Abstract
Background and Methods:
This Lyme borreliosis (LB) and Borrelia burgdorferi sensu lato (Bbsl)-infected Ixodes ticks surveillance review—from the WHO regions of the Americas, Eastern Mediterranean, Europe, South-East Asia, and Western Pacific—is informed by LB cases or incidence, Bbsl antibody seroprevalence, and Ixodes (I.) tick surveillance results from publications (2005–2022) and recent government websites.
Results:
LB cases, by the WHO region—country, were documented in the following: the Americas—Brazil and México; Europe—Russian Federation and Türkiye; South-East Asia—India; and Western Pacific—Japan, Mongolia, and South Korea. Mean incidence, cases/100,000 population per year (country, period), was as follows: Europe, 4.8 (Russian Federation, 2009–2021); Western Pacific, 0.01 (Japan, 2005–2021) and 0.03 (South Korea, 2012–2021). Two-tier testing Bbsl antibody seroprevalence estimate ranges were as follows: the Americas, 1.0–6.2% (Brazil), 4.6% (Colombia), and 23.1% (México); Europe, 0–15.8% (Türkiye); South-East Asia, 0.4–3.0% (India); and Western Pacific, 0–14.0% (Mongolia). Ixodes tick surveillance was presented by species (nymph, adult, or not reported, NR, life stage and [Bbsl-infected proportion]): the Americas—México, I. scapularis (NR [34.2%]); Eastern Mediterranean—Iran, I. ricinus (adult [0.9% Borrelia]); Europe—Russian Federation, I. ricinus (nymph [27.3%], nymph/adult [33.4%], adult/NR [9.8–80.4%]) and I. persulcatus (adult/NR [12.0–75.3%]) and Türkiye, I. ricinus (adult/NR [19.9%]); and Western Pacific—Japan, I. persulcatus (nymph [0–10.0%], nymph/adult [1.8–23.6%], adult/NR [detected–up to 25.5%]) and Mongolia, I. persulcatus (nymph [detected], nymph/adult [49.4%], adult [7.0–49.7%]).
Conclusions:
LB burden might be underrecognized in certain countries of the Americas, Eastern Mediterranean, and South-East Asia, whereas LB cases or incidence, Bbsl antibody seroprevalence, and Bbsl-infected tick presence is established in certain countries of WHO Europe (Russian Federation and Türkiye) and Western Pacific (Japan, Korea, and Mongolia), and LB could be present in neighboring countries within these WHO regions (PROSPERO: CRD42021236906).
Introduction
Lyme borreliosis (LB) is caused by a Borrelia burgdorferi sensu lato (Bbsl) complex genospecies that can infect humans through Ixodes tick bites (Estrada-Pena et al., 2018; Margos et al., 2019; Radolf et al., 2021; Rauter and Hartung, 2005; Richter and Matuschka, 2006; Stanek and Strle, 2018; Stanek et al., 2012; Strnad et al., 2017; Woitzik and Linder, 2021; Wolcott et al., 2021). The Bbsl complex presently comprises at least 23 genospecies, although most human disease is caused by five genospecies (Borrelia [B.] burgdorferi sensu stricto [Bbss], B. afzelii, B. garinii [including closely related B. bavariensis], and B. spielmanii), with human disease, detected in specimens either from single cases or in a few patients, also caused by B. bissettiae, B. kurtenbachii, B. lusitaniae, B. mayonii, or B. valaisiana (Eisen, 2020; Radolf et al., 2021; Woitzik and Linder, 2021; Wolcott et al., 2021). Local Bbsl genospecies distribution determines the serology testing targets; consequently, the Bbss strain, B31, is used in the United States of America (USA), while LB in Europe is caused by 5–7 genospecies. Ixodes (I.) tick species infected with and capable of transmitting Bbsl genospecies causing LB are found in North America (Canada, USA) (I. scapularis and I. pacificus), the European Union (I. ricinus) (Marques et al., 2021), and Japan (I. persulcatus) (Lee et al., 2019; NIID: National Institute of Infectious Disease, 2023). There also has been recent evidence of Bbsl-infected ticks in China (Che et al., 2022; Guan et al., 2025). Adult ticks tend to be Bbsl-infected more often than nymphs, yet nymphs are more likely to infect humans (Estrada-Pena et al., 2018; Lernout et al., 2019).
The name LB is used in Eurasia, and Lyme disease (LD) is used primarily in North America (Canada, USA). Untreated LB might progress by clinical stages as follows: Stage 1 (early localized infection within days to weeks); Stage 2 (disseminated LB after weeks or months) from early as borrelial lymphocytoma to late including systemic Lyme neuroborreliosis (LNB) or Lyme carditis (Trevisan et al., 2020); and Stage 3 (late localized infections) such as Lyme arthritis or acrodermatitis chronic atrophicans (ACA) (Aucott et al., 2009; Bernard et al., 2019; Gordillo-Perez et al., 2018; Stanek and Strle, 2018; Stanek et al., 2012; Steere et al., 2016; Verhaegh et al., 2017). Although ACA has been confirmed by culture or by PCR testing, it is not conventional to diagnose LB by direct detection of the Bbsl complex from clinical samples (Asbrink et al., 1984; Branda and Steere, 2021).
