One Risk Area to a Province: The Twelve Years That Made Manitoba the Western Frontier of Lyme Disease

1. Introduction: a frontier that moved

Most of the range shifts discussed in this journal are inferred from mechanism. This one was measured, by a provincial programme, over twelve years, and the before and after are unusually clear.

1.1 Why it belongs in a pest management journal

Ticks are a public health matter rather than a structural pest problem, and we treat them as such here. But the professional question this raises is general: a species established itself across most of a province's populated area within the span of a single career, and the surveillance that documented it is the kind of thing this journal has repeatedly argued is missing for other species.

2. The Manitoba record

The provincial account is compact and worth setting out in full.

Passive, or citizen supported, tick surveillance has been ongoing in Manitoba since 1995. Active surveillance of blacklegged ticks to identify risk areas was carried out in Manitoba between 2006 and 2018. In 2006, only one risk area was identified, in the extreme southeast corner of the province. By 2018, the rapid range expansion of blacklegged ticks was demonstrated throughout much of southern Manitoba, south of the 53rd parallel, wherever suitable habitat is present.¹

2.1 What the 2006 finding represents

A single risk area in the extreme southeast is what a range edge looks like. Southeastern Manitoba adjoins northwestern Ontario and Minnesota, both of which had established populations, so the first Manitoba establishment occurring at the point of nearest contact is exactly the pattern a range-expansion model would predict.

2.2 What changed in twelve years

The province describes the change as rapid range expansion demonstrated throughout much of southern Manitoba.¹ That covers the great majority of the province's population and essentially all of its agricultural and cottage country.

A resident who formed their understanding of tick risk before 2006 formed it in a province with one known risk area. That understanding is now wrong for most of where they live.

3. The 53rd parallel

The boundary given is specific enough to be useful, which is rare in range descriptions.

Expansion is described as occurring south of the 53rd parallel wherever suitable habitat is present.¹

3.1 Reading the qualifier

The phrase wherever suitable habitat is present does substantial work. The parallel is not a wall and the distribution below it is not continuous. Blacklegged ticks require particular conditions, principally deciduous or mixed woodland with leaf litter providing the humidity they need to avoid desiccation.

Open prairie, cultivated field and mown grass do not supply that. The practical boundary is therefore habitat within a latitude rather than the latitude itself, and the relevant risk map is one of woodland edge.

3.2 The risk gradient

The province notes that disease risk is relatively low outside southern Manitoba because the chance of encountering infected blacklegged ticks is less likely there.¹

That is a carefully phrased statement. It concerns probability of encounter rather than absolute absence, which is the correct framing for a species whose range edge is moving.

4. Where Manitoba sits nationally

The national picture establishes why this province is the interesting case.

Lyme disease is the most commonly reported vector-borne disease in Canada, caused by Borrelia burgdorferi and transmitted through the bite of an infectious tick: the blacklegged tick, Ixodes scapularis, in Manitoba, central and eastern Canada, and the western blacklegged tick, Ixodes pacificus, in British Columbia.²

In Alberta and Saskatchewan, no known endemic areas of blacklegged tick populations have been detected.²

4.1 The frontier position

Manitoba is therefore the westernmost province with established populations, which makes it the current western edge of Lyme disease risk in Canada.

In 2019 the majority of locally reported cases were concentrated in southern Manitoba, southern and southeastern Ontario, southern Quebec and Nova Scotia.² Manitoba appears first in that list and is the only prairie province in it.

4.2 The national trend

Over the past decade, the northward geographic range expansion of blacklegged tick populations in southeastern and south-central Canada, in part due to climate warming, has resulted in an increase in the number of locally acquired Lyme disease cases.⁶

Manitoba's twelve-year record is a provincial instance of a continental pattern.

5. Passive surveillance

The two surveillance modes answer different questions and the distinction matters.

Manitoba's passive programme has run since 1995 and depends on members of the public submitting ticks they encounter.¹

5.1 What it is good at

Passive surveillance achieves geographic coverage no active programme could afford, and it has demonstrable value in detection. Work in Ontario found passive surveillance identifying an area where tick populations were developing over a broad geographic area rather than in the focal manner seen with historical populations, and concluded that as climate change increases habitat suitability, passive surveillance will play a key role in detecting populations that pose a threat to public health.⁵

5.2 Its structural bias

A submitted tick records where a person was, not where ticks are. Submissions concentrate where people walk, where they notice attached ticks, and where they know a submission programme exists.

