The research, published in the journal Parasites & Vectors, was conducted by James C. Burtis, Erik Foster, and Rebecca J. Eisen of the CDC’s Division of Vector-Borne Diseases in Fort Collins, Colorado. Their central question was deceptively simple: across seven western states, which counties have environmental conditions suitable both for the bacterium to maintain itself in local wildlife cycles and for infected nymphs to climb up onto vegetation and wait for a host? That second condition matters enormously for human health. Nymphal ticks are tiny, roughly the size of a poppy seed, and their host-seeking behavior above the ground is what brings them into contact with people hiking, gardening, or working outdoors. A tick that never quests above vegetation poses far less risk of a bite.

To build their analysis, the team confronted the fundamental scarcity of western tick surveillance data. Systematic records documenting the densities of host-seeking, infected nymphs are limited in the region, in stark contrast to the eastern United States where such data underpin county-level risk maps. The researchers turned to the ArboNET Tick Module, a national database maintained by the CDC that aggregates tick surveillance submissions from public health partners. Because those records alone could not cover the full geographic extent of potential tick habitat, they supplemented the database with an exhaustive review of the published literature and public health records, collating county-level observations of host-seeking nymphs and separately compiling reports of B. burgdorferi sensu stricto infections detected in both nymphal and adult I. pacificus.

The compilation revealed a striking imbalance. Host-seeking I. pacificus nymphs had been recorded in 54 counties across the seven western states, while evidence of Bbss-infected I. pacificus existed in only 36 counties, all of them in California, Oregon, and Washington. That distinction is critical. A tick population can thrive in a county without the bacterium circulating among the wildlife that feed the ticks. Enzootic transmission, the sustained cycling of the spirochete between ticks and reservoir hosts such as small mammals and birds, requires a specific confluence of vector abundance, competent reservoir species, and favorable climate. Some counties may host abundant ticks but, for reasons of host community composition or microclimate, never sustain the pathogen.

With these records in hand, the researchers built separate habitat suitability models for the two phenomena: one predicting where host-seeking nymphs are likely to occur, and another predicting where Bbss-infected ticks of either stage have been or are likely to be found. The modeling approach drew on multiple algorithms rather than a single statistical technique, a strategy that guards against the idiosyncrasies of any one method. Crucially, the team set the suitability thresholds of all algorithms to achieve 90 percent sensitivity, meaning the models were deliberately tuned to flag nearly every county with a known record, even at the cost of including some counties where the tick or pathogen may ultimately be absent. In public health terms, this conservative choice favors caution: it is better to overestimate the map of potential risk than to tell residents of an affected county they are safe.

The final step was an overlay. By intersecting the suitable habitat for host-seeking nymphs with the suitable habitat for infected I. pacificus, the researchers identified counties where the environment plausibly supports the full combination of conditions that generate acarological risk: infected nymphs actively questing above vegetation. The resulting map told a geographically focused story. Suitable habitat for encountering Bbss-infected host-seeking nymphs clustered mostly in central and northern California and along the coastal corridors of Washington and Oregon. The pattern was markedly narrower than the overall footprint of the tick itself, confirming that I. pacificus occupies a far broader range than the Lyme disease transmission zones within it.

The numbers quantify that contrast vividly. An earlier modeling effort had classified 113 counties across the western states as suitable for I. pacificus. Yet the new analysis found only 76 counties characterized as suitable for detecting Bbss-infected host-seeking nymphs by at least one of the team’s models. In other words, more than a third of the counties that could host the tick lack evidence of conditions supporting the infected, questing nymphs that pose the greatest hazard to people. For residents and clinicians, this reframes the geography of concern: living in a county where western blacklegged ticks exist is not equivalent to living in a county where Lyme transmission cycles are plausible.

The study’s authors are careful about what their models can and cannot say. The suitability maps identify where infected, host-seeking nymphs are environmentally plausible, but they do not differentiate the magnitude of risk within or among counties. A county flagged as suitable might support low densities of infected nymphs while another supports densities orders of magnitude higher, and the binary classification cannot capture that gradient. Nor can the models replace direct measurement; density of infected nymphs, the metric most tightly linked to human case risk, requires labor-intensive field dragging and pathogen testing that surveillance programs in the West have struggled to sustain. What the models provide instead is a prioritization tool, a way to direct scarce surveillance resources toward the counties where field data would be most informative.

