Human cases of Rocky Mountain spotted fever reported in Ontario

The Office of the Chief Medical Officer of Health is informing hospitals and primary care practitioners to become more aware of Rocky Mountain spotted fever, as human cases have recently been documented in Ontario.1 Single cases have also been reported in Quebec,2 and Saskatchewan.3Rocky Mountain spotted fever is a serious, potentially life-threatening tick-borne illness caused by the bacterium Rickettsia rickettsii. The American dog tick (Dermacentor variabilis) is a common tick species in Ontario and a known vector for R. rickettsii.1 Two human cases of Rocky Mountain spotted fever have recently been confirmed (by clinical presentation and lab evidence) in Ontario, with both individuals being exposed in Long Point, Ontario.1 In addition, several dogs with a history of travel to the Long Point area have been diagnosed with Rocky Mountain spotted fever this summer. Local tick surveillance in the Long Point area has identified R. rickettsii in American dog ticks.1Symptoms of Rocky Mountain spotted fever usually appear within two to 14 days after a tick bite. They may include fever, headache, rash, nausea, vomiting, muscle pain and abdominal pain. The rash typically starts as a maculopapular rash on the wrists, forearms and ankles, then spreads to the trunk and becomes petechial over time.1 It is important to note that the illness can progress rapidly and the characteristic rash may be absent or delayed.1 Late-stage manifestations include noncardiogenic pulmonary edema (acute respiratory distress syndrome), cerebral edema, acute renal failure, hyponatremia, shock and seizure.4Prompt recognition and treatment of Rocky Mountain spotted fever are critical to preventing severe outcomes. The diagnosis is primarily clinical. Treatment with doxycycline should not be delayed while awaiting laboratory confirmation.1 The U.S. Centers for Disease Control and Prevention recommends doxycycline as the first-line treatment for adults and children of all ages. The recommended dosage for suspected Rocky Mountain spotted fever is 100 mg every 12 hours for adults, and 2.2 mg/kg twice daily for children weighing < 45 kg. The minimum course of treatment is five to seven days. Patients should be treated with doxycycline for at least three days after the fever subsides and there is evidence of clinical improvement.5 Toronto Public Health recommends that healthcare providers maintain a high index of suspicion for Rocky Mountain spotted fever in patients presenting with compatible symptoms and recent travel or exposure history to Long Point, Ontario or surrounding areas, and/or a history of a tick bite.1 Rocky Mountain spotted fever is not currently designated as a Disease of Public Health Significance in Ontario. However, healthcare providers are strongly encouraged to report all cases to their local public health unit to support surveillance efforts and provide valuable information about the risk of transmission in Ontario.1Advise patients to reduce their exposure to ticks by:Not walking barelegged in tall grass, wooded areas or marshlands.Trying to stay in the centre of a cleared trail to avoid contact with overgrown grass, brush and leaf litter.Wearing long sleeves, pants and fully-closed boots or shoes when walking in grassy or wooded areas.Tucking pant legs into your socks.Conducting a “tick check” on yourself, your family and your pets after exposure to tick habitat.Wearing light-coloured clothing to make the ticks easier to find.Using insect repellents containing DEET (N,N-diethyl-meta-toluamide). They can also be sprayed onto clothing, especially pants and socks.6References:Murti M. NEW: Rocky Mountain spotted fever in Ontario. Toronto Public Health's Physician e-Newsletter; September 26, 2025.The Canadian Press. Quebec reports first case of tick-borne Rocky Mountain spotted fever. August 19, 2025. (accessed September 30, 2025).Kozroski A. Rare case of Rocky Mountain spotted fever confirmed in Sask. CBC News. September 03, 2025. (accessed September 30, 2025).Emergency Care BC. Rocky Mountain spotted fever – diagnosis and treatment. Last reviewed on December 29, 2022. (accessed September 26, 2025).US Centers for Disease Control and Prevention. Clinical care of Rocky Mountain spotted fever. Health care providers. March 6, 2025. (accessed September 30, 2025).Haldimand-Norfolk Health Unit. Rocky Mountain spotted fever. (accessed September 30, 2025).

Human cases of Rocky Mountain spotted fever reported in Ontario

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