Lyme disease spirochete, Borrelia burgdorferi, endemic in epicenter at Turkey Point, Ontario

Monitoring Risk: Tick and Borrelia burgdorferi Public Participatory Surveillance in the Canadian Maritimes, 2012-2020

Ticks are vectors of many diseases, including Lyme disease (Ld). Lyme disease is an emerging disease in Canada caused by infection with the Lyme borreliosis (Lb) members of the Borrelia genus of spirochaete bacteria, of which Borrelia burgdorferi is regionally the most prevalent. The primary tick vector in central and eastern Canada, Ixodes scapularis, is increasing in numbers and in the geographical extent of established populations. This study documents the distribution of ticks recovered by passive surveillance, and their B. burgdorferi infection prevalence, in three Canadian Maritime provinces from 2012-2020. These regions represent areas in which tick populations are widely established, establishing, and considered non-established. Using a community science approach by partnering with veterinarians and members of the public, we collected over 7000 ticks from the 3 provinces. The three species found most often on companion animals and humans were I. scapularis (76.9%), Ixodes cookei (10.4%) and Dermacentor variabilis (8.9%). The most common hosts were dogs (60.5%), cats (16.8%) and humans (17.6%). As is typical of passive surveillance tick collections, the majority of ticks recovered were adult females; for I. scapularis 90.2%, 5.3%, 3.9% and 0.6% of the total of 5630 ticks recovered for this species were adult females, adult males, nymphs and larvae, respectively. The majority of B. burgdorferi-infected ticks were I. scapularis, as expected. Borrelia infection prevalence in I scapularis was higher in Nova Scotia (20.9%), the province with the most endemic regions, than New Brunswick (14.1%) and Prince Edward Island (9.1%), provinces thought to have established and non-established tick populations, respectively. The province-wide Borrelia infection prevalence generally increased in these latter tow provinces over the course of the study. The host did not have a significant effect on B. burgdorferi infection prevalence; I. scapularis ticks from dogs, cats, humans was, 13.3% (n = 3622), 15.6% (n = 817), 17.9% (n = 730), respectively. No I. scapularis larvae were found infected (n = 33) but B. burgdorferi was detected in 14.8% of both adults (n = 5140) and nymphs (n = 215). The incidence of B. burgdorferi infection also did not differ by engorgement status 15.0% (n = 367), 15.1% (n = 3101) and 14.4% (n = 1958) of non-engorged, engorged and highly engorged ticks, respectively, were infected. In New Brunswick, at the advancing front of tick population establishment, the province-wide infection percentages generally increased over the nine-year study period and all health district regions showed increased tick recoveries and a trend of increased percentages of Borrelia-infected ticks over the course of the study. Within New Brunswick, tick recoveries but not Borrelia infection prevalence were significantly different from endemic and non-endemic regions, suggesting cryptic endemic regions existed prior to their designation as a risk area. Over the 9 years of the study, tick recoveries increased in New Brunswick, the primary study region, and I. scapularis recoveries spread northwards and along the coast, most but not all new sites of recoveries were predicted by climate-based models, indicating that ongoing tick surveillance is necessary to accurately detect all areas of risk. Comparison of tick recoveries and public health risk areas indicates a lag in identification of risk areas. Accurate and timely information on tick distribution and the incidence of Borrelia and other infections are essential for keeping the public informed of risk and to support disease prevention behaviors.

Monitoring of Nesting Songbirds Detects Established Population of Blacklegged Ticks and Associated Lyme Disease Endemic Area in Canada

This study provides a novel method of documenting established populations of bird-feeding ticks. Single populations of the blacklegged tick, Ixodes scapularis, and the rabbit tick, Haemaphysalis leporispalustris, were revealed in southwestern Québec, Canada. Blacklegged tick nymphs and, similarly, larval and nymphal rabbit ticks were tested for the Lyme disease bacterium, Borrelia burgdorferi sensu lato (Bbsl), using PCR and the flagellin (flaB) gene, and 14 (42%) of 33 of blacklegged tick nymphs tested were positive. In contrast, larval and nymphal H. leporsipalustris ticks were negative for Bbsl. The occurrence of Bbsl in I. scapularis nymphs brings to light the presence of a Lyme disease endemic area at this songbird nesting locality. Because our findings denote that this area is a Lyme disease endemic area, and I. scapularis is a human-biting tick, local residents and outdoor workers must take preventive measures to avoid tick bites. Furthermore, local healthcare practitioners must include Lyme disease in their differential diagnosis.

