Rocky Mountain spotted fever (RMSF) is one of several tick-borne diseases that affect dogs. Caused by a bacterium called Rickettsia rickettsii (R. rickettsii), which is transmitted through tick bites, RMSF can be dangerous to dogs. Knowing the risk factors, signs, diagnosis and treatment are all help in preventing your dog from getting RMSF and treating it appropriately if they do contract it. Here’s everything you need to know about RMSF in dogs.
Where is Rocky Mounted Spotted Fever Found?
If you live in North America and your dog comes in contact with ticks, there is a risk for Rocky Mountain spotted fever, but some dogs, depending on where they live, are at a higher risk. Four types of ticks carry R. rickettsii: the American dog tick, Rocky Mountain wood tick, Lonestar tick, and brown dog tick.
The American dog tick is the primary RMSF tick vector (an organism that can pass diseases to another organism), and ranges in location throughout the entire eastern half of the United States, plus most of California. The Rocky Mountain wood tick range covers the general Rocky Mountain region., and the Lonestar tick ranges throughout the eastern and southern United States, but it is most predominant in the southeast.
The brown dog tick can be found across the entire United States. Currently, only the brow dog ticks found in Arizona and surrounding regions have been confirmed to carry R. rickettsii. However, researchers are concerned that the disease will spread through the brown tick population, which would also make RMSF more common.
RMSF has been reported in all 48 states of the continental United States. Most cases occur in the southern Atlantic states, from Delaware down through Florida, and the south-central states from Arkansas to Texas. More than 60% of human cases come from North Carolina, Oklahoma, Arkansas, Tennessee, and Missouri. North Carolina and Oklahoma alone account for 35% of these cases. Cases have also been reported in the Pacific Northwest. Despite its name, fewer than 5% of cases come from the Rocky Mountain region. RMSF cases are reported year-round, but most human cases are diagnosed from April through September. However, in Arizona and New Mexico, cases regularly occur throughout the year.
Rocky Mounted Spotted Fever in Humans
RMSF most commonly affects people and dogs, but dogs can’t transmit RMSF directly to humans. But if a tick bites your dog and your dog becomes infected, there is a chance that a tick could also bite and infect you. When you remove an tick from your dog that carries RMSF, you can also become infected if the tick’s fluids come into contact with your eyes or any open wounds.
While brown dog ticks carrying RMSF usually prefer dog hosts over human hosts, “tropical lineage” brown dog ticks, which are brown dog ticks found across the entire southern U.S., can prefer human hosts to canine hosts when the temperature rises above 100 degrees Fahrenheit.
How Do Dogs Get Rocky Mountain Spotted Fever?
When a tick attaches itself to a dog or human, the bacteria R. rickettsii is injected into the bloodstream. However, the tick needs to be attached for 5 to 20 hours before the bacterium enters the bloodstream, so quick removal is important. Tick prevention is the best method to prevent infection, according to Dr. Claire Wiley, DVM, DACVIM, Executive Director of the AKC DNA Program. Dr. Wiley also has a background in researching tick-borne diseases.
Because products that kill ticks after they attach can take longer than 20 hours to be effective, a product that repels ticks and prevents bites is a better option. “A commonly used product on the market, fipronil, kills ticks after 24 hours of attachment and will not be effective at preventing infection,” Dr. Wiley warns. As tick products are constantly changing and improving, your veterinarian is the best source of information about what product would work best for your dog.
Even with protection, it is important to inspect your dog for ticks at least once a day, especially during your area’s tick season, is important in case some ticks have managed to attach. Prompt tick removal is your second line of defense against RMSF.
The good news is that only a tiny percentage of ticks actually carry R. rickettsii. The highest percentage, 5%, is found in brown dog ticks in some regions of Arizona. In other areas, only about 1% of American dog ticks carry the bacteria. However, RMSF can be deadly. It’s estimated that between 1% and 10% of dogs with Rocky Mountain spotted fever die from the disease.
