Rocky Mountain spotted fever (RMSF) is a bacterial disease caused by tiny, rod-shaped microorganisms called Rickettsia rickettsii ( R. rickettsii ), which are carried parasitically by the Dermacentor and Rhipicephalus species of ticks — common name include Rocky Mountain wood tick, American dog tick, and the brown dog tick. These ticks are widely distributed east of the Rocky Mountains in most of the contiguous United States with North Carolina, Oklahoma, Arkansas, Tennessee, and Missouri reporting over 60 percent of the RMSF cases.
Although first recognized in the Rocky Mountains, only a small percentage of RMSF cases are now found there. Since 2008, the incidence of the disease has increased while cases resulting in death have declined to less than 0.5 percent.
RMSF is the most commonly known of a group of diseases known as Rickettsia. Injected into dogs and people by feeding ticks, RMSF is a zoonosis which means it can be transmitted from animals to humans, however, direct transmission of organisms is not known to be passed from dogs to people. The R. rickettsii bacterium behaves like viruses, reproducing only inside living cells. RMSF, along with other serious tick-borne diseases such as Lyme, Ehrlichia, anaplasmosis, tularemia, and Babesia are good reasons to be extra vigilant in the great outdoors from March through October.
How Rocky Mountain spotted fever affects dogs.
RMSF organisms attack tiny blood vessels in the dog causing damage, inflammation, and the bruised or purplish "spots" which the disease is named for. These small pockets of hemorrhage may be visible on the skin, but they also occur in internal organs such as the heart, brain, and kidney which makes RMSF a potentially life-threatening, fatal illness.
Certain purebred dogs, especially German shepherds, are more likely to have a severe reaction to the R. rickettsii organism than other dogs.
Symptoms of Rocky Mountain spotted fever in dogs.
Unlike some other tick-borne diseases such as Lyme where the tick needs to be feeding for 24-48 hours before transmission occurs, in RMSF, transmission takes only 5-20 hours after the tick attaches. RMSF's incubation period from infection to onset of illness is from a few days to two weeks. Consequently, clinical signs in your dog may not occur in concurrence with the presence of a tick on the dog. Thus, the connection between the illness and the tick bite may not be made immediately.
RELATED: Removal Of Embedded Ticks In Dogs
Like many bacterial diseases, some of the clinical signs or symptoms are vague and non-specific in dogs and people, and other diseases must be ruled out before a diagnosis of RMSF can be confirmed.
Some of the symptoms of Rocky Mountain spotted fever are:
- Spots or rash.
- Fever usually occurs within five days of onset.
- Lack of appetite.
- Muscle and joint pain.
- Abdominal pain.
- Edema or fluid retention in the legs and face.
- Arrhythmia (irregular heartbeat)
- Sudden bleeding from the nose.
- Inflammation, conjunctivitis, and bleeding from mucous membranes, often the eyes.
- Ataxia or loss of coordination.
- Blood in the urine.
Diagnosis of Rocky Mountain spotted fever.
Due to the non-specific clinical symptoms, many other conditions, disorders and/or diseases must be ruled out by your veterinarian before they can make a definite diagnosis. Your dog's history will be reviewed, and your observations of the extent and duration of any clinical signs will be part of the diagnostic evaluation. Not every patient will present with visible signs such as spots, and if they do develop a rash, it may be a few days after they are already clinically ill.
Polymerase chain reaction (PCR) testing, which reveals RMSF DNA in the dog's blood, is the only definitive method used to diagnose RMSF. Serology may also be performed to detect a rising immune response over time. Conclusive results are often not available until well into the disease's progression.
Treatment of Rocky Mountain spotted fever.
Timing is crucial since the antibiotic doxycycline used to treat RMSF is most effective when started before the fifth day of symptoms. It's imperative to seek treatment immediately as any delay will have a negative impact on your dog's prognosis. Typically, to be on the safe side, your veterinarian will start treatment based on clinical symptoms, location, and risk of exposure with or without any known tick bites.
Recovery from Rocky Mountain spotted fever.
Provided you have taken prompt action and seek treatment for your dog within the first couple of hours after a tick bite, prognosis is usually good.
What you should know about ticks and prevention of RMSF.
From controlling ticks around the home with meticulous grounds maintenance and keeping your dog protected with tick control medication, prevention is simple and effective if practiced consistently. Most importantly, always check your dog for ticks thoroughly after being outside on your own property. If walking through a park or forested area or while camping, keep your dog on-leash and do a head-to-toe inspection regularly.
Quick removal of ticks is paramount for a positive outcome. Use caution removing any ticks you find or take your dog to the vet to have the ticks removed. Keep in mind the rickettsial bacteria is transmissible through fluids, tissues, blood, or feces through cuts or sores on your skin. Always thoroughly check yourself for ticks as well, including your shoes, socks, clothing, and belongings where ticks can easily attach.
To keep your property as tick-free as possible:
- Trim dense brush and foliage.
- Keep your grass clipped short.
- Remove leaf litter, debris, garbage, and woodpiles.
- Exclude wildlife, such as deer who carry ticks, with secure fencing.
Tick control products, available through all veterinarians and online, are an affordable preventive for the diseases that ticks transmit including Rocky Mountain spotted fever. When choosing a tick control product, ensure it is registered for the United States market and approved by the EPA.
Maintain your dog year round on one of the leading brands of tick control medication:
- Seresto ™.
Always check with your veterinarian before changing your pet’s diet, medication, or physical activity routines. This information is not a substitute for a vet’s opinion.
- Pet Health Network: Rocky Mountain Spotted Fever (RMSF) in Dogs
- Pet Helath Network: Ticks 101
- Pet MD: Rocky Mountain Spotted Fever in Dogs
- Pet MD: 7 Signs of Rocky Mountain Spotted Fever in Dogs
- Companion Animal Parasite Council: Rocky Mounted Spotted Fever
- Dog: Flea and Tick Products Made for the USA