Rocky Mountain Spotted Fever in Dogs

Causes, Treatment, and Prevention

Dermacentor variablis (American dog tick)

Smith Collection/Gado / Contributor / Getty Images

Rocky Mountain spotted fever (RMSF), a bacterial disease transmitted by ticks, can affect dogs of all ages and breeds throughout the United States. The symptoms of RMSF vary and range from mild lethargy to extreme joint pain, swelling, and seizures. Early antibiotic treatment is often effective, but preventing ticks from biting dogs is the best defense against this infection.

What Is Rocky Mountain Spotted Fever?

Rocky Mountain spotted fever is a systemic infection caused by Rickettsia rickettsii bacteria. These bacteria are carried by ticks and passed to dogs via the bite of an infected tick. When a tick feeds, the bacteria in its saliva travels to the bloodstream and reproduces in the cells of the blood vessels, which become inflamed and constricted.

Symptoms of Rocky Mountain Spotted Fever in Dogs

Rocky Mountain spotted fever can be difficult to diagnose solely on symptoms because of the wide variation of signs and similarity to other illnesses. Initial signs of R. rickettsii infection may include:

Symptoms

  • Fever
  • Lethargy
  • Swollen lymph nodes
  • Coughing
  • Muscle and/or joint pain
  • Abdominal pain
  • Vomiting and/or diarrhea
  • Swelling of the face or limbs
  • Petechiae (red spots) on the gums or eyes
  • Seizures

An increase in body temperature, coughing, swollen lymph nodes, and abdominal distress are generalized symptoms of RMSF. Dogs with this tick-borne illness are also likely to experience muscle pain, lethargy, and swollen legs.

As the infection progresses, swelling of the face and legs is common, and a dog may develop small hemorrhages or bruises called petechiae that appear as red spots inside the mouth and on the whites of the eyes.

Causes of Rocky Mountain Spotted Fever

Rocky Mountain spotted fever is a rickettsiosis or intracellular bacterial infection caused by the bacteria Rickettsia rickettsii. It is spread through the bites of several different kinds of ticks, including:

  • American dog tick (Dermacentor variablis)
  • Rocky Mountain wood tick (Dermacentor andersoni)
  • Brown dog tick (Rhipicephalus sanguineus)

Diagnosing Rocky Mountain Spotted Fever in Dogs

A full physical examination is performed by a veterinarian after symptoms of RMSF are exhibited. If RMSF is suspected, blood work and potentially a urinalysis and X-rays will be recommended.

Blood tests will check levels of white blood cells, which will often be low in infected dogs. A special two-part test called an Indirect Immunofluorescent Assay (IFA) may also be performed to look for antibodies to the R. rickettsii bacteria.

If a dog has Rocky Mountain spotted fever, the complete blood count (CBC) may also show abnormal protein levels along with abnormal electrolyte, liver, or kidney values.

Treatment

Since Rocky Mountain spotted fever is caused by bacteria, antibiotics are used to treat it. Typically, a three-week course of antibiotics is effective. In some cases, steroids may be needed as the infection can trigger an overactive immune response that will start to attack the dog's own body. In severe cases, a blood transfusion may be needed. If left untreated, Rocky Mountain spotted fever can be deadly.

Prognosis for Dogs with Rocky Mountain Spotted Fever

Dogs have the best chance of survival and recovery from RMSF if the infection is diagnosed and treated early in the course of the disease. Infections that have progressed are more challenging to treat because they affect more organs and can trigger autoimmune responses.

How to Prevent Rocky Mountain Spotted Fever

Ticks are the carriers of this disease, so prevention depends upon preventing tick bites. Owners should keep dogs away from tick-infested areas and use a tick preventative as recommended by their veterinarians.

Daily tick-checks and tick removal after being in wooded or un-mowed grassy areas will help reduce the chances of tick-borne illnesses being transmitted. If a tick is found on a dog, it should be removed as soon as possible to prevent transmission of the disease. The entire tick, including the head, will need to be carefully pulled out.

Article Sources
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  1. Rocky Mountain Spotted Fever in Dogs. Merck Veterinary Manual.

  2. Rocky Mountain Spotted Fever (Tick Fever) in Dogs. Merck Veterinary Manual.