Signs of Rocky Mountain Spotted Fever in Dogs
R. rickettsii can only live inside the cells that line the blood vessels, and causes the smaller blood vessels to become blocked, inflamed, and to leak. This causes problems all over the body, but especially in the organs that are contain these affected blood vessels. Unfortunately, most of the visible signs of infection are vague and not specific to RMSF. Because of this, RMSF is often suspected and diagnosed later than it should be.
The most prominent signs of RMSF include fever, lethargy, appetite loss, decreased red blood cells, decreased platelets, rash, and lesions in the eyes. Other signs may include tremors, swollen testes or scrotal edema, crusty eyes, clear nasal discharge, excessive salivation, and bloody stool. Coughing, vomiting, diarrhea, and abdominal pain may also occur. Here are some of the most noticeable signs to help you identify if your dog has RMSF.
Fever is a consistent finding across dogs with RMSF. A controlled study on RMSF showed that the earliest sign of infection in dogs is a body temperature above 102.2 degrees Fahrenheit (39.5 degrees Celsius). This increased body temperature occurs 3 to 7 days after the infected tick bites the dog. The fever can last from 3 to 9 days, but in young puppies can appear sooner and last longer. Following the fever’s peak, about 10 to 12 days after infection, your dog’s body temperature will slowly go down until it reaches normal levels. Body temperature may continue to fluctuate as long as the dog is infected, even during treatment.
Because R. rickettsii damages the blood vessels, they can become leaky, slowing down blood clotting. Dogs with RMSF may experience prolonged or unexplained bleeding, like nosebleeds or signs of blood in the urine or stool. Blood in your dog’s urine may look red or brown, while in their stool, it may be red or dark and tarry.
Leaky blood vessels and decreased clotting also cause bruising, sometimes for no obvious reason. The bruises in dogs are spontaneous and often cover very large areas.
A day or two after the fever appears, dogs with RMSF become lethargic. This continues even after the fever goes away. Joint pain may also occur 3 days post-infection. About a week after they are infected with RSMF, dogs may refuse food for at least a day or two, coinciding with the time they are most lethargic. Some dogs may also exhibit tremors of the head, limbs, and body that last for a few days.
Swelling is characterized by extra fluid in the tissue. It can affect various parts of the body, but most often you will see it affecting a dog’s extremities, like the lips, face, ears, or scrotum. Lymph nodes, which are part of the immune system, are also very often enlarged in cases of RMSF.
Tiny areas of blood leakage can appear as small red spots called petechiae. They are most evident on the gums, inner cheeks, inner ear flaps, inner eyelids, whites of the eyes, and mucosa, which is the moist lining of the genitals, but they can also be visible anywhere on the skin. Petechiae usually appear 60 to 100 days post-infection and mostly in severe cases.
How Is Rocky Mountain Spotted Fever Diagnosed in Dogs?
Most of these signs can point to many other sicknesses, so RMSF may not be considered at first. Your vet should consider RMSF as a possibility if your dog is exhibiting fever along with one or more other signs of RSMF, and if the dog resides in areas where RMSF is common. But even a fever can be missed, as it may come and go after the first two weeks. When discussing with your vet, mention any history of recent tick exposure.
Basic blood tests, such as a Complete Blood Count (CBD) and a Chemistry Profile can provide additional clues that may lead to a diagnosis. Starting five days post-RMSF infection, select blood tests will show decreased red blood cell volume and decreased platelet numbers. General white blood cell counts will also decrease, but a type of white blood cell called monocytes increases. Urinalysis can detect infected blood cells in the urine that may not be visible to the naked eye.
If RMSF is suspected, specialized testing for antibodies, called serology, can show positive results as early as 7 to 10 days post-infection. False positives can occur because of cross-reactions to other Rickettsia species. This when exposure to one species of Rickettsia creates signs similar to the signs created by exposure of another Rickettsia species. “False negatives can also occur if tested too early, so a follow-up serology is recommended 4-6 weeks after initial infection,” cautions Dr. Wiley.
“Your vet can also perform a polymerase chain reaction (PCR) test for the presence of R. rickettsii,” Dr. Wiley adds, “but it may give a false negative. When conducting PCR and antibody tests, your vet will typically need to send out blood for analysis. Most vets will order both PCR and serology.”