That prioritization is precisely how the authors frame the study’s practical payoff. As a next step toward improving acarological risk assessment in the western United States, the research highlights specific counties where enhanced tick surveillance is warranted. Field confirmation in modeled-suitable counties without existing records could verify the presence of infected questing nymphs, while surveillance in borderline counties could sharpen the thresholds of future models. The approach mirrors strategies used in the East, where layered surveillance and modeling have produced the county maps that clinicians and the public routinely consult. Bringing the West closer to that standard has been a long-standing goal of CDC vector-borne disease programs, and the intramurally funded study represents a substantial advance toward it.

For the public, the message embedded in the maps is one of informed vigilance rather than alarm. The core risk zones in central and northern coastal California and the Pacific Northwest coasts are places where outdoor recreation and residential development interleave with tick habitat, and where standard precautions remain essential: using repellents, performing tick checks after time outdoors, and promptly removing attached ticks. At the same time, the finding that infected questing nymphs are plausible in fewer counties than the tick’s total range offers reassurance to residents of inland and southern areas where the tick occurs but the pathogen apparently does not. As climate and land use continue to shift, the interplay between tick distributions and pathogen transmission will evolve, and models like these, anchored to surveillance and repeatedly updated, will be central to keeping western Lyme disease risk maps honest, current, and actionable.

Subject of Research: Habitat suitability modeling for Borrelia burgdorferi-infected western blacklegged tick nymphs in the western United States

Article Title: Identifying counties with suitable habitat for host-seeking Borrelia burgdorferi sensu stricto-infected Ixodes pacificus nymphs across seven states in the western United States

Article References: Burtis, J. C., Foster, E., & Eisen, R. J. (2026). Identifying counties with suitable habitat for host-seeking Borrelia burgdorferi sensu stricto-infected Ixodes pacificus nymphs across seven states in the western United States. Parasites & Vectors. https://doi.org/10.1186/s13071-026-07730-5

Image Credits: AI Generated

DOI: 10.1186/s13071-026-07730-5

Keywords: Lyme disease, Ixodes pacificus, Borrelia burgdorferi, tick surveillance, habitat suitability modeling, nymphal ticks, western United States, CDC, acarological risk, vector-borne disease, county-level mapping, Parasites & Vectors

Methylglyoxal is a small, electrophilic ketoaldehyde produced as a byproduct of carbohydrate metabolism. In many organisms it arises when the flow of sugar phosphates through central metabolism becomes imbalanced, particularly when dihydroxyacetone phosphate accumulates. The enzyme methylglyoxal synthase, encoded by the mgsA gene, channels this intermediate into methylglyoxal rather than allowing it to continue down the glycolytic route. Once formed, methylglyoxal attacks nucleophilic side chains on amino acids, most notably lysine, arginine, and cysteine residues, forming covalent adducts known as advanced glycation end products. These modifications can distort protein structure, interfere with enzyme active sites, and disrupt protein-protein interactions. Because of this destructive chemistry, the accumulation of methylglyoxal has been described as carbonyl stress, a condition generally assumed to be harmful or outright lethal to microbial cells.

The research team set out to determine whether this pathway even operates in spirochetes, a group of spiral-shaped bacteria with distinctive genetics and metabolism. B. burgdorferi has an unusually reduced genome and depends almost entirely on its tick and mammalian hosts for nutrients, so the question of how it manages carbohydrate and phosphate balance is biologically important. The investigators identified several environmental signals that trigger carbonyl stress in the Lyme disease spirochete, including glycerol and peptides. Glycerol is particularly interesting because B. burgdorferi can use it as a carbon source during its tick phase, when blood is unavailable and the bacterium must survive on alternative substrates. Peptides, meanwhile, reflect the amino acid-rich environment the spirochete encounters in mammalian tissues and blood. The finding that both classes of nutrients feed into the carbonyl stress pathway suggests that methylglyoxal production is tied to the specific metabolic states the bacterium passes through during its enzootic cycle between tick and host.

