Tick-borne infections are becoming more common in Canada. Here we present the first reported case of anaplasmosis in southwestern Ontario in a 64-year-old woman who presented to the emergency department with a 1-week history of fever, fatigue, and progressive confusion. Clinical examination findings suggested meningoencephalitis, with decreased consciousness and generalized stiffness of neck range of motion noted. Despite extensive testing, the diagnosis remained elusive. To rule out tick-borne diseases, clinicians conducted additional laboratory tests and sent these to a laboratory in Manitoba, substantially delaying confirmation. Treated empirically with vancomycin and ceftriaxone, the patient showed no improvement after 4 days. Subsequently, based on clinical suspicion of a tick-borne disease, clinicians decided to treat with empiric doxycycline, resulting in rapid clinical improvement within 24 hours. Assay results later confirmed anaplasmosis, suggesting an unrecognized tick bite. Consequently, due to the preemptive empiric treatment decision, the patient recovered with complete resolution of symptoms. Although those treating the patient had seen cases of tick-borne diseases before, such as Lyme disease, there was initial diagnostic confusion because of the rarity of anaplasmosis in Ontario. With climate change contributing to increased exposure to tick-borne diseases such as anaplasmosis,1,2 and cases of once-rare tick-borne infections in Canada continuing to increase,3-7 primary care physicians must consider this possibility, especially in endemic areas.3-5

Therefore, we present this case to highlight the need for health care providers to maintain a high suspicion for anaplasmosis and other tick-borne diseases in patients presenting with unusual or severe infectious syndromes.8-12

In July 2024, a 64-year-old woman was admitted to Brantford General Hospital in Ontario with suspected meningoencephalitis following a 2-week trip to a cottage near Ottawa, Ont. While other family members reported tick bites, she did not.

The day before admission, the patient experienced headaches localized to the right temple and she became increasingly confused. She developed fever and balance issues and her family decided to seek urgent medical help. Upon admission, the patient was confused and disoriented to time, place, and person. Although she could answer some questions, the patient relied on her husband for support. She exhibited decreased consciousness but denied photophobia, phonophobia, sore throat, or coryza symptoms. A review of her systems and history had negative results for cough, dyspnea, rash, or extensive travel.

The patient presented with fever of more than 40°C and oxygen saturation level of 96%. Cardiac, respiratory, and abdominal assessment findings were unremarkable, with normal breath sounds (no adventitious sounds heard) and soft abdomen without organomegaly or skin rashes. Neurologically, the patient was alert but disoriented to time and place (Glasgow Coma Scale score=14), requiring her husband’s assistance for basic questions. Cranial nerves remained intact with equal and reactive pupils and preserved facial symmetry. Deep tendon reflexes were symmetrically brisk (3+) with flexor plantar responses bilaterally. Muscle strength was preserved (5 of 5) throughout, although mild right-sided coordination deficits were noted on finger-to-nose testing. Romberg sign was present and gait assessment revealed mild ataxia with impaired tandem walking. No focal deficits or aphasia were observed, although the patient demonstrated difficulty with rapid alternating movements. A notable finding was neck stiffness on flexion, suggesting meningoencephalitis.

The patient was initially treated intravenously with 1.25 g of vancomycin every 12 hours, 10 mg/kg of acyclovir every 8 hours, and 2 g of ceftriaxone every 12 hours for possible viral or bacterial meningoencephalitis pending cerebrospinal fluid (CSF) culture results (Table 1). The hospitalist team consulted the infectious diseases team for guidance on management of the patient. Anaplasma species serology and nucleic acid amplification testing assays were sent to the National Microbiology Laboratory site in Winnipeg, Man, for analysis,13 creating diagnostic and treatment delays. Four days after admission, the patient remained confused with no clinical improvement.

While awaiting CSF assay results, we initiated empiric doxycycline twice daily for 7 days, as per protocol for Lyme disease and other tick-borne infections.14 This intervention produced defervescence and substantial cognitive improvement, with the patient discharged 5 days after initiating doxycycline. At follow-up with the infectious diseases team 2 weeks later, she was in her usual state of health, except for some mild residual fatigue. Anaplasmosis was subsequently confirmed.

