Seroprevalence of Borrelia burgdorferi, B. miyamotoi, and Powassan Virus in Residents Bitten by Ixodes Ticks, Maine, USA.

We conducted a serosurvey of 230 persons in Maine, USA, who had been bitten by Ixodes scapularis or I. cookei ticks. We documented seropositivity for Borrelia burgdorferi (13.9%) and B. miyamotoi (2.6%), as well as a single equivocal result (0.4%) for Powassan encephalitis virus.

Human babesiosis, Maine, USA, 1995-2011.

We observed an increase in the ratio of pathogenic Babesia microti to B. odocoilei in adult Ixodes scapularis ticks in Maine. Risk for babesiosis was associated with adult tick abundance, Borrelia burgdorferi infection prevalence, and Lyme disease incidence. Our findings may help track risk and increase the focus on blood supply screening.

Effect of a botanical acaricide on Ixodes scapularis (Acari: Ixodidae) and nontarget arthropods.

We tested the effectiveness of the rosemary oil-based insecticide, Eco-Exempt IC2, to control all stages of Ixodes scapularis (Say) in southern Maine. We selected plots in oak-pine forest where I. scapularis is endemic and recorded the abundance of ticks and nontarget arthropods before and after applications of IC2, bifenthrin (a synthetic pyrethroid), and water (reference treatment). Licensed applicators applied high-pressure spray treatments during the summer nymphal and fall adult seasonal peaks. Both acaricides sprayed during the summer nymphal season reduced nymphal I. scapularis/hour to zero. IC2 was as effective as bifenthrin in controlling nymphs through the rest of the nymphal season and also controlled adult ticks 9 mo postspray compared with 16 mo for bifenthrin, and both acaricides reduced larvae through 14 mo postspray. Both acaricides sprayed during the fall adult season reduced adult I. scapularis/hour to zero; IC2 controlled adult ticks 6 mo postspray compared with 1 yr for bifenthrin. Both fall-applied acaricides controlled nymphs 9 mo postspray and reduced larvae up to 10 mo postspray. Impacts on some nontarget arthropods was assessed. Colleoptera, Hymenoptera, and Collembola declined 1 wk postspray in acaricide-treated plots, and in IC2 plots all numbers rebounded by 20 d postspray. For bees and other flower-visiting insects there were no detectable reductions in nests produced, number emerged from nests, or number of foraging visits to flowering plants in IC2 or bifenthrin plots. IC2 was phytotoxic to the leafy portions of select understory plants that appeared to recover by the next growing season.

Multitarget test for emerging Lyme disease and anaplasmosis in a serosurvey of dogs, Maine, USA.

To determine if the range of deer ticks in Maine had expanded, we conducted a multitarget serosurvey of domestic dogs (Canis lupus familiaris) in 2007. An extension of exposure to Borrelia burgdorferi to the northern border and local transmission of Anaplasma phagocytophilum throughout southern areas was found.

Trial of a minimal-risk botanical compound to control the vector tick of Lyme disease.

We compared the application of IC2, a minimal-risk (25B) botanical compound containing 10% rosemary oil, with bifenthrin, a commonly used synthetic compound, and with water for the control of Ixodes scapularis Say (= Ixodes dammini Spielman, Clifford, Piesman & Corwin), on tick-infested grids in Maine, in an area where Lyme disease is established and other tick-borne diseases are emerging. High-pressure sprays of IC2, bifenthrin, and water were applied during the peak nymphal (July) and adult (October) seasons of the vector tick. No ticks could be dragged on the IC2 grids within 2 wk of the July spray, and few adult ticks were found in October or the following April. Similarly, no adult ticks could be dragged 1.5 wk after the October IC2 spray, and few the following April. No ticks were found on the bifenthrin grids after either spray through the following April, whereas substantial numbers of ticks remained throughout on the grids sprayed with water. Thus, IC2 appears to be an effective, minimum-risk acaricide to control the vector tick of Lyme disease.

Decoupling of Blacklegged Tick Abundance and Lyme Disease Incidence in Southern Maine, USA.