Central to the study was the demonstration that methylglyoxal production and the resulting glycation of proteins depend on the product of the mgsA gene, designated bb0364 in the B. burgdorferi genome. When this gene’s function was removed, the spirochete no longer produced detectable methylglyoxal, and the characteristic protein adducts of advanced glycation disappeared. This genetic dependency establishes that the pathway is not an incidental chemical side reaction but a controlled enzymatic process. The researchers could therefore treat mgsA as a molecular switch, turning carbonyl stress on or off and observing the consequences for the bacterium’s physiology and its ability to infect animals.

One of the most consequential discoveries was phylogenetic. The carbonyl stress pathway proved to be active in Lyme disease spirochetes but absent in function from relapsing fever Borrelia species and from B. mayonii, another human pathogen in the Lyme disease group. Relapsing fever spirochetes are famous for achieving enormous densities in the bloodstream, cycling through antigenic variation to evade antibodies and producing recurrent febrile episodes. The fact that these blood-dwelling relatives lack an active methylglyoxal pathway, while the tissue-adapted Lyme disease spirochete retains one, hints at an evolutionary trade-off. The authors suggest that carbonyl stress may be selected against in spirochetes that reach high numbers in the blood, where the metabolic consequences of glycation could become intolerable at large population sizes.

To test whether methylglyoxal production matters during actual infection, the team turned to the tick-mouse model of Lyme disease, the standard experimental system for studying B. burgdorferi in its natural transmission context. Ticks infected with spirochetes were allowed to feed on mice, and the course of infection was followed through the mammalian host. The results provided evidence that the production of methylglyoxal and the glycation of proteins are not necessarily lethal to the spirochete, at least in this organism, contradicting the long-standing assumption that carbonyl stress is uniformly toxic. Bacteria carrying an intact pathway persisted through the infection cycle, indicating that B. burgdorferi can tolerate a level of self-inflicted protein damage that would cripple many other microbes. This tolerance raises the possibility that the pathway confers some benefit that offsets its biochemical costs.

The clearest hint of that benefit came from an elegant cross-species experiment. The researchers introduced the B. burgdorferi mgsA gene and its associated carbonyl stress pathway into B. hermsii, a relapsing fever spirochete that naturally lacks the system. When the engineered bacteria were used to infect mice, the peak level of spirochetemia during the relapse phase of infection dropped significantly compared with infections caused by unmodified B. hermsii. In other words, forcing a blood-dwelling spirochete to run the Lyme disease carbonyl stress pathway curtailed its ability to flood the bloodstream. This result supports the idea that methylglyoxal production imposes a cost on explosive growth in blood, and it explains why relapsing fever species, which depend on high-density blood infections for transmission, would have lost or never maintained this pathway.

Taken together, these findings define a previously unrecognized post-translational modification system in B. burgdorferi. Rather than relying solely on the phosphorylation, acetylation, and proteolytic processing that bacteria typically use to tune protein function, the Lyme disease spirochete appears to exploit direct chemical glycation by methylglyoxal as a regulatory layer. Because the pathway is triggered by glycerol and peptides, nutrients encountered at particular stages of the tick-mouse cycle, methylglyoxal-mediated modification could help the bacterium reprogram its proteome as it transitions between metabolically distinct environments. Proteins damaged by glycation might be preferentially degraded, redirected, or inactivated, allowing the spirochete to adjust its physiology in ways that standard transcriptional regulation alone cannot achieve.

The study also reframes how scientists think about carbonyl stress in microbial pathogenesis. For decades, methylglyoxal has been studied mainly as a threat that bacteria must detoxify through glyoxalase systems and related enzymes. The new work shows that at least one pathogen has integrated this reactive metabolite into its normal biology, tolerating the damage it causes and possibly using it to govern its lifestyle. The contrast between Lyme disease and relapsing fever spirochetes offers a natural experiment in evolutionary strategy: one pathogen persists at low densities in collagen-rich tissues for months or years, while the other races through the blood in massive waves. The presence of an active carbonyl stress pathway in the former and its apparent incompatibility with the latter suggests that methylglyoxal biology is entwined with the fundamental ecological strategies of these bacteria.

