick. The diagnosis of RMSF is confirmed using a blood test. Treatment primarily involves long-term antibiotics. 1-10% of canine cases or RMSF are fatal, even when treated appropriately.

Humans living in the same household as a dog diagnosed with RMSF should consult a physician. Generally speaking, humans are exposed to the same types of ticks as their dogs, so a human living with a dog that tests positive for RMSF may have also been exposed. 

Due to the severity of RMSF and the risk of transmission across different species (including humans), it is advised that all dogs remain on a vet-recommended tick preventative year round. These medications reduce the dog’s exposure to ticks and help prevent them from introducing ticks into the home.

Risk Factors

RMSF is very rare. Dogs in endemic areas are at some risk of becoming infected. RMSF is most prevalent in the south Atlantic and south-central United States. Outdoor and rural dogs are at the highest risk of exposure. Approximately 1-3% of ticks in endemic areas test positive for the bacteria associated with the disease. RMSF is a very rare disease of no concern to pet parents outside of endemic areas. 

Dogs with fever, lethargy, joint and muscle pain, tremors, and vomiting require veterinary care as soon as possible. Approximately 1-10% of dogs diagnosed with RMSF die despite treatment. 

If a dog is diagnosed with RMSF, people exposed to similar environments as the dog are advised to consult with their physician. Approximately 250 to 1200 human cases of RMSF are reported each year.

Possible Causes

R. rickettsii  is the bacteria that causes RMSF and is primarily transmitted by the American dog tick, the Rocky Mountain wood tick, and the brown dog tick. Ticks feed on an infected host, then transfer the bacteria while feeding on a new host. Body fluids from ticks can also transmit disease. It is estimated that it takes 5-20 hours of tick attachment for the bacteria to transmit to a host.

Main Symptoms

Dogs develop symptoms of RMSF within 3-14 days of an infected tick bite. Early symptoms include:

• Fever • Decreased appetite • Enlarged lymph nodes (lymphadenopathy) • Joint pain • Coughing

• Difficulty breathing (dyspnea) • Swelling of the face or paws

Detailed Characterization

Severe symptoms of RMSF are linked to bacterial damage to the cells lining blood vessels. Symptoms include:

• Pinpoint, red, hemorrhagic spots on the gums and membranes around or in the eyes • Prolonged bleeding

• Bruising on the abdomen or legs

In some cases, RMSF leads to swelling of the brain, causing symptoms such as:

• Tremors • Seizures • Sensitivity to sounds, light and touch

All of these severe symptoms require immediate veterinary attention.

Testing and Diagnosis

Diagnosis is confirmed via blood test. General blood work is usually recommended to inform treatment as well as specific testing to confirm RMSF.

Steps to Recovery

RMSF is treated using antibiotics. In some cases steroids are also indicated. Most dogs diagnosed early in the course of the disease respond rapidly to treatment, with energy and appetite returning within days. Completion of the full antibiotic protocol is required, even if the dog is feeling better. 

Dogs that recover from RMSF are considered immune to future R. rickettsii infections.

Left untreated, RMSF increases in severity and ultimately becomes fatal. Cases with mild symptoms that have appropriate treatment delivered have a good prognosis. Dogs with severe symptoms have a poor prognosis, and about 1-10% of dogs die despite treatment.

Prevention

RMSF is not directly contagious from one dog to another or to other pets or people. Infection occurs by way of a bite from an infected tick.    

There is no vaccine available against R. rickettsii. The best method of prevention is to maintain all dogs on veterinarian-recommended year-round tick control products. Note: there are many parasite control products on the market that are neither effective nor safe. Always consult a vet when choosing external parasite control.

Is Rocky Mountain Spotted Fever Common in Dogs?

Rocky Mountain Spotted Fever is rare in dogs, even in endemic areas.

Typical Treatment

RMSF is typically treated with antibiotics. In some cases, steroids are also indicated.