Rocky Mountain spotted fever (RMSF) is a tickborne disease. It was first discovered in Native Americans, soldiers, and settlers in the Western United States in the 1890s. By the mid-1900s, the condition was the most common and severe human tickborne disease in the United States.
However, it was not until the 1970s, however, that veterinarians recognized this condition in dogs.
Ticks that spread this infection live throughout the country, making this condition a widespread threat.
Rocky Mountain spotted fever in dogs is a tick-borne bacterial infection that may cause a wide range of clinical signs. Some infected dogs remain completely asymptomatic, meaning they show no signs of the infection. Other dogs, however, may develop fatal multi-system organ failure.
Although many animal species can become infected with Rocky Mountain spotted fever, only dogs and humans develop clinical signs of disease.
Rocky Mountain spotted fever is not the same as Colorado Tick Fever (CTF), which is a viral tick-borne disease.
Humans cannot catch Rocky Mountain spotted fever directly from an infected dog. It cannot be passed from dog to dog or from dogs to other pets.
However, if your dog becomes infected, this indicates that Rocky Mountain spotted fever is present in your area and you are also at risk of contracting the infection.
Rocky Mountain spotted fever is a bacterial infection spread through tick bites, by passing the bacterium Rickettsia rickettsii .
Tick species that cause Rocky Mountain spotted fever in dogs include:
Ticks become infected with the bacteria after feeding on an infected animal (often a rabbit or rodent). Once infected, they transmit the infection to dogs or humans when feeding.
If a tick carrying Rocky Mountain spotted fever bites you or your dog, signs of illness typically develop within two weeks of the bite.
Rocky Mountain spotted fever is found throughout North America, Central America, and South America.
In the United States, the disease is most common in the Mid-Atlantic, Southeast, Midwest, and Western regions.
According to statistics from the Centers for Disease Control, over 60 percent of human cases of Rocky Mountain spotted fever in the United States come from just five states ( 1 ):
Cases of Rocky Mountain spotted fever occur year-round. Higher numbers of cases happen in the warmer months, from March through November, typically peaking in June and July. This seasonal variation follows increases and decreases in tick activity.
Symptoms of Rocky Mountain spotted fever in dogs may vary significantly, depending on the pet’s overall health, immune system, and how quickly veterinarians treat and diagnose the condition.
In the early stages of infection, dogs typically show vague signs of illness that cannot be directly linked to any specific cause. These signs may include fever, weakness, decreased appetite, generalized pain or discomfort, and vomiting.
As the disease progresses, more serious signs may be visible. Rocky Mountain spotted fever affects the walls of the blood vessels. Therefore, it causes a wide variety of signs, depending on the affected body part.
Signs of Rocky Mountain spotted fever in dogs are divided into several categories:
None of these symptoms are specific to Rocky Mountain spotted fever. Therefore, a veterinarian needs to perform diagnostic testing to determine the cause of a dog’s illness.
Rocky Mountain spotted fever is challenging to diagnose, because clinical signs are highly variable. Your veterinarian will likely perform multiple tests before arriving at a diagnosis.
The first step is a complete blood cell count (CBC) and serum biochemistry, which analyzes the clear pale yellow liquid within a dog’s blood called serum.
The serum biochemistry in a dog with Rocky Mountain spotted fever may be normal or abnormal, depending on the affected body systems. The CBC, however, often points towards the diagnosis of Rocky Mountain spotted fever.
Abnormalities in a dog’s CBC may include:
If your veterinarian suspects Rocky Mountain spotted fever, he or she will conduct further testing to confirm the diagnosis.
Rocky Mountain spotted fever has two specific tests:
Serology – This is a test that looks for antibodies that the body makes to fight Rocky Mountain spotted fever. These antibodies are present in the blood within 7-10 days of infection and persist for a long time. After an initial serology test, another one may be necessary 2-3 weeks later to see if there has been a significant rise in the antibody levels.
Polymerase chain reaction (PCR) testing – This test looks for the presence of actual bacteria within the body. The advantage of this test is that a single positive test is adequate to make a diagnosis of Rocky Mountain spotted fever in dogs. The disadvantage, however, is that this test is not very sensitive and may miss some cases.
Your veterinarian may suggest performing serology and PCR simultaneously, to increase the chances of obtaining an accurate diagnosis.
Rocky Mountain spotted fever is treated with antibiotics. Several different antibiotics treat this infection, although doxycycline is used most commonly.
In severe cases, additional therapies may be needed. Dogs may be hospitalized for intravenous fluids and injectable antibiotics if they are vomiting or severely dehydrated.
In some dogs, widespread inflammation associated with Rocky Mountain spotted fever veterinarians may use prednisone or other steroids.
Severely anemic dogs may require a blood transfusion.
In general, dogs improve quickly with treatment. Dogs often begin to feel better within as little as 24-48 hours and laboratory abnormalities typically resolve within two weeks.
If veterinarians catch and treat Rocky Mountain spotted fever early, the prognosis is excellent. Most dogs will have lifelong immunity after infection.
Prognosis is guarded if there is delayed treatment and a dog comes in critically ill.
The most common antibiotic used to treat Rocky Mountain spotted fever in dogs is doxycycline. Pet parents administer it orally, as a tablet or capsule, once or twice daily for 21 days.
Side effects include nausea and vomiting, although giving the medication with food can minimize these effects.
Alternative antibiotics (if doxycycline is unavailable) include
The costs of treating Rocky Mountain spotted fever vary, depending on the severity of illness, the dog’s size, regional price variations, and other factors.
In a dog diagnosed early in the course of disease, you can expect to pay the following:
If dogs require aggressive treatment, costs may be significantly higher. You may spend thousands of dollars for hospitalization, intravenous fluids, and other supportive care.
For this reason, it’s important to take your dog to the veterinarian promptly if you see signs of illness.
To prevent your dog from contracting Rocky Mountain spotted fever, use tick prevention year-round. Make sure you’re following dosing instructions according to the manufacturer’s recommendation.
Even dogs living in urban areas should receive regular tick prevention, because urban rodents and other wildlife can act as a host for ticks and Rocky Mountain spotted fever.
A number of effective tick preventions are available, including topical products and oral medications. Talk to your veterinarian to determine the best tick prevention for your dog.
You should also check your dog for ticks after spending time in the woods or other high-risk areas such as high grass.
Remove ticks by using tweezers to grasp the tick near your dog’s skin and firmly pull the tick out. Veterinarians do not typically recommend antibiotics for a single tick bite. Talk to your veterinarian if you are in a high-risk area.