Detection and Transstadial Passage of Babesia Species and Borrelia burgdorferi Sensu Lato in Ticks Collected from Avian and Mammalian Hosts in Canada

Lyme disease and human babesiosis are the most common tick-borne zoonoses in the Temperate Zone of North America. The number of infected patients has continued to rise globally, and these zoonoses pose a major healthcare threat. This tick-host-pathogen study was conducted to test for infectious microbes associated with Lyme disease and human babesiosis in Canada. Using the flagellin (flaB) gene, three members of the Borrelia burgdorferi sensu lato (Bbsl) complex were detected, namely a Borrelia lanei-like spirochete, Borrelia burgdorferi sensu stricto (Bbss), and a distinct strain that may represent a separate Bbsl genospecies. This novel Bbsl strain was detected in a mouse tick, Ixodes muris, collected from a House Wren, Troglodytes aedon, in Quebec during the southward fall migration. The presence of Bbsl in bird-feeding larvae of I. muris suggests reservoir competency in three passerines (i.e., Common Yellowthroat, House Wren, Magnolia Warbler). Based on the 18S ribosomal RNA (rRNA) gene, three Babesia species (i.e., Babesia divergens-like, Babesia microti, Babesia odocoilei) were detected in field-collected ticks. Not only was B. odocoilei found in songbird-derived ticks, this piroplasm was apparent in adult questing blacklegged ticks, Ixodes scapularis, in southern Canada. By allowing live, engorged ticks to molt, we confirm the transstadial passage of Bbsl in I. muris and B. odocoilei in I. scapularis. Bbss and Babesia microti were detected concurrently in a groundhog tick, Ixodes cookei, in Western Ontario. In Alberta, a winter tick, Dermacentor albipictus, which was collected from a moose, Alces alces, tested positive for Bbss. Notably, a B. divergens-like piroplasm was detected in a rabbit tick, Haemaphysalis leporispalustris, collected from an eastern cottontail in southern Manitoba; this Babesia species is a first-time discovery in Canada. This rabbit tick was also co-infected with Borrelia lanei-like spirochetes, which constitutes a first in Canada. Overall, five ticks were concurrently infected with Babesia and Bbsl pathogens and, after the molt, could potentially co-infect humans. Notably, we provide the first authentic report of I. scapularis ticks co-infected with Bbsl and B. odocoilei in Canada. The full extent of infectious microorganisms transmitted to humans by ticks is not fully elucidated, and clinicians need to be aware of the complexity of these tick-transmitted enzootic agents on human health. Diagnosis and treatment must be administered by those with accredited medical training in tick-borne zoonosis.

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

We identified ticks submitted by the public from 2008 through 2012 in Ontario, Canada, and tested blacklegged ticks Ixodes scapularis for Borrelia burgdorferi and Anaplasma phagocytophilum. Among the 18 species of ticks identified, I. scapularis, Dermacentor variabilis, Ixodes cookei and Amblyomma americanum represented 98.1% of the 14,369 ticks submitted. Rates of blacklegged tick submission per 100,000 population were highest in Ontario's Eastern region; D. variabilis in Central West and Eastern regions; I. cookei in Eastern and South West regions; and A. americanum had a scattered distribution. Rates of blacklegged tick submission per 100,000 population were highest from children (0-9 years old) and older adults (55-74 years old). In two health units in the Eastern region (i.e., Leeds, Grenville & Lanark District and Kingston-Frontenac and Lennox & Addington), the rate of submission for engorged and B. burgdorferi-positive blacklegged ticks was 47× higher than the rest of Ontario. Rate of spread for blacklegged ticks was relatively faster and across a larger geographic area along the northern shore of Lake Ontario/St. Lawrence River, compared with slower spread from isolated populations along the northern shore of Lake Erie. The infection prevalence of B. burgdorferi in blacklegged ticks increased in Ontario over the study period from 8.4% in 2008 to 19.1% in 2012. The prevalence of B. burgdorferi-positive blacklegged ticks increased yearly during the surveillance period and, while increases were not uniform across all regions, increases were greatest in the Central West region, followed by Eastern and South West regions. The overall infection prevalence of A. phagocytophilum in blacklegged ticks was 0.3%. This study provides essential information on ticks of medical importance in Ontario, and identifies demographic and geographic areas for focused public education on the prevention of tick bites and tick-borne diseases.

Estimated effects of projected climate change on the basic reproductive number of the Lyme disease vector Ixodes scapularis

BACKGROUND

The extent to which climate change may affect human health by increasing risk from vector-borne diseases has been under considerable debate.

OBJECTIVES

We quantified potential effects of future climate change on the basic reproduction number (R0) of the tick vector of Lyme disease, Ixodes scapularis, and explored their importance for Lyme disease risk, and for vector-borne diseases in general.