Lyme disease is caused by the bacterial spirochete Borrelia burgdorferi Johnson, Schmid, Hyde, Steigerwalt, and Brenner (Spirocheatales: Spirochaetaceae) which is transmitted through the bite of an infected blacklegged tick Ixodes scapularis Say (Ixodida: Ixodidae). Maine, USA, is a high Lyme disease incidence state, with rising incidence of Lyme disease and other tick-borne illnesses associated with increasing I. scapularis abundance and northward range expansion. Members of the public submitted ticks to a tick identification program (1990-2013). From these passive surveillance data, we characterized temporal trends in I. scapularis submission rate (an index of abundance), comparing Maine's northern tier (seven counties) versus southern tier (nine counties). In the northern tier, the I. scapularis submission rate increased throughout the duration of the time series, suggesting I. scapularis was emergent but not established. By contrast, in the southern tier, submission rate increased initially but leveled off after 10-14 yr, suggesting I. scapularis was established by the mid-2000s. Active (field) surveillance data from a site in the southern tier-bird tick burdens and questing adult tick collections-corroborated this leveling pattern. Lyme disease incidence and I. scapularis submission rate were temporally correlated in the northern but not southern tier. This suggested a decoupling of reported disease incidence and entomological risk.

Passive surveillance in Maine, an area emergent for tick-borne diseases.

In 1989, a free-of-charge, statewide tick identification program was initiated in Maine, 1 yr after the first Ixodes scapularis Say (=I. dammini Spielman, Clifford, Piesman & Corwin) ticks were reported in the state. This article summarizes data from 18 continuous years of tick submissions during which >24,000 ticks of 14 species were identified. Data provided include tick stage, degree of engorgement, seasonal abundance, geographical location, host, and age of the person from whom the tick was removed. Maps depict the distributions of the three major species submitted. I. scapularis emerged first along the coast, and then it advanced inland up major river valleys, Dermacentor variabilis Say slowly expanded centrifugally from where it was initially reported in southwestern Maine, and the distribution of long-established Ixodes cookei Packard remained unchanged. Submissions of nymphal I. scapularis closely correlated with reported Lyme diseases cases at the county level. Annual fluctuations of nymphal submissions in Maine correlated with those of Lyme disease cases for New England, supporting the possibility of a regional influence on tick abundance. More ticks were removed from people < or =14 and > or =30 yr of age, and their degree of engorgement was greatest in people < or =20 yr of age and progressively increased in people > or =30 yr of age. This study demonstrates the usefulness and potential of tick identification programs.

First U.S. record of the hard tick Ixodes (Pholeoixodes) gregsoni Lindquist, Wu, and Redner.

Ixodes (Pholeoixodes) gregsoni Lindquist, Wu, and Redner, a species of hard tick described in 1999 in Canada, was recovered from a harvested fisher (Martes pennanti Erxleben) and a domestic cat (Felis silvestris catus Ragni and Randi) in Vermont in 2001 and from harvested mink (Mustela vison Schreber) in Maine in 2003. These samples are the first records of this species within the United States. Although knowledge of this tick's natural history and distribution are still preliminary, these records indicate a possible greater distribution for I. gregsoni than initially perceived. Although its status as a disease vector is presently unknown, natural resource professionals should be aware of the possibility of this tick's occurrence in the northeastern United States.

Seasonal Patterns in Eastern Equine Encephalitis Virus Antibody in Songbirds in Southern Maine.

The intent of this study was to assess passerine eastern equine encephalitis virus (EEEv) seroprevalence during the breeding season in southern Maine by testing songbird species identified in the literature as amplifying hosts of this virus. In 2013 and 2014, we collected serum samples from songbirds at a mainland site and an offshore island migratory stopover site, and screened samples for EEEv antibodies using plaque reduction neutralization tests. We compared seasonal changes in EEEv antibody seroprevalence in young (hatched in year of capture) and adult birds at the mainland site, and also compared early season seroprevalence in mainland versus offshore adult birds. EEEv seroprevalence did not differ significantly between years at either site. During the early season (May), EEEv antibody seroprevalence was substantially lower (9.6%) in the island migrant adults than in mainland adults (42.9%), 2013-2014. On the mainland, EEEv antibody seroprevalence in young birds increased from 12.9% in midseason (June-August) to 45.6% in late season (September/October), 2013-2014. Seroprevalence in adult birds did not differ between seasons (48.8% vs. 53.3%). EEEv activity in Maine has increased in the past decade as measured by increased virus detection in mosquitoes and veterinary cases. High EEEv seroprevalence in young birds-as compared to that of young birds in other studies-corresponded with two consecutive active EEEv years in Maine. We suggest that young, locally hatched songbirds be sampled as a part of long-term EEEv surveillance, and provide a list of suggested species to sample, including EEEv "superspreaders."

Deer browse resistant exotic-invasive understory: an indicator of elevated human risk of exposure to Ixodes scapularis (Acari: Ixodidae) in southern coastal Maine woodlands.