Future work will need to identify which B. burgdorferi proteins are glycated in vivo, how those modifications alter protein function, and whether the pathway influences the bacterium’s ability to establish persistence in joints, heart, and nervous system tissue. The findings also raise questions about whether carbonyl stress contributes to the chronic inflammatory environment characteristic of Lyme disease, since advanced glycation end products are known to interact with host immune receptors in other contexts. For now, the study stands as a vivid example of how a molecule once dismissed as metabolic waste can turn out to be a purposeful instrument of pathogen regulation, and it underscores how much remains to be learned from comparing closely related spirochetes that have evolved to occupy radically different niches within their hosts.

Subject of Research: Methylglyoxal-mediated carbonyl stress and protein glycation regulation in Lyme disease and relapsing fever spirochetes

Article Title: Metabolic regulation of the carbonyl stress pathway and methylglyoxal in Lyme disease and relapsing fever spirochetes

Article References: Drecktrah, D., Hall, L. S., Cheff, B., Richards, C., Raffel, S. J., Wulf, M., Bailey, I. T., Gherardini, F., & Samuels, D. S. (2026). Metabolic regulation of the carbonyl stress pathway and methylglyoxal in Lyme disease and relapsing fever spirochetes. PLOS Pathogens, 22(9), e1014657. https://doi.org/10.1371/journal.ppat.1014657

Image Credits: AI Generated

DOI: 10.1371/journal.ppat.1014657

Keywords: Lyme disease, Borrelia burgdorferi, methylglyoxal, carbonyl stress, advanced glycation end products, mgsA, spirochetes, relapsing fever, Borrelia hermsii, protein glycation, tick-mouse model, metabolic regulation

The logic behind the approach rests on the peculiar ecology of Lyme disease in the northeastern United States. The blacklegged tick, Ixodes scapularis, passes the bacterium Borrelia burgdorferi sensu stricto through its life stages, but the pathogen’s persistence in a given landscape depends heavily on one particular host: the white-footed mouse, Peromyscus leucopus. These abundant rodents serve as the principal natural reservoir of the spirochete, and larval ticks that feed on infected mice are far more likely to acquire the bacterium than larvae feeding on deer, birds, or other mammals. When those larvae molt into nymphs the following year, the infected nymphs become the primary threat to humans, delivering the bite that transmits Lyme disease in the vast majority of cases.

Interrupting the cycle at the mouse-tick interface has therefore long been an attractive target for researchers. Earlier laboratory and simulated field studies had already demonstrated that a bait containing just 0.005 percent fipronil could systemically control Ixodes scapularis ticks parasitizing treated white-footed mice. Fipronil, the same active ingredient found in some companion-animal flea and tick products, works systemically: after a mouse ingests the bait, the compound and its metabolites circulate in the animal’s blood, and ticks that attach and begin feeding are killed before they can complete their blood meal. The question the Connecticut study set out to answer was whether that laboratory promise would survive contact with real backyards, real weather, and real wildlife.

Between 2022 and 2024, the research team deployed reusable rodent bait stations on residential properties during the period when blacklegged ticks are active in their nymphal and larval stages, roughly May through August. The stations dispensed the fipronil-treated bait to free-ranging mice, and the team monitored consumption, replenishing bait as needed to keep the system running through each season. On average, each property received 4.9 kilograms of bait per year, which translates to approximately 247 milligrams of fipronil—a remarkably small total quantity of active ingredient distributed across an entire property over an entire season.

To confirm that the mice were actually being exposed to the compound, the researchers captured white-footed mice during the larval season each year on both treated and untreated control properties and analyzed their blood plasma. The results were striking: fipronil sulfone, a metabolite that serves as a marker of exposure, was detectable in 100 percent of plasma samples analyzed in both 2022 and 2023, and in 83.3 percent of samples in 2024. In other words, the bait stations were doing their job, delivering the active ingredient to the target animals with high consistency even under fully natural field conditions.

