How many Lyme disease cases were reported in Ontario?

Ontario reported 2,369 confirmed and probable Lyme disease cases in 2024, according to the Public Health Agency of Canada’s Health Infobase annual tick-borne disease report. That is a 27% increase over the 1,859 cases reported in 2023, and about 41% of Canada’s national total of 5,809 cases that year — the largest count of any province. 2024 is the most recent year for which a final provincial figure has been published.

Is there an Ontario Lyme disease case count for 2025?

No. As of July 2026, neither Public Health Ontario nor the Public Health Agency of Canada had published a final 2025 Lyme disease case count for Ontario or for Canada. The latest published year is 2024. Public Health Ontario’s Vector-Borne Disease Tool publishes provisional year-to-date counts during the season, but those are revised as cases are investigated and classified and are not a substitute for a finalised annual figure. If you see a 2025 Ontario total quoted anywhere, check whether it traces back to one of those two agencies.

Which Ontario Public Health Units have the highest Lyme case counts?

We do not publish a public-health-unit ranking, and you should be sceptical of any that you find. PHAC’s national annual report gives provincial totals, not Ontario counts broken down by health unit. Public Health Ontario maps blacklegged tick risk areas through its Vector-Borne Disease Tool, and those risk areas are drawn as geographic areas rather than along health unit boundaries — a single health unit can contain both risk areas and non-risk areas. Check the current map for your own address rather than relying on a regional ranking.

Is the GTA inside the Lyme disease risk zone?

Blacklegged ticks are present in parts of southern Ontario including the Greater Toronto Area, and migratory birds deposit ticks well outside established populations every spring. Rather than relying on a blanket statement about a city or region, check Public Health Ontario’s Vector-Borne Disease Tool risk-area map for your own area, and do a tick check after any outdoor activity — including dog walks in city parks and ravines.

What can I do to reduce my household risk?

Three layers: (1) Yard — habitat modification (leaf-litter removal, short mowing, a gravel or wood-chip buffer between lawn and forest edge) plus a professional tick barrier treatment on the perimeter zones where ticks concentrate. Each application leaves up to 30 days of residual, so a season program is five treatments spread roughly monthly from May through September — enough to stay covered across peak nymph activity in May–July and through adult activity in the autumn, and to keep renewing the barrier as deer, mice and birds carry new ticks in from adjacent woodland. (2) Personal — DEET or icaridin on skin, permethrin on outdoor clothing, light-coloured clothing, and a daily tick check, since Lyme transmission generally requires 24 to 36 hours of attachment. (3) Medical — know the symptoms (an expanding rash, often but not always a bullseye, plus fever, fatigue and joint pain) and see a doctor promptly after a known bite. Early antibiotic treatment is highly effective.

Lyme Disease Cases Ontario: 2,369 in 2024

Q: Why are Lyme cases climbing in Ontario?

Two mechanisms are well documented in the peer-reviewed literature. First, temperature: blacklegged tick populations need enough accumulated warmth to complete their life cycle, and published models use cumulative annual degree-days above 0°C. Below roughly 2,800 degree-days above 0°C, Ixodes scapularis populations cannot establish or persist (Ghanbari et al., PLOS One 2025, citing Ogden et al. 2005). As accumulated degree-days rise, previously unsuitable areas become suitable. Second, dispersal: Ogden and colleagues estimated that migratory birds carry 50 to 175 million Ixodes scapularis ticks into Canada each spring (Applied and Environmental Microbiology, 2008). Improved recognition and diagnosis also contribute to the reported count, though the surveillance trend itself is sustained.

Quick Answer

Ontario reported 2,369 confirmed and probable Lyme disease cases in 2024 — up 27% over 2023, and about 41% of Canada’s national total. 2024 is the most recent year the Public Health Agency of Canada has published. There is no published 2025 Ontario figure.

Ontario: 1,478 cases (2022), 1,859 (2023), 2,369 (2024) — PHAC Health Infobase.
Canada: 4,785 cases (2023) and 5,809 (2024); national incidence rose from 11.9 to 14.1 per 100,000.
Ontario had the largest absolute count of any province in 2024, at roughly 41% of the national total.
No 2025 Ontario or national total has been published by Public Health Ontario or PHAC as of July 2026.
PHAC does not break Ontario down by public health unit in this report, so no PHU ranking appears here.
Lyme transmission generally requires 24–36 hours of tick attachment, so a daily tick check is the highest-leverage habit.

— BuzzSkito, GTA mosquito & tick control · 150+ five-star Google reviews. General information, not medical advice.

TL;DR: Ontario reported 2,369 confirmed and probable Lyme disease cases in 2024, up 27% on the year before and the highest count of any Canadian province. That is the newest published year — there is no 2025 number yet. The trend is real and sustained, and it is the reason yard-level tick control has become a mainstream request in the GTA.