We evaluated the relationships between forest understory structure and the abundance of questing adult and nymphal blacklegged ticks, Ixodes scapularis Say (Acari: Ixodidae), in three Maine towns endemic for Lyme disease, 2001-2003. In fragmented New England woodlands, over-abundant white-tailed deer, Odocoileus virginianus Zimmerman, overbrowse palatable species, allowing browse-resistant exotic-invasive species to replace native forest understory structures. We predicted there would be more ticks in plots dominated by exotic-invasive shrubs (such as Japanese barberry, Berberis thunbergii DC) than in plots dominated by native shrubs, ferns, or open understory. We assessed canopy composition and closure, tree basal area, litter composition, percentage of coverage and stem density of understory species, litter depth, soil moisture, and abundance of small mammals and white-tailed deer pellet groups. We used generalized linear mixed model analysis of covariance to determine the effect of understory structure on tick counts, controlling for continuous habitat and host covariates and adjusting for random spatial effects. There were twice as many adults and nearly twice as many nymphs in plots dominated by exotic-invasives than in plots dominated by native shrubs. Both adult and nymphal counts were lowest in open understory with coniferous litter. Adults were positively associated with increasing litter depth, medium soil moisture, and increasing abundance of white-footed deer mice, Peromyscus leucopus Rafinesque, and deer pellet group counts. Nymphs were positively associated with increasing litter depth, moderately wet soil, and mice. We concluded that deer browse-resistant exotic-invasive understory vegetation presented an elevated risk of human exposure to the vector tick of Lyme disease.

Abundance of Ixodes scapularis (Acari: Ixodidae) after the complete removal of deer from an isolated offshore island, endemic for Lyme Disease.

Monhegan is an isolated 237-ha island lying 16 km off the coast of Maine. Introduced to the island in 1955, white-tailed deer, Odocoileus virginianus Zimmerman, reached a density of approximately 37/km2 by the mid-1990s. Black-legged ticks, Ixodes scapularis Say, first noticed in the late 1980s, flourished thereafter. Norway rats (Rattus norvegicus Berkenhout) on Monhegan are highly infected with Borrelia burgdorferi Johnson, Schmidt, Hyde, Steigerwalt, and Brenner, the agent of Lyme disease. By 1996, 13% of year-round residents had contracted the disease. The community's subsequent decision to eliminate deer from the island provided a unique opportunity to monitor the abundance of vector ticks in response to the complete and permanent removal of the primary hosts of their reproductive stage. With the exception of humans and their dogs and cats, there are no other potential hosts for adult I. scapularis on Monhegan. From November 1996 to March 1999, all deer were removed from the island. Previous annual fall flagging of vegetation from 1990 to 1998 produced 6-17 adult ticks/h, of which 24-41% were infected with the Lyme disease spirochete. During this same period, up to 18 larvae and 4 nymphs were removed per Norway rat live-trapped on the island each July. With the absence of deer in the fall of 1999, both the density of host-seeking adult ticks and infection prevalence rose substantially to 28/h and 75.0%, respectively. By the summer of 2003, however, no sub-adult ticks were found on rats, and that fall, only 0.67 adult ticks/h were flagged. Of the 68 adults collected from 2002 to 2003, 20 (29.4%) were infected. Over this same period, adult tick abundance on a deer-populated, reference island continued to gradually increase.

Deer density and the abundance of Ixodes scapularis (Acari: Ixodidae).

The abundance of Ixodes scapularis Say (Ixodes dammini Spielman, Clifford, Piesman & Corwin), the vector tick of the Lyme disease spirochete and other human pathogens, is related to the presence of its primary reproductive stage host, white-tailed deer (Odocoileus virginianus Zimmerman). However, this relationship has not been quantified in terms that would guide wildlife management in areas in which the public is, or is likely to become, exposed to infected ticks. In this study, deer density and tick abundance were measured in an emergent area for Lyme disease at three spatial scales using estimation methods appropriate for each. Simple linear regression was used to relate (1) the number of ticks found on deer at tagging stations in southern Maine to harvest-derived estimates of the density of deer within the towns in which they were killed, (2) tick densities estimated from fall flagging counts to deer densities estimated from pellet group counts made within multiple transects distributed through 5.2-km2 study sites, and (3) tick counts to pellet group counts within the individual transects. At the broadest scale, ticks on deer decreased with elevation and distance from the coast and increased with deer density, although deer and tick presence were only weakly related. Among the 5.2-km2 study sites and within individual transects, tick abundance related more strongly to deer pellet group counts. Few ticks were collected at deer densities <7/km2.

Thermal accumulation and the early development of Ixodes scapularis.

