Do not wait for lab confirmation. Start treatment immediately.
Across eastern Canada, a quiet ecological shift is unfolding as blacklegged ticks extend their range and carry with them a bacterial illness most physicians have rarely had cause to consider. Anaplasmosis, once a rarity in Canadian hospitals, has doubled in prevalence among tested ticks between 2022 and 2024, prompting doctors to rethink how they approach unexplained fevers in patients who may never have noticed a bite. The illness is treatable — swiftly and effectively — but only if the physician thinks to look for it before the window closes.
- Anaplasmosis cases are rising fast enough that an internal medicine physician in Toronto felt compelled to publish a case study as a warning to colleagues who may not yet have encountered the disease.
- The illness mimics the flu so convincingly — fever, fatigue, headache, no rash — that it can slip past even attentive clinicians, and patients often have no memory of a tick bite to offer as a clue.
- Untreated, the infection can escalate from vague malaise to heart inflammation, brain swelling, respiratory failure, or kidney damage, making diagnostic delay genuinely dangerous.
- Physicians are now being urged to prescribe doxycycline immediately when anaplasmosis is clinically plausible, rather than waiting for laboratory confirmation that may arrive too late to prevent serious harm.
- Public health officials are asking Canadians to photograph and submit ticks to eTick.ca, turning ordinary encounters with insects into data points that map a shifting disease landscape in real time.
A patient arrived at a Toronto hospital with fever and vague malaise — symptoms that could belong to almost any infection. Acting on clinical instinct, the treating team prescribed doxycycline before a diagnosis was confirmed. It was the right call: lab results later identified anaplasmosis, a bacterial illness spread by blacklegged ticks. The patient recovered fully, but the case left a deep enough impression on Dr. Michael Quon that he published it as a warning to colleagues across the country.
Anaplasmosis is not new to medicine, but it is newly common in Canada. Five years ago, Quon rarely saw it. Now it appears regularly, tracking the northward and eastward spread of blacklegged ticks through Ontario, Quebec, and Nova Scotia. Among ticks tested in 2024, six percent carried the responsible bacterium — double the rate recorded just two years earlier.
The clinical challenge is that anaplasmosis disguises itself. Its early symptoms — fever, exhaustion, headache, digestive upset — fit dozens of other illnesses, and many patients cannot recall being bitten. Without a rash to flag it the way Lyme disease sometimes does, the diagnosis depends on a physician thinking to look. If they do not, the consequences can be severe: myocarditis, brain inflammation, acute respiratory distress, kidney failure. A low blood cell count can offer a diagnostic clue, though co-infection with Lyme disease is possible and complicates the picture.
Quon's guidance to fellow physicians is unambiguous: do not wait for lab confirmation. If a patient presents with unexplained fever in a tick-endemic region, start doxycycline. The drug treats both anaplasmosis and Lyme disease, and the risk of waiting outweighs the risk of acting.
None of this is a reason to avoid the outdoors. Doctors are clear that the diseases remain relatively rare and that the benefits of outdoor activity are real. Prevention is straightforward: use DEET or Icaridin repellent, check for ticks daily, inspect children carefully after time outside. A tick must remain attached for more than twenty-four hours to transmit Lyme disease, and early removal dramatically reduces risk for anaplasmosis as well. When a tick is found, remove it with fine-point tweezers, clean the area, and consider submitting a photograph to eTick.ca — a small contribution to the national effort to understand where these insects are spreading and what they carry.
A patient arrived at a Toronto hospital with fever and general malaise—the kind of vague symptoms that could point to any number of infections. The doctors, working without a confirmed diagnosis, prescribed doxycycline to cover their bases. It was the right call. Lab work later confirmed what the antibiotic had already begun to treat: anaplasmosis, a bacterial infection transmitted by blacklegged ticks, the same insects that carry Lyme disease. The patient recovered fully. But the case stuck with Dr. Michael Quon, an internal medicine physician, enough that he decided to publish it as a cautionary tale for his colleagues.
Anaplasmosis is not new to medicine, but it is new to Canada—or at least, it is newly common here. Five years ago, Quon said, he did not see it in his hospital. Now he sees it regularly. The reason is straightforward: blacklegged ticks, which range in size from a poppy seed to a sesame seed, are spreading across the country from Manitoba eastward, with particular concentration in Ontario, Quebec, and Nova Scotia. Where the ticks go, the diseases they carry follow. Among ticks collected and tested in 2024, six percent carried Anaplasma phagocytophilum, the bacterium responsible for anaplasmosis. In 2022, that figure was three percent. The prevalence has doubled in two years.