“Coinfection with other vector-borne diseases is also common,” Dr Wiley adds. “Your vet will likely run comprehensive PCR and serology tests for multiple vector-borne diseases.”
How to Treat Rocky Mountain Spotted Fever in Dogs
Because early treatment is vital, if RMSF is suspected treatment is usually started even before test results come back. Improvement is often dramatic enough to justify continued treatment, even without an official diagnosis.
The drug of choice for treating RMSF in dogs, is doxycycline, which is also used when humans have RMSF. A recommended treatment of doxycycline for goes about 10 to 21 days. Improvement is usually seen quickly, especially if the treatment begins early on in the disease. Most dogs recover completely with no relapses, as long as treatment is not stopped early.
Supportive care can also help dogs with RMSF treatment. They may need appetite stimulants, pain medication, and IV fluids to rehydrate them if they’ve been vomiting. To get the proper supportive care, your dog may have to be hospitalized for a few days.
Dogs that are simultaneously infected with other tick-borne diseases need to be treated for those as well. Some of these illnesses, such as Lyme disease, anaplasmosis, and ehrlichiosis also respond to doxycycline. But others, such as babesia and bartonella, do not. Dr, Wiley notes that those would need to be treated with another drug.
Fortunately, the prognosis is excellent for RMSF if treated early. “The primary concern is the risk of death without treatment,” says Dr. Wiley. If you suspect that your dog might have RMSF, consult your veterinarian as soon as you can for next steps.
Are There Long-Term Side Effects to Rocky Mountain Spotted Fever?
Typically, there are no long-term problems if the sickness is caught early enough. “The concern with long-term problems depends on how severe those acute conditions were and how effectively they heal,” Dr. Wiley says. She notes that severe RMSF cases can damage the kidneys, myocardium, which are the middle layer of the heart’s muscles, and central nervous system as a result of endothelial damage, which is when the lining of the blood vessels is impaired.
Once cured, is a dog then immune from RMSF? “I see mixed reports,” says Dr. Wiley. “Some [researchers] say that after infection protection is lifelong, whereas others say reinfection can occur.” She warns that owners should not to become complacent, regardless. “Even if a dog develops immunity to RMSF, tick prevention is still crucial, as ticks can also transmit other diseases.”
Given that at least short-term immunity is possible, it seems that a vaccine could be developed. But Wiley doesn’t think this is a good idea. “RMSF is deadly because of the response it triggers from the immune system, similar to Lyme disease,” she explains. “A vaccine triggers the immune system, so will a vaccine trigger an autoimmune condition?” This argument is already a concern with Lyme vaccines.
The most concerning effect of Lyme disease is immune-mediated glomerulonephritis—basically, a type of kidney failure that can also occur with RMSF. “These immune complexes developed in response to Lyme end up damaging the kidneys, and theoretically a vaccine may do the same.”
Preventing RMSF in Dogs
The best way to prevent RMSF is to prevent tick bites. Tick prevention is always advancing, so ask your veterinarian about any new developments. Also, ask your vet which method of tick prevention they think would be best for your dog. Dr. Wiley likes tick prevention collars that contain the ingredient flumethrin, but other tick repellents are constantly being investigated.
Keep your grass mowed short. If your dog walks near a wooded area, they risk the possibility of ticks attaching themselves. After walks, inspect your dog’s entire body for ticks, paying special attention to their ears, head, neck, groin, toes, and armpits. Check yourself, too!
Remove any ticks you find right away. Never remove ticks with your fingers. Instead, use fine-point tweezers or a tick removal hook, with a slow, pulling motion. Be sure you’ve removed the whole tick. After you’ve finished removing the tick, wash your hands thoroughly, clean the affected site with rubbing alcohol, and disinfect the tick removal tool.
Most of all, take note of any changes in your dog’s activity and appetite. Keep an eye out for nosebleeds or other signs of unusual bleeding. Take your dog’s temperature if you suspect any problems, and if something seems off with your dog’s behavior, don’t delay having your veterinarian check your dog, especially if they were recently bitten by a tick. When talking to your vet, bring up the possibility of RMSF, even if you’re not in an area known for it, especially if you’ve traveled through an area where RMSF is common.