The burden of LB is well documented in Canada, the USA, and the European Union. In Canada, LD incidence increased between 2009 and 2019 from 0.4 to 7.0 per 100,000 population per year (PPY) (Public Health Agency of Canada, 2022), which represented 2,634 LD cases in 2019. Using U.S. commercial insurance claims for LD, where similar diagnosis and treatment had been applied, there was an increase from 329,000 in 2005–2010 to 476,000 in 2010–2018 in the estimated number of annual patients (Kugeler et al., 2021). European national surveillance systems overall report approximately 129,000 LB cases each year, with the countries of highest incidence (>100 cases per 100,000 PPY) being Estonia, Lithuania, Slovenia, and Switzerland (Burn et al., 2023b).
Most LB diagnoses are verified by serology, and accurate serology testing should avoid false-positive results (Steere et al., 2016; Wilske et al., 2007). As single-tier immunoassays vary by sensitivity and specificity, a two-tier test (TTT) method of enzyme immunoassay followed by immunoblot, which can be standard (standard-TTT) or modified (modified-TTT), is preferred for LB diagnosis (Branda and Steere, 2021). The standard-TTT first tier measures total immunoglobulin by enzyme immunoassay (EIA), immunofluorescence assay (IFA), or whole-cell sonicate assay, which is followed in the second tier by Western blot (WB) using immunoglobulin M (IgM) or immunoglobulin G (IgG) immunoblots. IgM-based tests are more likely to yield false positives; hence, prominence is given to IgG TTT (Branda and Steere, 2021). The modified-TTT algorithm applies two or more first-tier EIA steps concurrently or sequentially, which enhances sensitivity while retaining specificity (Branda and Steere, 2021).
TTT is preferred in seroprevalence studies because studies using single-tier testing are prone to overestimation (Branda and Steere, 2021; Kodym et al., 2018). Furthermore, seroprevalence might not reflect ongoing Bbsl infections as antibody responses to infection can persist for up to two decades even after treatment and clinical resolution (Kalish et al., 2001). In Europe, it has been shown that seroprevalence ranged from 3.9% to 13.6% using TTT methods (Burn et al., 2023a). Seroprevalence varied by geography, and the weighted mean values were greater in Western (13.6%) and Eastern (11.1%) Europe compared with Northern (4.2%) and Southern (3.9%) Europe. Furthermore, weighted mean seroprevalence estimates for Europe were 40.6% among groups with higher risk compared to 3.9% in the general population considered to be at low risk of exposure to Bbsl-infected ticks (Burn et al., 2023a). From a systematic literature review of all published seroprevalence reports in China, seropositivity also varied by geography, being greatest in the northeastern and western provinces. Analysis demonstrated a 9.1% seropositivity by single-tier testing, but 1.8% among TTT studies; in the single-tier testing results, seroprevalence could be shown to vary by risk of exposure, 10.0% among high-risk and 4.5% among low-risk populations (Stark et al., 2022).
As climate change generates increasing average temperatures, with periods of greater humidity and more rainfall, the environment becomes more favorable for tick survival—resulting in increasing tick abundance, density, expansion, and distribution, along with evolution of tick species and pathogen genospecies. These habitat modifications drive enhanced tick activity during peak seasons, while greater tick exposure in endemic areas augments Bbsl transmission from animal hosts to humans (Bouchard et al., 2019; Eisen et al., 2016; Gong et al., 2025). By geographic range, climate change could lead to expansion of Bbsl-infected ticks across upslope elevational ranges as well as poleward (Ogden et al., 2021). Mathematical modeling scenarios project spatial shifts in existing LB foci from temperature increases leading to creation of further ecological niches suitable for tick expansion (Voyiatzaki et al., 2022), which would lead to greater control costs from rising LB cases (Choi and Lee, 2025). Surveillance of Bbsl-infected ticks to monitor current burden and detect emerging trends is key (Bouchard et al., 2019).
To understand LB burden beyond North America (Canada, USA), the European Union, and China—in particular, based on published literature from countries in the WHO regions of the Americas (i.e., Caribbean, México, and South America), Eastern Mediterranean, Europe, South-East Asia, and Western Pacific—we documented human LB epidemiology (cases, incidence, and seroprevalence) and Bbsl-infected tick frequencies (tick species, life stages, and Bbsl-infected proportions).
Materials and Methods
The systematic review protocol methodology, search strategy, and inclusion and exclusion criteria were developed by the authors (PROSPERO, CRD42021236906) based on the Preferred Reporting Items for Systematic Reviews and Meta-Analyses guidelines (Page et al., 2021).
Search strategy
This multidatabase systematic review (PubMed, EMBASE, and CABI Direct [Global Health]) covered from January 1, 2005 to July 1, 2022, subsequently updating the literature from PubMed up to 2024. Search terms were Lyme, Borrelia, and Borreliosis, with no limits on language, but excluding North America (Canada, USA), the European Union countries, and China. Review publications were scanned for references. Websites of government public health agencies and institutes, without limits on publication language, were searched (Supplementary Tables S1 and S2). This article focused on LB cases, incidence, and seroprevalence (from 2005 to 2022) and the proportion of vector-competent tick species infected with clinically relevant Bbsl complex genospecies (from 2010 to 2022). Non-English publications or reports were translated using DeepL (DeepL, 2022), engaging colleagues who were fluent or native speakers to elaborate translation accuracy. From some countries, local epidemiology was available in restricted-circulation journals or accessible from hospital or clinic reports (Colunga-Salas et al., 2020). All citations were merged and deduplicated. Screening selection of titles, abstracts, and full-text publications based on predefined inclusion and exclusion criteria was conducted independently by two reviewers (see subsections Inclusion criteria and Exclusion criteria). (The June 2022–December 2024 PubMed extended/updated search used the same three search teams, but screening selection did not use a double reviewer.)