The problem, from a clinical standpoint, is that anaplasmosis wears a disguise. Its early symptoms—fever, exhaustion, headache, digestive upset—are generic enough to fit dozens of other illnesses. A patient might not remember being bitten by a tick, or might not have noticed the bite at all. Between fifty and seventy-five percent of people diagnosed with early Lyme disease cannot recall the tick exposure that infected them; the same blind spot likely applies to anaplasmosis. This is where the disease becomes dangerous. If a doctor does not think to look for it, treatment gets delayed. And delay matters. Left untreated, anaplasmosis can progress to myocarditis, inflammation of the brain, acute respiratory distress, or kidney failure.
Quon's message to physicians is direct: do not wait for lab confirmation. If anaplasmosis is clinically possible—if a patient presents with unexplained fever in a region where blacklegged ticks are established—start doxycycline immediately. It is the first-line treatment for both anaplasmosis and Lyme disease, and it works. The risk of disease progression is significant enough to justify treating before the lab results come back.
Distinguishing anaplasmosis from Lyme disease is possible, though not always straightforward. Lyme disease often announces itself with an expanding rash in its early stages; anaplasmosis typically does not. Anaplasmosis patients frequently show a low blood cell count, a clue that can help narrow the diagnosis. But a person can be infected with both illnesses simultaneously, which complicates the picture further. Jules Koffi, a senior epidemiologist with the Public Health Agency of Canada, emphasized that physicians need to consider both possibilities when evaluating patients in high-risk regions.
None of this should send people indoors for the summer. Doctors are explicit on this point: the diseases remain relatively rare, and outdoor activity carries enormous health benefits. What matters is prevention through simple, unglamorous measures. Wear insect repellent containing DEET or Icaridin. Check yourself for ticks daily—and check thoroughly, including areas where ticks like to hide. Give children a daily bath and inspect them carefully. The window for transmission is narrow: a tick needs to remain attached for more than twenty-four to thirty-six hours to transmit Lyme disease, and while the timeline for anaplasmosis is not yet precisely known, removing a tick within a day makes infection probability very small.
When you find a tick, the Public Health Agency recommends using fine-point tweezers to grasp it as close to the skin as possible and pull straight out without twisting. Wash the area with soap and water or alcohol-based sanitizer. Then, if you want to contribute to national surveillance efforts, photograph the tick and submit it to eTick.ca for identification. The data helps track where these insects are spreading and how the risk landscape is changing. It is a small act, but in the context of a disease that is doubling in prevalence, small acts of awareness add up.
Citas Notables
This is not an infection that we encountered even five years ago in the hospital.— Dr. Michael Quon, internal medicine physician
A tick has to be on you for more than 24 to 36 hours to get Lyme disease. For anaplasmosis, the probability of infection is likely very, very, very small if removed within a day.— Dr. Jeffrey Pernica, infectious diseases specialist at McMaster Children's Hospital
La Conversación del Hearth Otra perspectiva de la historia
Why is anaplasmosis suddenly showing up on doctors' radar now, when the tick has presumably been here for years?
The tick has been here, but not in these numbers. The blacklegged tick population is expanding northward and eastward as climate patterns shift. More ticks means more opportunity for transmission. Doctors are seeing cases now that they simply didn't encounter five years ago.
So it's not that the disease is new—it's that it's arriving in places where doctors have no experience with it.
Exactly. A physician in Toronto in 2020 might never have thought to test for anaplasmosis because it wasn't part of their clinical landscape. Now it is. That's the real danger: the disease is treatable, but only if someone thinks to look for it.
The article mentions that half of Lyme disease patients don't remember their tick bite. How do you diagnose something when the patient has no memory of exposure?
You ask about outdoor activity, but you also accept that the absence of a remembered bite doesn't rule anything out. You look at the symptom pattern—fever, fatigue, low blood cell count—and you consider the geography. If someone lives in Ontario and has unexplained fever, anaplasmosis belongs on the differential diagnosis list now.
What's the practical difference between waiting for a lab result and starting treatment immediately?
The difference is disease progression. If you wait and the lab takes days to come back, the infection has more time to move from a treatable stage to a dangerous one. Myocarditis, brain inflammation, kidney failure—these are serious. The antibiotic works, so why not start it?
But doesn't that risk overtreatment? Giving antibiotics to people who might not have anaplasmosis?
Doxycycline is already the standard treatment for Lyme disease in these regions. If you're treating for one, you're covering for the other. The risk of withholding treatment outweighs the risk of treating empirically when the clinical picture fits.
What should someone actually do differently this summer?
The same things you should always do: use repellent, check yourself daily, remove ticks promptly. The difference is knowing why it matters now. These aren't abstract precautions anymore—they're the barrier between a treatable infection and a serious one.