Dog: Rocky Mountain Spotted Fever

General information

Other common/scientific names: Rickettsia rickettsii, RMSF

The tick population in the United States is exploding due to changing climate (less harsh winters), suburbanization and the increase in the deer population . Because of this, ticks are moving into new areas and bringing new diseases. As a result, tick-borne diseases in dogs are increasing. These diseases include anaplasmosis, babesiosis, ehrlichiosis, borreliosis (Lyme disease) and Rocky Mountain spotted fever. These diseases are typically infections of the blood. Because these infections are transmitted by a tick bite, a dog may be infected with more than one of these organisms at the same time.


Rocky Mountain spotted fever (RMSF) in dogs is caused by the bacteria Rickettsia rickettsii. The Rickettsia bacteria damage the cells which line the small arteries and veins in the dog’s body. This damage results in inflammation, causing these blood vessels to leak both fluid and blood into surrounding tissue. Depending on the severity of infection, various clinical signs result from this damage.


Dogs acquire RMSF by being bit by a tick carrying the bacteria. The American dog tick (Dermacentor variabilis) transmits the Rickettsia bacteria. Rocky Mountain spotted fever is most prevalent in the western and southwestern United States.

Cardinal symptom



Any organ system can be affected and clinical signs can be mild or severe enough to result in death. These signs include fever, lethargy, loss of appetite, lameness and enlarged lymph nodes. In more severe cases abnormal bleeding, coughing, abdominal pain, swelling of the face and limbs, vomiting and diarrhea can result.


Diagnosis of Rocky Mountain spotted fever should be made based on the presence of clinical signs and positive blood tests. Blood tests to determine a dog’s antibody levels to RMSF can aid in the diagnosis. Without clinical signs, a positive antibody test only indicates past exposure to the bacteria not an active infection. A second antibody test can be performed 10-14 days after the initial test. An active infection will show an increase in the antibody level. A complete blood count (CBC) may reveal low numbers of platelets. Other tests can be sent to a laboratory to detect the Rickettsia DNA in the blood.


Rocky Mountain spotted fever is treated with antibiotics. Treatment should be instigated based on clinical suspicion. Delaying treatment while waiting on blood results can result in the death of a dog infected with RMSF.


Dogs which are treated promptly have a good prognosis for recovery.


Dogs which go outdoors in wooded, tick infested areas should have some form of tick protection such as:

Because of the warmer winters, tick protection is recommended year around.

While the topical spot-on medications are the best defense in preventing tick-borne diseases, checking your dog for ticks after walking or playing in a wooded area is recommended since it takes several hours for an attached tick to transmit disease. This is especially important if you live in a tick infested area.


When applying the topical, spot-on medications, be sure to part the hair and apply the medication directly to the skin. Do not bath or allow your dog to swim for 2 days after application. The product may need to be re-applied more often than every 30 days.

Update version: 4/24/2014, © Copyright by
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