Inclusion criteria
LB publications and surveillance reports included any case definition and any clinical manifestation; the cases could be clinical only or clinical with laboratory confirmation. Cases or incidence were only retained if the Bbsl-infection serological testing results provided both a numerator (number of seropositive) and denominator (size of population evaluated). Diagnostic single-tier testing or TTT could be based on EIA or IFA, then WB. For sequential seroprevalence estimates reported over time, the first value only was retained. Included tick surveillance studies (2010–2022) collected and tested at least one of these clinically relevant Bbsl genospecies: Bbss, B. afzelii, B. garinii (including closely related B. bavariensis), and B. spielmanii, as well as B. bissettiae, B. kurtenbachii, B. lusitaniae, B. mayonii, and B. valaisiana (Eisen, 2020). Ixodes for Bbsl-vector genospecies testing (via conventional PCR methods) included the following: I. scapularis, I. pacificus, I. ricinus, and I. persulcatus. Passive or active tick collection methods were used: passive through indirect collection by public citizen scientists of ticks from human or animal (domestic or wild) host source; active through dragging/flagging of host-seeking “questing” ticks (Eisen and Paddock, 2021). Bbsl prevalence was determined individually as the proportion of ticks with Bbsl infection or was assessed by a minimum infection rate (MIR) of pools of ticks, which is the number of positive pools over the total number of ticks tested (Raileanu et al., 2020). The flow of all information through our systematic review is presented in Fig. 1.
Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) flow diagram depicting the total number of analyzed publications, including those related to LB seroprevalence or infected tick proportions, of our systematic review. Adapted from Page et al, 2021. All publications identified via databases and registries (left column) were assessed for Lyme borreliosis (LB) cases and/or incidence, LB seroprevalence, and Borrelia burgdorferi sensu lato-infected ticks. Those identified via other methods (right column) were supplementary; surveillance data were assessed from public health institute/agency websites for reports of LB cases and/or incidence.
Exclusion criteria
We excluded health-economic or cost studies, case studies (including disease management or diagnostic guidelines), biomedical mechanisms, modeling or simulation, and animal studies. Published evidence only available in abstract form was excluded, as well as perspectives, letters, opinion articles, commentaries, and conference proceedings. Incidence results from publications were excluded if duplicating public health surveillance reports already analyzed in our review (Fig. 1).
Data extraction, synthesis, and analysis
Predefined outcomes of interest for extraction were as follows: (1) LB cases or incidence among defined populations; (2) seroprevalence diagnostic strategy and testing method, with seropositivity estimated from ≥1 serological test; (3) seroprevalence in lower- or higher-risk of tick exposure groups (Table 1); and (4) proportion of Bbsl infection among vector-competent ticks, including surveillance approach and testing method for tick species, life stage, and Bbsl genospecies. Numerical results were rounded to a first decimal point level of precision. Results were reported by the WHO region (Table 2) (World Health Organization, 2022).
Seroprevalence Study Cohorts by Population-Level Likelihood of Tick Exposure
WHO Regions for Countries with Information Available
Incidence trends were plotted with Excel (Fig. 2). Mean incidence calculation by the F-distribution method (Waller et al., 1994) used country-level surveillance and census data (e-Stat, 2022; KOSIS, 2016; Wikipedia, 2023) (Supplementary Table S3). Statistical analyses used the software R (R Core Team, 2023). Seroprevalence was synthesized from studies measuring IgM or IgG that used either single-tier testing or TTT, but TTT diagnostic strategies provide optimal sensitivity and specificity. The algorithm methodology to calculate overall TTT results was based on the original denominator, an interpretation consistent with recent publications (Branda and Steere, 2021; Burn et al., 2023a). We organized seroprevalence results based on residence or occupation criteria for likelihood of tick exposure (Burn et al., 2023a) (Table 1). Blood donors were inferred to be healthy, belonging to a low-risk population (even if authors did not report geospatial data).
Lyme borreliosis (LB) incidence in Japan, Russia, and South Korea from surveillance data (2005–2021)a. aBased on available surveillance reports.
Disease burden studies assessed quality based on design, case definitions, sampling methodology, diagnostic testing strategies, and sample size (Table 3 and Supplementary Table S3). I2 statistic heterogeneity (I2 > 70%) excluded data pooling and meta-analysis (Campbell et al., 2020; Deeks et al., 2022; Higgins et al., 2003; Imrey, 2020).
Results
Publications and countries
This systematic review captured 62 publications from 13 countries plus 41 surveillance reports from three of these countries. Among the publications, 17 reported LB cases, four estimated incidence, 25 reported seroprevalence, and 18 described proportion of Bbsl-infected ticks. One publication reported both LB case numbers and seroprevalence results; one study reported cases and tick data; and one study reported LB cases, incidence, and tick data (Fig. 1). By WHO region, 34 publications were from Europe, 12 from the Americas, 11 from Western Pacific, three from South-East Asia, and two from the Eastern Mediterranean (Fig. 3). As noted in the section Materials and Methods, there was substantial heterogeneity (I2 > 70%) in study populations, designs, case definitions, diagnostic and testing strategies, and tick collection methods (Tables 3 and 4; Supplementary Tables S4, S5, S6, and S7; and Fig. 2) that restricts comparability across studies or between countries, limiting interpretations (Ahaduzzaman, 2019; Campbell et al., 2020).
Number of publications, by WHO region, published between 2005 and 2022.
Number of Cases of Lyme Borreliosis and Incidence of Lyme Borreliosis by WHO Region and Country from Surveillance Data (2005–2021) and Publications Between 2005 and 2022
This table summarizes the available data. Data should not be interpreted solely based on this summary table but should be supplemented with the detailed data available in Supplementary Tables S4 and S5.
