Rocky Mountain Spotted Fever
What do I need to know about Rocky Mountain Spotted Fever (RMSF) in Southern Ontario?
There’s a new tick-borne disease in our own backyard to worry about! We used to consider it as “exotic”, but now Rocky Mountain Spotted Fever is not just a disease of the mountains of western North America. This disease spread is associated with climate change allowing an expansion of the organism further east and north than its traditional geographic location. It has been found in ticks that live in Southern Ontario, and has caused illness in dogs here.
What is Rocky Mountain Spotted Fever??
–RMSF is a serious bacterial illness caused by Rickettsia rickettsii, spread through the bite of infected ticks—primarily the American dog tick (Dermacentor variabilis), with possible involvement of the brown dog tick (Rhipicephalus sanguineus). These ticks are both present in the Niagara Region.
Where is RMSF?
RMSF remains rare in Canada, but cases have been spotted in Southern Ontario—especially in areas like Long Point, where ticks are more of a problem. In July 2025, several dogs in that region were diagnosed with RMSF, including a fatal case. That same month, Quebec confirmed its first locally acquired case in a human
The Basics about RMSF
- Transmission & risk: Dogs become infected through tick bites, with symptoms typically appearing 2–14 days after exposure.
- Symptoms to watch for:
- Fever, poor appetite, lethargy
- Muscle/joint pain, swollen limbs
- Vomiting, diarrhea, coughing
- Facial or limb swelling, bleeding (nose/gums), neurological signs like wobbling or hypersensitivity. The name “Spotted” is due to small spots of bleeding sometimes seen in the skin as a result of the effect of the organism on blood clotting.
- Diagnosis: Vets may observe non-specific signs alongside a history of tick exposure. Blood tests may show low platelets, anemia, abnormal white blood cells, and organ abnormalities. The diagnosis is confirmed with blood samples sent to an external reference laboratory.
- Treatment & prognosis:
- Doxycycline is the treatment of choice (7–21 days depending on dose), often with rapid improvement.
- Supportive care may include IV fluids, hospitalization, and possibly additional treatments if complications arise (e.g., steroids, blood transfusions).
- Early treatment usually leads to a good prognosis, but delayed care can increase the risk of fatality or long-term issues.
- After recovery, dogs often develop long-lasting immunity.
- Zoonotic considerations: Dogs themselves do not directly transmit RMSF to humans—transmission occurs only via infected ticks—but dogs can introduce infected ticks into the human environment. The disease in people has similarities to that in animals.
Prevention & Practical Steps
Personal Protection
- Avoid tick-infested environments (wooded, grassy, brush areas).
- Use insect repellents (DEET or icaridin) and wear permethrin-treated clothing.
- Wear light-colored, protective clothing and tuck pants into socks.
- After outdoor activity, thoroughly check for ticks on yourself, children, and pets and remove promptly with fine tweezers or tick removal tools.
Protecting Pets
- Use year-round tick prevention (topical, oral, or long-acting products like collars) as recommended by a veterinarian.
- After outdoor outings, inspect pets for ticks—removing them quickly reduces risk of transmission. This is still important even with the use of tick prevention as RMSF can be transmitted rapidly from the attached tick to the host.
- If your pet shows any symptoms or had tick exposure—especially if in areas like Long Point—consult your vet promptly.
Awareness of Tick Range Expansion
- Be aware that climate change is expanding tick habitats across Ontario, increasing disease risk to people and pets.
- Dogs have been useful as early indicators of emerging RMSF, especially in new areas.
General Reminders
- Never delay treatment if RMSF is suspected—early doxycycline therapy significantly reduces severe outcomes.
- Public awareness and coordinated veterinary, medical, and public health efforts are crucial for emerging risks.