The latest published number

2,369 confirmed and probable Lyme disease cases in Ontario in 2024. The source is the Public Health Agency of Canada’s Health Infobase annual report on Lyme disease and other tick-borne diseases surveillance in Canada, which compiles what the provinces and territories report to PHAC.

2022: 1,478 Ontario cases
2023: 1,859 Ontario cases — 39% of the national total
2024: 2,369 Ontario cases — 41% of the national total, up 27% year over year

Nationally, Canada went from 4,785 reported cases in 2023 to 5,809 in 2024, and national incidence rose from 11.9 to 14.1 per 100,000 people. PHAC does not publish a separate Ontario incidence rate in this report, so none is quoted here.

Two older Ontario figures, and why they sit apart

Public Health Ontario has published its own Ontario counts through a different surveillance product with a different reporting cut: 959 cases in 2017 (an incidence of 6.7 per 100,000, roughly three times the 2012–2016 average) and 612 cases in 2018. Those numbers are real, but they should not be plotted as one continuous line with the PHAC series above — the case definitions and reporting cutoffs differ, and joining them would overstate the slope.

What we do not know

Two things are worth stating plainly, because both get invented online:

There is no 2025 Ontario total. As of July 2026, neither Public Health Ontario nor PHAC has published a finalised 2025 case count for Ontario or for Canada. Public Health Ontario’s Vector-Borne Disease Tool shows provisional year-to-date counts during the season, but those are revised as cases are investigated and reclassified. If you see a specific 2025 Ontario figure quoted, trace it to one of those two agencies before you repeat it.
There is no public-health-unit ranking here. PHAC’s annual report reports by province, not by Ontario health unit. And Public Health Ontario maps tick risk as geographic risk areas, not along health unit boundaries — one health unit routinely contains both risk areas and non-risk areas. A ranked list of health units by case count would imply a precision the published data does not have.

For the current risk-area map covering your own address, go to Public Health Ontario’s Vector-Borne Disease Tool, which is redrawn annually.

Why the trend is climbing

Two mechanisms are well established in the peer-reviewed literature.

1. Accumulated warmth, not a single cold snap

Blacklegged tick populations need enough cumulative warmth to complete their two-year life cycle. Published models measure this as cumulative annual degree-days above 0°C rather than as a winter minimum temperature. Below roughly 2,800 degree-days above 0°C, Ixodes scapularis populations cannot establish or persist (Ghanbari et al., PLOS One 2025, citing Ogden et al. 2005). As accumulated degree-days rise, areas that could not previously support a self-sustaining tick population begin to.

2. Birds move ticks constantly

Migratory songbirds carry tick larvae and nymphs north every spring. Ogden and colleagues estimated that 50 to 175 million Ixodes scapularis ticks are dispersed into Canada annually this way (Applied and Environmental Microbiology, 2008). That means ticks are being seeded into new areas continuously, and a growing share of those areas can now hold them year-round.

Better clinical recognition and testing also lift the reported count. That is a real effect, but it does not account for the whole trend — the surveillance signal has been sustained across many years and multiple reporting systems.

What this means for your household

If you have a yard in southern Ontario that borders forest, ravine, conservation land, or any naturalized corridor, the practical question is not whether a tick will ever turn up. It is whether you have a routine that catches it. The single most useful fact: Lyme transmission from a blacklegged tick generally requires 24 to 36 hours of attachment, which is why a daily tick check during the May-to-July nymph window does more than almost anything else.

The household plan

Yard — habitat modification first (clear leaf litter from edges, mow short, put a gravel or wood-chip buffer between lawn and forest edge), then a professional barrier treatment on the perimeter zones where ticks actually sit. Each application holds up to 30 days of residual, so the season program is five treatments spread roughly monthly from May through September. A late-spring-and-late-summer pair would leave a multi-month hole straight through the May–July nymph peak — the worst stretch to be uncovered — and wildlife moving in off the ravine restocks the property all season regardless.
Personal protection — DEET or icaridin on skin, permethrin on outdoor clothing, light colours, and a full check within a couple of hours of coming inside.
Pets — veterinary tick preventatives (Bravecto, NexGard, Simparica) plus a physical check of ears, between toes, and the chest and belly.
Medical awareness — an expanding rash (often but not always a bullseye), fever, fatigue, and joint pain in the 3 to 30 days after a bite all warrant a prompt doctor visit. Early antibiotic treatment is highly effective.
Tick removal — fine-tipped tweezers, pull straight out without twisting, keep the tick, and watch the bite site.

The Ontario Lyme tracker

We maintain an Ontario Lyme disease tracker with the full published case series, the source for every figure, and tick-submission contacts for all 34 Ontario public health units. Every number on it is traceable to a citable primary source.

Lyme Disease Cases in Ontario: What the Latest Published Data Shows