Data for Lyme borreliosis cases are presented per publication due to variability in study parameters. Data for Lyme borreliosis incidence are presented per geographical region, separately for surveillance or publication sources where applicable.
Three incidence estimates originated from surveillance data (2005–2021), while other data in this table were reported in publications.
ADEM, acute disseminated encephalomyelitis; GBS, Guillain–Barré Syndrome; LB, Lyme borreliosis; LNB, Lyme neuroborreliosis; NA, not available; PPY, population per year; WHO, the World Health Organization.
Outcomes
LB cases or incidence
Nineteen publications (eight countries) reported 2,015 LB cases (Table 3 and Supplementary Table S4). LB cases were reported from all the WHO regions except for the Eastern Mediterranean (Table 2), and national-level, public health surveillance from Europe (Russian Federation) and Western Pacific (Japan and South Korea) provided population-based LB incidence (Table 3; Supplementary Table S3, S5; and Fig. 2) available through national websites (Supplementary Tables S1 and S2). Furthermore, four publications from WHO Europe region (Russian Federation) reported population-based LB incidence (Table 3 and Supplementary Table S5).
Seroprevalence of antibodies to Bbsl infection
Of the 26 seroprevalence publications (11 countries) stratified by likelihood of tick exposure, low-risk populations accounted for 11 studies, high-risk populations for 10 studies, and five publications included both (Table 4 and Supplementary Table S6). TTT results (seroprevalence) were from low-risk populations in Brazil (6.2%), Colombia (4.6%), México (23.1%), Türkiye (0–14.5%), and Mongolia (0–14%), as well as from high-risk populations in Brazil (1.0–4.6%), Türkiye (0.9–15.8%), and India (0.4–3.0%) (Table 4 and Supplementary Table S6).
Descriptive Summary of Ixodes Surveillance and Borrelia burgdorferi sensu lato Infection Prevalence Data and Seroprevalence (Antibodies to Borrelia burgdorferi sensu lato) Estimates by WHO Region and Country from Publications Between 2005 and 2022
This table summarizes the available data. Data should not be interpreted solely based on this summary table, but should be supplemented with the detailed data available in Supplementary Tables S6–S8.
The vector-competent Ixodes species I. scapularis, I. pacificus, I. ricinus, and I. persulcatus were included in this systematic review.
Bbsl, Borrelia burgdorferi sensu lato; NA, not available; WHO, the World Health Organization.
Tick surveillance
Among 20 tick surveillance studies in six countries, two studies used passive surveillance (591 I. persulcatus ticks documented), while 18 studies applied active surveillance (35 I. scapularis, 738 I. ricinus, and 8,796 I. persulcatus documented) (Table 4 and Supplementary Tables S7, S8). From greatest to smallest, the proportion of Bbsl-infected Ixodes ticks was as follows: Europe—Russian Federation (80.4%), Western Pacific—Mongolia (49.7%), the Americas—México (34.2%), Western Pacific—Japan (25.5%), and Europe—Türkiye (19.9%) (Table 4; Supplementary Tables S7, S8; and Fig. 4). A 2022 review of the Bbsl prevalence in Ixodes ticks presented values that were as follows: greatest in Western Pacific—Malaysia (46.2%) and Europe—Russian Federation [Siberia] (28.8%); intermediate in Western Pacific—Mongolia (14.5%) and Japan (9.6%); and smallest in Western Pacific—South Korea (6.6%), South-East Asia—Pakistan (6.4%) and Thailand (4.1%), and Europe—Türkiye (2.8%) (Ji et al., 2022).
Summary of Ixodes surveillance and Borrelia burgdorferi sensu lato (Bbsl) infection prevalence data by WHO region and country from studies published between 2010 and 2022. B. Borrelia; B. burgdorferi sl, Borrelia burgdorferi sensu lato. aThe countries in dark gray are those with Lyme borreliosis publications/reports included in this systematic review, but for which no information on infected tick proportions was available: the Americas—Brazil, Colombia, and Cuba; Eastern Mediterranean—Jordan; South-East Asia—India; and Western Pacific—Malaysia and South Korea. This figure summarizes the available data. Data should not be interpreted solely based on this summary figure but should be supplemented with the detailed data available in Supplementary Tables S7 and S8.
WHO region
The Americas
Two studies in Brazil identified LB cases, one using a clinical case definition (Bonoldi et al., 2021) and another with laboratory confirmation (Naka et al., 2008) (Table 3 and Supplementary Table S4), although there is also the Brazilian LD-like illness, Baggio–Yoshinari Syndrome (BYS), that mimics LB even though Ixodes ticks do not transmit BYS (Yoshinari et al., 2022). LB was reported among farmers of Peru (Cervantes, 2018) and Colombia (Miranda et al., 2009), in the Piura and Amazonas subregions of Peru (Glenny et al., 2004), as well as in rural Tarja, Bolivia (Briançon Ayo, 2003). From México, one study in México City reported that 12.0% (23/191) of hospitalized patients with facial palsy were laboratory-confirmed LB (Gordillo-Perez et al., 2017; Gordillo-Perez et al., 2018). A second, nationwide study of hospitalized patients with neurological manifestations showed that 27.7% (168/606) were diagnosed as LNB via antibody testing of blood and cerebrospinal fluid (Gordillo-Perez et al., 2017; Gordillo-Perez et al., 2018) (Table 3 and Supplementary Table S4). Neither study confirmed travel histories among respective patient cohorts. Mexican investigators reported a standard-TTT 23.1% Bbsl antibody seroprevalence among older adults with mild cognitive impairment, although convenience sampling was limited by a small number (n = 39) of cases (Herrera-Landero et al, 2019; Passos et al, 2009) (Table 4 and Supplementary Table S6). Colunga-Salas et al. (2020) reviewed 398 LB cases between 1939 and 2020 in México. While acknowledging the limitations of serologic testing, not isolates, to identify genospecies, 35.6% of the cases could be attributed to Bbsl (Bbss [n = 128], B. garinii [n = 10], or B. afzelii [n = 2]) (Colunga-Salas et al., 2020). Details are presented for the LB cases (Supplementary Table S9) and for Bbsl detection in mammalian hosts (Supplementary Table S10). LB incidence has not been estimated in the Americas.