This is the same bias this journal identified in complaint-driven rodent surveillance, and it has the same consequence: the data are informative about presence and close to useless for absence.

6. Active surveillance

Active surveillance replaces public submission with deliberate sampling, usually by drag sampling, in which cloth is drawn over vegetation and questing ticks attach to it.

Manitoba conducted active surveillance specifically to identify risk areas between 2006 and 2018.¹

6.1 Why it is the one that establishes establishment

A tick submitted by a member of the public may have been carried in on a migrating bird or a dog returning from elsewhere. Finding ticks repeatedly, across life stages, at a defined site, over successive seasons, is what distinguishes a reproducing population from an arriving individual.

That distinction is the difference between a species being present and a place being a risk area.

6.2 Site selection

Active programmes cannot sample everywhere, so selection matters. The approach used in Saskatchewan prioritises locations with the highest likelihood of supporting an established tick population, drawing on computer models, information from the passive surveillance programme, any known human or animal cases of Lyme disease, and information from nearby jurisdictions.⁴

Note that passive surveillance feeds active site selection. The two are complementary in the same way bioassay and molecular screening are complementary in the resistance article published elsewhere in this journal.

7. Establishing establishment

The methodological question of how you decide a population is established has a published answer, demonstrated in an Ottawa study.

Researchers evaluated the degree of I. scapularis population establishment and Borrelia burgdorferi occurrence using active surveillance at 28 sites from 2017 to 2019. They used a field indicator tool developed by Clow and colleagues to determine the risk of establishment for each tick cohort at each site using the results of drag sampling.³

7.1 The cohort design

Each site was assigned an ecological classification describing the pattern of tick colonisation over two successive cohorts, where cohort one comprised ticks collected in autumn 2017 and spring 2018, and cohort two was collected in autumn 2018 and spring 2019.³

Pairing an autumn collection with the following spring reflects the tick's life cycle rather than the calendar year, which is what makes successive cohorts comparable.

7.2 The classification outcome

Sites were classified into categories including high-stable and emerging, describing not merely whether ticks were present but what trajectory the population was on.³

A classification that distinguishes an established population from one arriving is more useful than a presence map, because it indicates where risk is already realised and where it is developing.

8. Infection is not uniform across sites

The Ottawa study produced a finding that matters for how risk should be communicated.

B. burgdorferi infected ticks were found at all high-stable sites, and at one emerging site. The authors concluded that high-stable sites pose a risk.³

8.1 Why the sequence makes sense

The pathogen requires a maintained transmission cycle between ticks and reservoir hosts. A newly arrived tick population has not necessarily had time to establish that cycle, so infection generally follows establishment rather than accompanying it.

The emerging site with infected ticks indicates the lag can be short or absent, which argues against treating newly colonised areas as safe.

9. The temperature argument

The mechanism behind the expansion is the best supported element of this literature, and it connects directly to the thermal arguments made elsewhere in this journal.

The evidence clearly demonstrates that temperature is a key driver, or co-driver, of Lyme disease risk emergence through its impact on vector tick distributions and abundance, and subsequently on B. burgdorferi transmission cycle occurrence.⁷

9.1 The explicit statement of a cold limit

Empirical data support the notion that climate limits the distribution of blacklegged ticks in Canada, and the reality that some regions of the country are too cold to support tick populations.⁷

This is an unusually direct statement of a thermal boundary, and it is the same structure as the urban ecology argument published in this journal: a species whose northern limit is set by cold, in a region where cold is changing.

9.2 The spatial evidence

Early field studies on range expansion in Quebec determined that tick populations established in the warmest portions of the province first, and additional field surveillance in eastern Canada supported the importance of temperature in determining the spatial pattern of establishment at a multiprovince geographic scale.⁷

Establishment following the temperature gradient rather than simply the distance gradient is the observation that distinguishes a climate-driven expansion from ordinary dispersal.

9.3 The Manitoba implication

If the limit is thermal and the boundary is moving, then the 53rd parallel description is a snapshot rather than a fixed line, and the province's own framing of relatively lower risk outside southern Manitoba¹ is a statement about the present distribution.

This also explains Saskatchewan's position. It is not that ticks cannot reach Saskatchewan; it is that conditions there have not yet supported establishment.