Laboratory and diagnostic timeline for 64-year-old woman with meningoencephalitis

Anaplasma phagocytophilum, a bacterium transmitted by black-legged ticks (Ixodes scapularis),3,5 is a public health concern in Canada.5,7,15-17 In eastern Ontario, black-legged Ixodes ticks transmit a number of diseases, including Lyme disease (caused by the Borrelia burgdorferi bacterium), with the prevalence of disease increasing yearly.3,7 Since 1988, the Ontario Agency for Health Protection and Promotion (commonly known as Public Health Ontario) has been reporting on Lyme disease, with a province-wide document of cases available from their website.7

On July 1, 2023, Public Health Ontario designated 3 additional tick-borne diseases as diseases of public health significance: babesiosis (Babesia microti and other Babesia species), Powassan virus infection (Powassan virus), and anaplasmosis (A phagocytophilum), reflecting their considerable rise in Ontario.16

Human granulocyte anaplasmosis (HGA) is caused by the bacterium A phagocytophilum15,17 and transmitted by the I scapularis tick.3,5 While the true incidence and prevalence of HGA remain unknown, climate change1,2 has expanded the tick vector’s geographic reach.3-7 HGA presents with nonspecific symptoms,8-12 including fever, fatigue, myalgia, headache, cough, and dyspnea.8-12,17,18 The spectrum of illness may include sepsis, renal failure, meningoencephalitis, and rhabdomyolysis.5 Neurologic manifestations of anaplasmosis are rare and hardly reported.8,11,19

Tick-borne diseases can present diagnostic challenges, often delaying accurate diagnosis and subsequent treatment.20 Delayed laboratory confirmation compounds these difficulties.13 While morulae on peripheral blood smears are highly suggestive of anaplasmosis or ehrlichiosis, they are rarely seen and not pathognomonic.21 As such, a polymerase chain reaction (PCR) or serology test is usually required,13 but results are not timely, necessitating empiric therapy.14

In our case, serology results were negative, highlighting another diagnostic challenge. Serologic tests performed early in infectious disease courses may have false-negative results, warranting convalescent testing when clinical suspicion is high.22 As such, an isolated negative serologic result might not have been followed by repeat testing had we not had strong suspicions. Ultimately, the positive PCR test result confirmed anaplasmosis, averting the need for convalescent serology.

The multitude of symptoms of these tick-borne diseases can make them diagnostic challenges in a clinical setting.8-12,20-22 Although anaplasmosis is rare, we considered the possibility of a tick-borne disease in our patient presenting with fever and meningoencephalitis. We needed to obtain diagnostic confirmation as quickly as possible to initiate treatment; however, understanding that there would be a substantial delay in diagnosis, we treated the patient empirically with doxycycline, which proved effective.14

Cases of tick-borne diseases such as Lyme disease, anaplasmosis, babesiosis, and Powassan virus infection are becoming increasingly more common in eastern Canada, including in eastern and now southwestern Ontario.3,5,16,18,20 At present, no vaccines exist for tick-borne diseases, with such vaccines still in concept and development.23

As one of the first reported cases of anaplasmosis in southwestern Ontario, this report highlights the importance of maintaining a high degree of suspicion and considering tick-borne infection in the differential diagnosis of patients presenting with unusual or severe manifestations, particularly when the history supports the possibility of tick exposure.

▸ Consider tick-borne illness even in patients presenting with nonspecific symptoms.

▸ Consider empirical treatment while awaiting confirmatory tests if there is a high degree of suspicion.

▸ Factor in real-world laboratory limitations when planning treatment for suspected tick-borne illness.

▸ Do not allow familiarity with common conditions to prevent consideration of a rare differential diagnosis.

▸ Consider that climate change is shifting vector-borne disease patterns geographically.

▸ Envisagez une maladie transmise par les tiques même chez des patients présentant des symptômes non spécifiques.

▸ Considérez un traitement empirique en attendant des tests de confirmation en présence d’un fort degré de suspicion.

▸ Prenez en compte les limites réelles des laboratoires dans la planification du traitement lorsqu’une maladie transmise par les tiques est soupçonnée.

▸ Ne laissez pas vos connaissances des problèmes courants vous empêcher d’envisager un diagnostic différentiel rare.

▸ Prenez en considération que le changement climatique influe sur les tendances des maladies à transmission vectorielle sur le plan géographique.