In Brazil, there was a standard-TTT seroprevalence value of 6.2% of Bbsl antibodies documented among low-risk populations (Passos et al., 2009), whereas for high-risk populations, the standard-TTT seroprevalence values were 1.0% (Goncalves et al., 2013) and 4.6% (Nascimento et al., 2016). In Colombia, nationwide standard-TTT seroprevalence of antibodies to Bbsl in high-risk groups was 4.6% (Miranda et al., 2009) (Table 4 and Supplementary Table S6). A recent study in Colombia identified Borrelia in ticks feeding from domestic or wild animals in the Orinoquia region (Ossa-Lopez et al., 2024). In South American countries, Bbsl genospecies such as B. chilensis, for which human pathogenicity is unknown, were found in the suspected vector I. stilesi both during host-seeking and while blood feeding on rodents and deer (Cervantes, 2018; Ivanova et al., 2014; Robles et al., 2018). Recently proposed Bbsl vectors in Argentina are I. pararicinus and I. affinis (Lucca et al., 2024). Further genetic- and microbiological-based vector surveys are necessary to establish any clinical implication of these Ixodes species in LB (Ivanova et al., 2014). (Passos et al., 2009). One tick surveillance study in northeast México identified 35 I. scapularis (life stage NR) using active surveillance (tick dragging among vegetation and mammalian trapping among wild animals) across four sites to model LB risk (Feria-Arroyo et al., 2014). Bbsl infection prevalence among the collected ticks was reported in aggregate, giving a pooled Bbsl infection prevalence of 34.3% (Feria-Arroyo et al., 2014) (Table 4; Supplementary Tables S7, S8; and Fig. 4); however, data-quality issues have been raised about possible laboratory PCR contamination (Norris et al., 2014; Norris et al., 2015), and the reported Bbsl-infected tick prevalence was larger than surveillance results from the southeastern USA (Lehane et al., 2021).
Eastern Mediterranean
There were no published LB cases or LB incidence published for Eastern Mediterranean countries.
For tick surveillance, in Iran, a 0.9% infection of Borrelia (not specified by Bbsl genospecies) among I. ricinus was identified by PCR; additional analysis revealed both Borrelia and the relapsing fever spirochete Borrelia miyamotoi (Naddaf et al., 2020) (Table 4; Supplementary Tables S7, S8; Fig. 4). A 2023 review of North Africa indicated I. ricinus presence in Algeria, Morocco, and Tunisia, but status is unknown for Egypt and Libya (Kahl and Gray, 2023). Among I. ricinus ticks in North Africa, Bbsl and B. garinii, as well as B. lusitaniae, infection has been documented (Koutantou et al., 2024; Perveen et al., 2021; Trevisan et al., 2021).
Europe
Most LB case report studies were from the Russian Federation subnational areas: six applied laboratory confirmation (Table 3 and Supplementary Table S4), and four also estimated LB incidence (Table 3 and Supplementary Table S5). The yearly incidence ranged 2.7–7.0 per 100,000 PPY throughout 2009–2019, decreasing to 2.86 in 2020 and to 2.65 in 2021 (Fig. 2; Supplementary Table S3). The Russian Federation national incidence was 9.9 per 100,000 PPY (1997–2015) (Dedkov et al., 2017). Mean incidence could be estimated at 4.8 per 100,000 PPY (95% confidence interval [CI]: 4.7–4.9) (see subsection Data extraction, synthesis, and analysis for details), evaluated by subnational area values that ranged from 0.2–0.8 in the Komi Republic (1997–2017) to 40.5 in Altai (1997–2015) (Table 3, Supplementary Table S5). One incidence value resulted from a study to demonstrate tick elimination effectiveness of Baytex, but case definitions were unreported and methodology unclear (Bogachkina et al., 2011). While some subnational area LB incidence values are lower than those of Europe (Burn et al., 2023a), the Russian Federation could be classified a “high-incidence LB area” as per the U.S. Centers for Disease Control and Prevention national surveillance guidelines (Centers for Disease Control and Prevention, 2020; Eisen, 2020; Eisen and Paddock, 2021) that define a high-incidence U.S. state as >10 LB cases per 100,000 PPY (Schwartz et al., 2017). One national-level study in Türkiye investigated pediatric LNB case records (Celik et al., 2016a; Celik et al., 2016b) (Table 3 and Supplementary Table S4). Önal et al. compiled 75 LB cases between 2000 and 2018; although not all cases were WB confirmed, the authors proposed that LB could be an important health care problem in Türkiye (Onal et al., 2019). By contrast, a recent emergency department diagnostic follow-up, applying both clinical and laboratory criteria, reported only one LB case among 69 patients with tick contact in Bolu Province, Türkiye (Arslan et al., 2024). A 2021 review among 15 Eastern Mediterranean countries included LB among the zoonotic bacterial tick-borne diseases studied. In Türkiye, there were seven LNB cases confirmed by TTT (enzyme-linked immunosorbent assay [ELISA] and WB); however, for the one LB case report from Iraq and another LB case in Saudi Arabia, there could have been either travel-related encounters in endemic areas such as Europe or a lack of assay specificity due to cross-reactivity between Borrelia genospecies (Behzadi et al., 2021).