10. What Saskatchewan is doing

The neighbouring programme is instructive because it is watching for a transition Manitoba has already made.

In order to maximise the probability of finding any risk areas, meaning sites with established blacklegged tick populations, the Saskatchewan active surveillance programme prioritises locations with the highest likelihood of supporting an established population. If such populations were found, these would be the first Lyme disease risk areas known in Saskatchewan.⁴

10.1 The value of watching a boundary

Saskatchewan is running the surveillance that Manitoba ran between 2006 and 2018,¹ in a jurisdiction currently on the far side of the boundary.

If the thermal argument of §9 holds, the useful question is not whether Saskatchewan will find established populations but when, and the programme is designed to detect that transition rather than to confirm an absence.

11. The eTick transition

Manitoba changed how it collects passive surveillance data, and the change is worth noting.

Starting in April 2021, Manitoba Health, Seniors and Long-Term Care adopted the eTick image-based identification platform developed by researchers at Bishop's University and funded by the Public Health Agency of Canada.¹

11.1 What image-based identification changes

Physical submission requires the person to retain the specimen, package it and post it, with identification occurring days or weeks later. A photograph submitted at the time of removal returns identification far sooner, which matters because Lyme prophylaxis decisions are time-sensitive.

It also lowers the participation barrier, which should improve the geographic coverage that is passive surveillance's main strength.

11.2 The trade-off

A photograph cannot be tested for B. burgdorferi. Image-based platforms improve identification speed and reach while reducing the pathogen-testing yield that physical submission provides, unless specimens continue to be collected in parallel.

We raise that as a structural observation rather than a criticism, since we have not established how Manitoba handles specimen retention under the new platform.

12. What this means in Manitoba

The risk map changed within living memory. One risk area in 2006, much of southern Manitoba by 2018.¹ Anyone relying on older understanding is relying on a different province.

Habitat matters more than latitude. The expansion is described as occurring wherever suitable habitat is present,¹ which means woodland edge and leaf litter rather than open ground.

Established areas should be assumed to carry infected ticks. All high-stable sites in the Ottawa study had infected ticks.³

Submit what you find. The passive programme has run since 1995¹ and the image platform has made it straightforward.¹ Individual submissions are how boundary movement gets detected.

This is not a treatment problem. Nothing in this paper supports acaricide application as a general response, and the interventions with evidence behind them are personal protection, prompt removal, and habitat management at the woodland edge.

13. Limitations and open questions

Active surveillance appears to have ended in 2018. The provincial account gives 2006 to 2018 as the active period.¹ We do not know whether it continued in another form, and if it did not, the province's establishment map is now several years old at a time when the boundary is moving.

We have not consulted the annual reports. The provincial page refers to annual reports containing surveillance data and maps.¹ We have worked from the summary and a reader wanting the underlying data should go to those.

The establishment methodology is from Ottawa. The field indicator tool and cohort classification come from an Ontario study.³ Manitoba's classification criteria may differ.

National figures are from 2018 and 2019 editions. The provincial establishment status and case distribution are as reported then.²⁶ Saskatchewan's status in particular is the kind of thing that could change.

Our §11.2 point is inference. We have not established Manitoba's specimen retention practice under the image platform.

This is outside our practice. We are a structural pest control company. Tick surveillance and Lyme risk are public health matters and this is a review of published surveillance rather than professional guidance.

14. Conclusion

In 2006 Manitoba had one known blacklegged tick risk area, in the extreme southeast corner. By 2018 provincial surveillance had demonstrated rapid range expansion throughout much of southern Manitoba, south of the 53rd parallel, wherever suitable habitat is present.¹ Alberta and Saskatchewan have no known endemic populations,² which makes this province the western frontier of Lyme disease establishment in Canada.

The mechanism is reasonably well established. Temperature is a key driver of risk emergence through its effect on tick distribution and abundance, climate limits blacklegged tick distribution in Canada, some regions remain too cold to support populations, and establishment in Quebec occurred in the warmest portions of the province first.⁷

What we find most notable is the pace. This was not a slow drift. A province went from one identified risk area to province-wide southern establishment in twelve years, and the surveillance that documented it was running the whole time. Where other chapters of this journal have complained that nobody measured something, here somebody did, and the measurement is the reason anyone can state the change with confidence.

