Rickettsial Infection in Dogs

Rickettsial infections are caused by bacteria from the Rickettsia genus, which are often carried by arthropods such as ticks and fleas. There are several different types of the infection, with two more commonly seen in dogs. The infection may be treated with antibiotics, but the treatment needs to begin as soon as possible, which is why an early, correct diagnosis is important for a better outcome.

Symptoms of an infection with R. rickettsii include:

• Fever
• Anorexia
• Coughing
• Depression
• Abdominal pain
• Vomiting
• Diarrhea
• Enlarged lymph nodes

Depending on the stage, type, and severity of the infection, additional clinical signs may be present, including bleeding and swelling of the legs with ehrlichiosis and neurological signs with Rocky Mountain spotted fever.

Types

Ehrlichiosis affected a significant number of military dogs in Vietnam during the 1970s and is now endemic in the southern United States. The disease may be acute, subacute, and/or chronic, depending on the length of infection.

Rocky Mountain spotted fever is more prevalent in the southeastern and mid-Atlantic regions of the United States. This infection tends to be more common in younger dogs, especially those that spend a large portion of their time outdoors.

Rickettsia bacteria are spread to canines by ticks, specifically the brown dog tick, the American dog tick, and the Rocky Mountain wood tick, with several other species implicated depending on the country of residence. When a tick feeds on a dog, the bite may be contaminated by the arthropod's saliva, which leads to a bacterial infection. Rocky Mountain spotted fever has historically appeared to be more prevalent in German Shepherd dogs.

If your dog shows unusual clinical signs, bring him into the veterinarian for an initial examination. The veterinarian will take your dog's history and may perform laboratory testing, such as blood work or a urinalysis, both to narrow down possible causes for your dog's symptoms and to gauge his overall health.

Both ehrlichiosis and Rocky Mountain spotted fever are difficult to diagnosis, particularly in the early stages of the infection. The former is typically confirmed when antibodies are detected in the blood, which only occurs several weeks following exposure. The organism itself may be observed during the acute stage, but this is rare. If ehrlichiosis is suspected, the veterinarian may use a polymerase chain reaction to test for bacterial DNA.

Rocky Mountain spotted fever mimics other infections in terms of clinical signs and presentation, which makes it easy to misdiagnosis. The infection can be confirmed with direct immunofluorescent testing for antigen in tissues or with serologic testing for a rising immune response as the infection progresses.

A rickettsial infection can be treated with antibiotics. Tetracycline or Doxycycline is the antibiotic of choice for ehrlichiosis, and Rocky Mountain spotted fever though treatment needs to begin as early and swiftly as possible for a better response and may need to be continued through several weeks.

If necessary, supportive care will be provided while the infection runs its course. The veterinarian may recommend hospitalizing your dog while fluids are administered to prevent hydration or, if your dog is anemic, while a blood transfusion is performed. The prognosis is good for dogs that are treated early on, but if the disease progresses to the chronic stage, the chances of a full recovery become lower.

As with any treatment at home, it's imperative to provide your loved one with a safe, quiet, and covered place to rest in as he recovers, as well as access to plenty of fresh water. Depending on your dog's symptoms, you may wish to restrict his physical activity, though many dogs begin to recover quickly after treatment is started. Monitor your dog for additional clinical signs, and if you observe any behavior that is out of the ordinary, let your veterinarian know immediately.