There was no published TTT seroprevalence of antibodies to Bbsl infection from Russia (Table 4 and Supplementary Table S6). Five low-risk population studies in Türkiye confirmed 0–14.5% standard-TTT seroprevalence (Bucak et al., 2016; Çelik et al., 2020; Cora et al., 2017; Kaya et al., 2008) and 2.5% seroprevalence by modified-TTT (Uyanık et al., 2009) (Table 4, Supplementary Table S6). Among six high-risk population studies in Türkiye, a standard-TTT seroprevalence range of 0.9–6.2% (Uyanık et al., 2009) and a 2.0% modified-TTT seroprevalence were identified (Akar et al., 2019; Aslan Basbulut et al., 2012; Cikman et al., 2019; Kaya et al., 2008; Parlak et al., 2015). The study by Parlak et al., for instance, applied sample randomization, results stratified by sex, a comprehensive statistical analysis, and guideline-based diagnostic methods (ELISA followed by a confirmatory WB) (Parlak et al., 2015).
Ten tick surveillance studies (i.e., one passive, eight active, and one NR) from the Russian Federation revealed variations of life stage (Bbsl-infected proportion) among I. ricinus from nymphs (27.3%), nymphs/adults (33.4%), to adults/NR (9.8–80.4%) and I. persulcatus from adults/NR (12.0–75.3%) (Dedkov et al., 2017; Khasnatinov et al., 2016; Lubova et al., 2020; Melnikova et al., 2021; Morozova et al., 2011; Movila et al., 2014; Mukhacheva and Kovalev, 2014; Shutikova et al., 2020) (Table 4; Supplementary Table S7, S8; and Fig. 4). Genospecies isolated from I. persulcatus ticks were B. afzelii, B. bavariensis, and B. garinii (Morozova et al., 2011; Mukhacheva and Kovalev, 2014) (Supplementary Tables S7, S8 and Fig. 4). In Türkiye, the Bbsl-infected tick proportion of I. ricinus was 19.9% (adults/NR) (Sen et al., 2011). Also, 6.5–41.7% of I. ricinus was infected with Bbsl complex, a frequency by genospecies of 1.6–12.5% B. garinii and 1.6–7.3% B. afzelii; nevertheless, B. lusitaniae was the most frequent genospecies, infecting between 4.8% and 25.0% of I. ricinus, and there was 1.6–5.9% B. valaisiana documented (Kar et al., 2013; Polat et al., 2021; Sen et al., 2011) (Table 4; Supplementary Tables S7, S8; and Fig. 4).
South-East Asia
In north Haryana, India, positive anti-Borrelia antibodies were documented among patients with erythema migrans (Jairath et al., 2014). Vinayaraj et al. (2021) conducted a 3-year, cross-sectional investigation that provided a detailed case definition with comprehensive description of laboratory methods and statistical analysis, adding to cases of LB in India described elsewhere (Negi et al., 2021), to confirm 18 LB or LNB cases from 252 suspected at the Indian national level and to indicate that none of the confirmed cases “had visited or traveled to any foreign countries endemic for LB” (Vinayaraj et al., 2021) (Table 3 and Supplementary Table S4). No South-East Asia incidence estimates could be identified. One Indian study indicated 0.4–3.0% TTT seroprevalence among forest workers and staff in the Rajiv Gandhi National Park region of the Nagarahole and Bandipur mountain ranges in southern India (Babu et al., 2020) (Table 4 and Supplementary Table S6). Although this rate of seropositivity might suggest Bbsl infection in India, the 98–99% specificity typical of the assay could explain some false positives. Recently, in Sikkim and Arunachal Pradesh, there was a 3.7% (95% CI: 2.4–5.2%) single-tier test seroprevalence, adjusted for sensitivity and specificity of IgG ELISA kits, among study participants with history of tick bite or clinical LB (Tilak et al., 2024). There was no published tick surveillance from South-East Asia.