That is the argument for surveillance in a single case. Manitoba can describe what happened to its tick population between 2006 and 2018 because it was watching. It cannot say anything equivalent about its bed bug, rodent or stored product resistance status, for exactly the opposite reason.

References

1. Surveillance, Tick-Borne Diseases. Province of Manitoba, Health. Source for passive citizen supported tick surveillance ongoing since 1995, active surveillance of blacklegged ticks to identify risk areas carried out between 2006 and 2018, the identification of a single risk area in 2006 in the extreme southeast corner, the demonstration by 2018 of rapid range expansion throughout much of southern Manitoba south of the 53rd parallel wherever suitable habitat is present, the statement that disease risk is relatively low outside southern Manitoba because encountering infected blacklegged ticks is less likely, and the April 2021 adoption of the eTick image-based identification platform developed at Bishop's University and funded by the Public Health Agency of Canada. https://www.gov.mb.ca/health/publichealth/cdc/tickborne/surveillance.html
2. Lyme disease surveillance in Canada: Annual edition 2019. Public Health Agency of Canada. Source for Lyme disease as the most commonly reported vector-borne disease in Canada, transmission of Borrelia burgdorferi by Ixodes scapularis in Manitoba, central and eastern Canada and by Ixodes pacificus in British Columbia, the absence of known endemic areas of blacklegged tick populations in Alberta and Saskatchewan, and the concentration of locally reported cases in southern Manitoba, southern and southeastern Ontario, southern Quebec and Nova Scotia. https://www.canada.ca/en/public-health/services/publications/diseases-conditions/lyme-disease-surveillance-report-2019.html
3. Burrows, H., Talbot, B., McKay, R., Slatculescu, A., Logan, J., Thickstun, C., Lindsay, L.R., Dibernardo, A., Koffi, J.K., Ogden, N.H. & Kulkarni, M.A. (2021). A multi-year assessment of blacklegged tick (Ixodes scapularis) population establishment and Lyme disease risk areas in Ottawa, Canada, 2017–2019. PLOS ONE. doi:10.1371/journal.pone.0246484. Source for active surveillance at 28 sites, the field indicator tool developed by Clow and colleagues, the two-cohort design pairing autumn and following spring collections, the ecological classification of colonisation pattern, and the finding of B. burgdorferi infected ticks at all high-stable sites and at one emerging site. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7861446/
4. Tick Surveillance Report 2024 Summary. Government of Saskatchewan. Source for the prioritisation of active surveillance locations with the highest likelihood of supporting an established tick population, the use of computer models, passive surveillance information, known human or animal Lyme disease cases and information from nearby jurisdictions in selecting priority locations, and the statement that any populations found would be the first Lyme disease risk areas known in Saskatchewan. https://publications.saskatchewan.ca/api/v1/products/129557/formats/156219/download
5. Population-Based Passive Tick Surveillance and Detection of Expanding Foci of Blacklegged Ticks Ixodes scapularis and the Lyme Disease Agent Borrelia burgdorferi in Ontario, Canada. PLOS ONE. Source for the detection of tick populations developing over a broad geographic area rather than focally, and for the conclusion that passive tick surveillance will play a key role in detecting populations posing a public health threat as climate change increases habitat suitability. https://journals.plos.org/plosone/article?id=10.1371%2Fjournal.pone.0105358
6. Lyme disease surveillance in Canada: Annual edition 2018. Public Health Agency of Canada. Source for the statement that northward geographic range expansion of blacklegged tick populations in southeastern and south-central Canada over the past decade, in part due to climate warming, has resulted in an increase in locally acquired Lyme disease cases, and for the availability of acquisition location data for 69 per cent of locally acquired cases. https://www.canada.ca/en/public-health/services/publications/diseases-conditions/surveillance-lyme-disease-annual-edition-2018.html
7. Reply to Comment on Distribution of Ixodes scapularis in Northwestern Ontario. Source for the statement that temperature is a key driver or co-driver of Lyme disease risk emergence through its impact on vector tick distributions and abundance and subsequently on B. burgdorferi transmission cycle occurrence, that empirical data support climate limiting blacklegged tick distribution in Canada with some regions too cold to support populations, and that early Quebec field studies found populations establishing in the warmest portions of the province first with multiprovince surveillance supporting the importance of temperature in the spatial pattern of establishment. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6603982/