METHODS

We applied observed temperature data for North America and projected temperatures using regional climate models to drive an I. scapularis population model to hindcast recent, and project future, effects of climate warming on R0. Modeled R0 increases were compared with R0 ranges for pathogens and parasites associated with variations in key ecological and epidemiological factors (obtained by literature review) to assess their epidemiological importance.

RESULTS

R0 for I. scapularis in North America increased during the years 1971-2010 in spatio-temporal patterns consistent with observations. Increased temperatures due to projected climate change increased R0 by factors (2-5 times in Canada and 1.5-2 times in the United States), comparable to observed ranges of R0 for pathogens and parasites due to variations in strains, geographic locations, epidemics, host and vector densities, and control efforts.

CONCLUSIONS

Climate warming may have co-driven the emergence of Lyme disease in northeastern North America, and in the future may drive substantial disease spread into new geographic regions and increase tick-borne disease risk where climate is currently suitable. Our findings highlight the potential for climate change to have profound effects on vectors and vector-borne diseases, and the need to refocus efforts to understand these effects.

Borrelia bissettii isolates induce pathology in a murine model of disease

The spirochete Borrelia burgdorferi is a tick-borne pathogen that causes Lyme disease. Although B. burgdorferi sensu lato is a diverse group of bacteria, only three genospecies, B. burgdorferi sensu stricto, Borrelia afzelii, and Borrelia garinii, are known to be pathogenic and commonly recognized to cause human disease. To assess the potential of another common genospecies, Borrelia bissettii, to induce disease, a mouse model was employed. Two Colorado isolates of B. bissettii (CO-Bb) induced lesions of the bladder, heart, and femorotibial joint 8 weeks after inoculation into mice. In contrast, two British Columbia (BC-Bb) isolates, could not be cultured or amplified by PCR from target organs, and did not induce lesions. Consistent with pathology and culture results, the antibody response in mice to BC-Bb was minimal compared to CO-Bb, indicating either transient localized infection or rapid immune clearance of BC-Bb. Although sequence analysis of the rrf (5S)-rrl (23S) intergenic spacer region indicated 99% homology between CO-Bb and BC-Bb, polyacrylamide gel electrophoresis (PAGE) analysis indicated five distinct protein differences between these low-passage isolates. These studies support the prospect that B. bissettii may indeed be the causative agent of Lyme borreliosis cases in Eastern Europe, associated with the atypical Borrelia strain 25015, and in other regions. To our knowledge, this is the first evidence that B. bissettii can induce pathology in a vertebrate host.

Distribution and characterization of Borrelia burgdorferi isolates from Ixodes scapularis and presence in mammalian hosts in Ontario, Canada

The blacklegged tick, Ixodes scapularis Say (Acari: Ixodidae), has a wide geographical distribution in Ontario, Canada, with a detected range extending at least as far north as the 50th parallel. Our data of 591 adult I. scapularis submissions collected from domestic animals (canines, felines, and equines) and humans during a 10-yr period (1993-2002) discloses a monthly questing activity in Ontario that peaks in May and October. The Lyme disease spirochete Borrelia burgdorferi Johnson, Schmidt, Hyde, Steigerwalt & Brenner was detected in 12.9% of I. scapularis adults collected from domestic hosts with no history of out-of-province travel or exposure at a Lyme disease endemic area. Fifty-three isolates of B. burgdorferi were confirmed positive with polymerase chain reaction by targeting the rrf (5S)-rrl (23S) gene. Using DNA sequencing of the ribosomal species-specific rrf (5S) -rrl (23S) intergenic spacer region, all isolates belong to the pathogenic genospecies B. burgdorferi sensu stricto (s.s.). Nucleotide sequence analysis of a 218- to 220-bp amplicon fragment exhibits six cluster patterns and, collectively, these isolates branch into four phylogenetic cluster groups for both untraveled, mammalian hosts and those with travel to the northeastern United States (New Jersey and New York). Four of five geographic regions in Ontario had strain variants consisting of three different genomic cluster groups. Overall, our molecular characterization of B. burgdorferi s.s. shows genetic heterogeneity within Ontario and displays a connecting link to common strains from Lyme disease endemic areas in the northeastern United States. Moreover, our findings of B. burgdorferi in I. scapularis reveal that people and domestic animals may be exposed to Lyme disease vector ticks, which have wide-ranging distribution in eastern and central Canada.