Western Pacific
There was one clinical LB study from Mongolia (von Fricken et al., 2019) and two studies of laboratory-confirmed LB cases in South Korea (Moon et al., 2015; Park et al., 2011). In Japan and South Korea there are mandatory national public health surveillance of cases, confirmed by clinical presentation and laboratory results (Supplementary Table S1). Japan notified 5–27 LB cases annually (2006–2021), and South Korea 2–31 cases each year (2011–2021) (Fig. 2 and Supplementary Table S3). Incidence per 100,000 PPY was 0.01–0.02 in Japan and 0.0–0.06 in South Korea (Fig. 2 and Supplementary Table S3), with a yearly increase over the surveillance period. Mean LB incidence could be estimated to be 0.01 (95% CI: 0.01–0.02) in Japan and 0.03 (95% CI: 0.02–0.05) in South Korea (see Data Extraction, Synthesis, and Analysis section for details) (Fig. 2 and Table 3). Only Mongolia reported seroprevalence based on standard-TTT among low-risk populations that varied by subnational area, with values of 1.9% (Selenge), 3.0% (Bulgan and Tov/Ulaanbaatar), and 14.0% (Dornogovi)—but there were no other positive serology samples from the remaining regions of the country (Walder et al., 2006) (Table 4, Supplementary Table S6). For ticks, there were five I. persulcatus surveillance studies: two from Japan, two from Mongolia, and one encompassing both countries (Table 4; Supplementary Tables S7, S8; and Fig. 4); two of the studies reported both nymph and adult life stage (Lagunova et al., 2022; Okado et al., 2021), whereas three reported uniquely adult life stage (Iwabu-Itoh et al., 2017; Scholz et al., 2013; Seto et al., 2021) (Table 4; Supplementary Tables S7, S8; and Fig. 4). In Japan, life stage (Bbsl-infected proportion) among I. persulcatus ranged from nymphs (0–10.0%), nymphs/adults (1.8–23.6%), and adults/NR (detected–25.5%) (Iwabu-Itoh et al., 2017; Okado et al., 2021; Seto et al., 2021). The proportions infected with Bbsl genospecies varied by Japan subnational area, up to 23.6% in Hokkaido where B. afzelii infected 1.8% while B. garinii (B. bavariensis) infected 21.8% of I. persulcatus (Okado et al., 2021) (Table 4; Supplementary Tables S7, S8; and Fig. 4). In Mongolia, the Bbsl infection by life stage (proportion) among I. persulcatus was nymphs (detected), nymphs/adults (49.4%), and adults (7.0–49.7%) (Iwabu-Itoh et al., 2017; Lagunova et al., 2022; Scholz et al., 2013). Prevalence of Bbsl infection of I. persulcatus varied by province in Mongolia from 17.0–47.8% in Selenge, 30.9% in Khuvsgul, and 41.9–49.2% in Bulgan (Iwabu-Itoh et al., 2017; Lagunova et al., 2022). A study in Selenge reported I. persulcatus infection by B. afzelii (7.0%) and B. bavariensis (18.8%) (Scholz et al., 2013) (Supplementary Table S8).
Discussion
Cases, seroprevalence, and infected tick distribution suggest that an LB burden exists beyond North America (Canada, USA), the European Union countries, and China. Nonetheless, substantial heterogeneity in the reviewed 62 publications (as well as potentially in the 41 surveillance reports)—by design, populations, study period, sample size, diagnostic strategies, testing methods, tick surveillance, or reporting systems—would hamper interpretation and constrain comparison of the evidence between the 13 countries analyzed in this systematic review. For example, LB cases without a recorded travel history could be due to a tick exposure infection from an endemic region outside the reporting country, or the single-tier test favored in many seroprevalence studies could be prone to false-positive results. From 26 seroprevalence studies indicating Bbsl-infected tick exposure, there was seroprevalence reported from 11 of 13 countries (except Iran and Japan). For TTT results only, there was a 0–23.1% seroprevalence range reported across six countries: 1.0–6.2% in the Americas—Brazil, 4.6% in —Colombia, and 23.1% in —México; 0–15.8% in Europe—Türkiye; 0.4–3.0% in South-East Asia—India; and 0–14% in Western Pacific—Mongolia (Table 4 and Supplementary Table S6). Seropositivity could be overestimated: values might fall within the false-positive rate for the serology test, while lower prior probability would suggest that seropositive samples are more likely to be false positives than true positives. Furthermore, single-tier assay positive results do not constitute conclusive evidence of Bbsl infection, as cross-reactivity can occur with relapsing fever Borrelia (Ivanova et al., 2014; Robles et al., 2018), and any individual Borrelia serology result could be from genospecies that are not Bbsl (Grazlewska and Holec-Gasior, 2023; Wojciechowska-Koszko et al., 2011). Nonetheless, Bbsl antibody seropositivity, measured in individuals bitten by Bbsl-infected ticks or among those presenting with clinical signs and symptoms, is suggestive of LB (Hammers-Berggren et al., 1994).
There were 20 Bbsl-infected Ixodes tick studies in the Americas—México, Eastern Mediterranean—Iran, Europe—Russian Federation and Türkiye, and Western Pacific—Japan and Mongolia (Table 4; Supplementary Table S7; and Fig. 4). Tick surveillance in a setting reveals a potential LB risk by suggesting patterns or trends in the distribution, abundance, and stability of both tick species and their vectored pathogens (Guillot et al., 2020; van den Wijngaard et al., 2017). In our systematic review, most studies (18/20) used active methods such as dragging and flagging to estimate tick densities (tick population dynamics), infection prevalence (stability of pathogen infections in ecological communities), and phenology (peak-seasonality of questing ticks). Passive surveillance, used by only a few (2/20) studies (Shutikova et al., 2020), is a sensitive and cost-effective method to determine the presence of tick species and their associated pathogens across large geographic settings that provides trends in proportional abundances across tick vectors over time in an area, although inherent biases include public awareness, transportation history, sample integrity, laboratory testing methods, and geolocation precision (Centers for Disease Control and Prevention, 2020; Eisen, 2020; Eisen and Paddock, 2021).