The effect on the ticks themselves was even more impressive. On treated properties, the number of larvae parasitizing captured mice fell by up to 84.2 percent compared with control properties, and the number of larvae that successfully engorged—those that managed to complete a blood meal, which is the critical step for both tick survival and pathogen acquisition—dropped by up to 92.5 percent. A larval tick that fails to engorge on a mouse not only fails to acquire Borrelia from that mouse; it also faces greatly reduced odds of surviving to molt into the next life stage. The bait, in effect, turned the most important host in the Lyme disease system into a lethal trap for its parasites.

The benefits extended to the pathogen as well. Molecular assays used to detect Borrelia burgdorferi infection in the captured mice showed that infection prevalence in white-footed mice on treated properties was significantly reduced by up to 34.1 percent relative to controls. That reduction matters because fewer infected mice means fewer larval ticks acquiring the spirochete, which in principle should mean fewer infected nymphs questing for human blood the following spring. The study thus demonstrated a measurable dent in the reservoir competence of the local mouse population, achieved not by reducing mouse numbers but by breaking the tick-mouse transmission loop.

The picture was more nuanced, however, when the researchers turned to the stage of the tick life cycle that matters most for human health. Drag sampling and flagging during the nymphal seasons were used to estimate the abundance of host-seeking nymphs on the properties, and molecular testing assessed how many of those nymphs carried Borrelia. While both nymph density and nymphal infection showed reductions on treated properties, neither difference reached statistical significance compared with the control sites. The authors suggest that the bait application rate during the larval season may need to be increased to push these downstream effects over the threshold of detectability—a reminder that intervening at one link of a complex transmission chain does not automatically translate into reduced risk at every other link.

That caveat aside, the study represents one of the most thorough field evaluations to date of a systemic acaricide bait aimed at the wildlife reservoir of Lyme disease. Its design—multi-year, property-level, with matched controls, bait-consumption monitoring, pharmacokinetic confirmation, and molecular pathogen testing on both rodents and questing ticks—addresses many of the weaknesses that have plagued earlier tick-control trials. The extremely low dose of active ingredient involved also raises the prospect of an environmentally targeted intervention: rather than broadcasting insecticides across vegetation, the treatment is delivered only to the small mammals that seek out the bait stations, and only in quantities measured in hundreds of milligrams per property per year.

The researchers, based at Genesis Laboratories in Colorado and the Connecticut Agricultural Experiment Station, were supported by a contract with the United States Centers for Disease Control and Prevention, and the work benefited from molecular detection assistance from CDC scientists. They emphasize that additional field studies are needed to confirm the findings and to explore what large-scale treatment across neighborhoods or landscapes might achieve, since tick populations on untreated properties can continually seed treated areas. Still, the core result stands: a bait box, a few hundred milligrams of fipronil, and the natural foraging behavior of white-footed mice were enough to strip the vast majority of larval ticks from the animals that sustain Lyme disease in the northeastern United States. As integrated tick management strategies evolve, the humble mouse bait station may prove to be one of the most quietly powerful tools in the fight against America’s most common vector-borne disease.

Subject of Research: Field efficacy of low-dose fipronil bait for controlling blacklegged ticks on white-footed mice and reducing Lyme disease transmission

Article Title: Efficacy of a low-dose fipronil bait in controlling blacklegged tick (Ixodes scapularis) larvae parasitizing white-footed mice (Peromyscus leucopus) under field conditions in the northeastern United States

Article References: Poché, D. M., Williams, S. C., Linske, M. A., & Poché, R. M. (2026). Efficacy of a low-dose fipronil bait in controlling blacklegged tick (Ixodes scapularis) larvae parasitizing white-footed mice (Peromyscus leucopus) under field conditions in the northeastern United States. Parasites & Vectors, 19(1), Article 423. https://doi.org/10.1186/s13071-026-07676-8

Image Credits: AI Generated

DOI: 10.1186/s13071-026-07676-8

Keywords: Lyme disease, Ixodes scapularis, Peromyscus leucopus, fipronil, tick control, Borrelia burgdorferi, vector-borne disease, systemic acaricide, bait stations, integrated tick management, Connecticut, public health