Investigation of ground level and remote-sensed data for habitat classification and prediction of survival of Ixodes scapularis in habitats of southeastern Canada

In southeastern Canada, most populations of Ixodes scapularis Say, the Lyme disease vector, occur in Carolinian forests. Climate change projections suggest a northward range expansion of I. scapularis this century, but it is unclear whether more northerly habitats are suitable for I. scapularis survival. In this study, we assessed the suitability of woodlands of the Lower Great Lakes/St. Lawrence Plain region for I. scapularis by comparing tick egg survival in four different woodlands. Woodlands where I. scapularis are established, and sand dune where I. scapularis do not survive, served as positive and negative control sites, respectively. At two woodland sites, egg survival was the same as at the positive control site, but at two of the sites survival was significantly less than either the positive control site, or one of the other test sites. Egg survival in all woodland sites was significantly higher than in the sand dune site. Ground level habitat classification discriminated among woodlands in which tick survival differed. The likelihood that I. scapularis populations could persist in the different habitats, as deduced using a population model of I. scapularis, was significantly associated with variations in Landsat 7 ETM+ data (normalized difference vegetation index [NDVI] and Tasselled Cap indices). The NDVI index predicted habitat suitability at Long Point, Ontario, with high sensitivity but moderate specificity. Our study suggests that I. scapularis populations could establish in more northerly woodland types than those in which they currently exist. Suitable habitats may be detected by ground-level habitat classification, and remote-sensed data may assist this process.

Investigation of ground level and remote-sensed data for habitat classification and prediction of survival of Ixodes scapularis in habitats of southeastern Canada

In southeastern Canada, most populations of Ixodes scapularis Say, the Lyme disease vector, occur in Carolinian forests. Climate change projections suggest a northward range expansion of I. scapularis this century, but it is unclear whether more northerly habitats are suitable for I. scapularis survival. In this study, we assessed the suitability of woodlands of the Lower Great Lakes/St. Lawrence Plain region for I. scapularis by comparing tick egg survival in four different woodlands. Woodlands where I. scapularis are established, and sand dune where I. scapularis do not survive, served as positive and negative control sites, respectively. At two woodland sites, egg survival was the same as at the positive control site, but at two of the sites survival was significantly less than either the positive control site, or one of the other test sites. Egg survival in all woodland sites was significantly higher than in the sand dune site. Ground level habitat classification discriminated among woodlands in which tick survival differed. The likelihood that I. scapularis populations could persist in the different habitats, as deduced using a population model of I. scapularis, was significantly associated with variations in Landsat 7 ETM+ data (normalized difference vegetation index [NDVI] and Tasselled Cap indices). The NDVI index predicted habitat suitability at Long Point, Ontario, with high sensitivity but moderate specificity. Our study suggests that I. scapularis populations could establish in more northerly woodland types than those in which they currently exist. Suitable habitats may be detected by ground-level habitat classification, and remote-sensed data may assist this process.

MIGRATORY SONGBIRDS DISPERSE TICKS ACROSS CANADA, AND FIRST ISOLATION OF THE LYME DISEASE SPIROCHETE, BORRELIA BURGDORFERI, FROM THE AVIAN TICK, IXODES AURITULUS

During a 3-yr comprehensive study, 196 ixodid ticks (9 species) were collected from 89 passerine birds (32 species) from 25 localities across Canada to determine the distribution of avian-associated tick species and endogenous Lyme disease spirochetes, Borrelia burgdorferi Johnson, Schmid, Hyde, Steigerwalt, and Brenner. We report the following first records of tick parasitism on avian hosts: the rabbit-associated tick, Ixodes dentatus Marx, from Manitoba and Ontario; the mouse tick, Ixodes muris Bishopp and Smith, from British Columbia; and the blacklegged tick, Ixodes scapularis Say, from New Brunswick. Moreover, we provide the first record of the Neotropical tick, Amblyomma humerale Koch (1 nymph), in Canada and its parasitism of any bird. This tick was compared morphologically with nymphs of other Neotropical Amblyomma spp., and genetically, using a 344-bp fragment of the 12S rDNA sequence of 41 New World Amblyomma species. The first collections of the western blacklegged tick, Ixodes pacificus Cooley and Kohls, from passerine species in Alberta and British Columbia, are also reported. Notably, we further report the first isolation of B. burgdorferi from the bird tick, Ixodes auritulus Neumann, collected from an American robin, Turdus migratorius L., on Vancouver Island. Furthermore, B. burgdorferi-positive I. auritulus larvae were collected from a reservoir-competent fox sparrow, Passerella iliaca (Merrem). Our findings indicate that ground-dwelling passerines, in particular, are parasitized by certain ixodid ticks and play an important role across Canada in the wide dispersal of B. burgdorferi-infected ticks and increased risk of Lyme disease exposure.