Tick sampling methods designed to document LB burden can be incomplete, and habitat, level of urbanization, and season can influence the proportion of Bbsl-infected ticks (Hansford et al., 2022). Routinely assessing LB risk among populations requires monitoring the presence of Bbsl among vector ticks and establishing the proportion of infected ticks (Eisen and Paddock, 2021; Fleshman et al., 2021; Guillot et al., 2020; Millins et al., 2021; Porter et al., 2021). For instance, some tick studies in our review used the MIR method to measure Bbsl infection. The MIR method is based on the number and size of pools tested; moreover, it assumes that the positive pool contains only one infected tick. This could be useful in a smaller sample size; however, this method does not estimate actual infection prevalence, which precludes accurate interpretation of the estimated proportion of collected ticks infected with Bbsl. Rather, MIR only measures the lower bound, which would lead to underestimation whenever infection prevalence is high or the pool size is large. Hence, studies that used this method might have underestimated tick infection rates (Estrada-Pena et al., 2021; Raileanu et al., 2020). Other factors to explain potential differences include the tick species and life stage, as well as the PCR detection method specificity for Bbsl genospecies. For example, one study in Japan (Yamagata Prefecture) did not use a Bbsl genospecies-specific molecular detection method and could only detect the Bbsl complex in nine I. persulcatus among 164 ticks collected (Seto et al., 2021). In addition, while Bbsl infection can manifest as LB, not all tick exposures result in clinical disease (Hammers-Berggren et al., 1994). Therefore, publications should clearly describe the methodologies used, as harmonization of tick surveillance program methods ideally would yield the most exact and replicable information with bias reduction to allow for interpretation across different studies and analyses (Eisen and Paddock, 2021).
Challenges remain in LB surveillance. While standardized detection methods are essential, recent reviews have found substantial heterogeneity by LB case definitions, serological testing methods, and the type of system in place—limiting comparative interpretations at a global level (Burn et al., 2023b; Nagarajan et al., 2023). While efforts have been made in Europe to standardize case definitions (European Center for Disease Prevention and Control, 2018; European Commission, 2018), and in some countries reporting LB cases is notifiable and a part of national surveillance systems (Canada Government: Public Health Services, 2025; Centers for Disease Control and Prevention, 2022; European Center for Disease Prevention and Control, 2018), momentous challenges remain in disease awareness, communication, reporting, and alignment on common indicators for surveillance (Blanchard et al., 2022; Kugeler et al., 2024). Even when established surveillance systems are in place, gaps in collecting vital public health information remain (Mead et al., 2024). Furthermore, countries where LB could be emerging still have not established disease reporting systems to capture LB as part of their infectious disease surveillance framework. As technology advances, other data sources such as electronic health records present opportunities to be leveraged as sources of clinical information to address some of these surveillance challenges (Mead et al., 2024). In LB burden, seroprevalence is often the primary indicator although diagnostic methods are not standardized (Branda and Steere, 2021; Perronne, 2014). Nonetheless, robust surveillance systems will be vital to monitor disease trends, to identify areas where there is a LB burden, and to document the impact of prevention measures such as potentially vaccines (Burn et al., 2023b; Mead et al., 2024). Our review, among geographic areas typically neither studied nor highlighted for LB, provides notable evidence of this public health threat being present within countries and possibly beyond national borders.
Conclusions
This systematic review builds upon available national evidence in 13 countries of LB cases, seroprevalence, or Bbsl-infected vector-competent ticks outside of North America (Canada, USA), the European Union countries, and China; nonetheless, providing a comprehensive overview of the epidemiology of LB across five WHO regions—the Americas, Eastern Mediterranean, Europe, South-East Asia, and Western Pacific—is intricate, particularly as LB serological testing for diagnosis and the methods for tick surveillance are not homogeneous. LB burden documentation remains a challenge because there are uncertainties, whether based on lack of travel histories for LB cases, potential for cross-reactivity of serological tests, or absence of confirmation of key vector-competent ticks for Bbsl transmission. Partial indications of LB burden—by cases, seroprevalence, or tick distribution—are available within some of the countries of the WHO regions of the Americas (Brazil, Colombia, Cuba, and México), Eastern Mediterranean (Iran and Jordan), South-East Asia (India), and Western Pacific (Malaysia). By contrast, in Europe (Russian Federation and Türkiye), along with other countries of Western Pacific (Japan, Korea, and Mongolia), there is consistent evidence of LB cases, incidence, and seroprevalence, as well as of Ixodes tick species infected with and capable of transmitting the Bbsl genospecies that cause LB. Continuing LB epidemiology and tick surveillance could identify settings within the Russian Federation and Türkiye, as well as within Japan, Korea, and Mongolia, where disease risk indicates the introduction of LB prevention strategies, while their neighboring countries in the European and Western Pacific WHO regions should consider initiating LB cases or incidence, Bbsl antibody seroprevalence, and Bbsl-infected tick surveillance research.
Authors’ Contributions
L.B.: Conceptualization, methodology, investigation, design, validation, analysis, data curation, data extraction, visualization, writing—original draft, project administration, and supervision. M.A.F.: Conceptualization, methodology, design, visualization, writing—review and editing, project administration, funding, and supervision. J.M.: Methodology, validation, data curation, data extraction, analysis, visualization, and writing—original draft. C.J.G.: Conceptualization and writing—review and editing. A.D.: Writing—review and editing. P.H.K.: Methodology and writing—review and editing. J.H.S.: Conceptualization, methodology, design, writing—review and editing, project administration, and supervision.
Footnotes
Acknowledgments
The authors thank Aura Victoria Gutiérrez Rabá (Epidemiologist at P95) for her work extracting tick and seroprevalence data throughout this review. They also thank Thao Mai Phuong Tran (Statistician at P95) for her support in calculating incidence from the national public health surveillance data, and Lotte Mathé (Medical Writer at P95) for her professionalism. Medical colleagues from
Author Disclosure Statement
L.B. and J.M. declare no conflicts of interest. M.A.F., A.D., P.H.K., and J.H.S. are all employees of
Funding Information
This study was supported and jointly funded by Valneva and Pfizer as part of their codevelopment of a Lyme disease vaccine. They funded costs associated with the development and publication of the present article.
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References
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