We examined the relationship between the accumulation of thermal energy and the onset of oviposition and eclosion of the northern deer tick, Ixodes scapularis, and explored the usefulness of comparing degree days (DD) required for larval emergence with area-wide National Weather Service (NWS) data to construct maps indicating where the establishment of this vector tick would be climatologically constrained. Initially, the validity of basal temperatures for egg and larval development was confirmed by prolonged incubations of gravid females and eggs at 6 degrees C and 10 degrees C respectively. Next, the number of DD accumulated in situ from the placement of gravid females to oviposition, and from oviposition to larval emergence, were measured using temperature data loggers placed next to fall- and spring-fed ticks held within individual vials under leaf litter in multiple enclosures located in diverse biophysical regions of Maine. Finally, when it was found that total DD to larval emergence, as measured in ambient air above the enclosures, compared favorably with DD accumulated simultaneously at nearby NWS stations, maps were constructed, based on archived NWS data, to demonstrate where temperatures were sufficient to allow the hatching of larvae both within one season and over the last three decades as I. scapularis has advanced into northern New England.

Parasitism of mustelids by ixodid ticks (Acari: Ixodidae), Maine and New Hampshire, U.S.A.

Ticks collected from mustelids from four counties in Maine and one in New Hampshire were identified after harvest. Of the 18 fishers Martes pennanti Erxleben, two mink Neovison vison Schreber, and one long-tailed weasel Mustela frenata Lichtenstein, 589 ticks were collected and identified. They were identified as, in order of abundance, Ixodes gregsoni Lindquist, Wu, and Redner (158 larvae, 189 nymphs, four adults), Ixodes cookei Packard (99 larvae, 77 nymphs, six adults), Ixodes scapularis Say (53 adults), Dermacentor variabilis Say (two nymphs), and Ixodes angustus Neumann (one nymph). Seasonally, all but the D. variabilis were collected in winter. This study reports the first record of adult I. scapularis from a M. pennanti in the northeastern United States.

Genotypic diversity of an emergent population of Borrelia burgdorferi at a coastal Maine island recently colonized by Ixodes scapularis.

The recent range expansion of Ixodes scapularis has been accompanied by the emergence of Borrelia burgdorferi. The development of genetic diversity in B. burgdorferi at these sites of emergence and its relationship to range expansion is poorly understood. We followed colonization of I. scapularis on a coastal Maine island over a 17-year period. B. burgdorferi's emergence was documented, as was expansion of ospC strain diversity. Ticks collected from rodents and vegetation were examined for the presence of B. burgdorferi. Sequencing and reverse line blot were used to detect B. burgdorferi ospC major groups (oMG). No I. scapularis were found until year four of the study, after which time they increased in abundance. No B. burgdorferi was detected by darkfield microscopy in I. scapularis until 10 years into the study, when 4% of adult ticks were infected. Seven years later, 43% of adult ticks were infected. In 2003, one oMG accounted for 91% of B. burgdorferi strains. This "founder" strain persisted in 2005, but by 2007 was a minority of the 7 oMGs present. Given the island's isolation, gene flow by avian introduction of multiple strains is suggested in the development of B. burgdorferi oMG diversity.

Density of Ixodes scapularis ticks on Monhegan Island after complete deer removal: a question of avian importation?

Questing adult blacklegged tick (Ixodes scapularis Say) abundance declined markedly three years after the 1999 removal of white-tailed deer (Odocoileus virginianus Zimmermann) from Monhegan Island, ME. Since 2000, subadult ticks have not been found on Norway rats (Rattus norvegicus Berkenhout); questing nymphs have not been found since 2002. This suggested I. scapularis was reintroduced annually via bird importation of subadult ticks, but unable to complete its two-year life cycle on the island due to lack of deer. To investigate this, we used uncertainty analysis to estimate 1) questing adult ticks/ha that would result from avian importation of nymphs, and 2) questing adult ticks/ha on Monhegan Island, using bird capture and tick burden data from Appledore Island, ME, flagged tick data from Monhegan Island, and ten uncertain parameters. During the deer-fed period (1990-2001), estimated tick density on Monhegan Island was 18 times greater than that of imported ticks. During the post-deer-fed period (2002-2008), Monhegan Island tick density was equivalent to imported tick density. This supported the premise that all I. scapularis ticks on Monhegan Island have been bird-derived since 2002.

Increased recognition of Powassan encephalitis in the United States, 1999-2005.

Powassan virus (POWV) disease is a rare human disease caused by a tick-borne encephalitis group flavivirus maintained in a transmission cycle between Ixodes cookei and other ixodid ticks and small and medium-sized mammals. During 1958-1998, only 27 POWV disease cases (mostly Powassan encephalitis) were reported from eastern Canada and the northeastern United States (average, 0.7 cases per year). During 1999-2005, nine cases (described herein) of serologically confirmed POWV disease were reported in the United States (average, 1.3 cases per year): four from Maine, two from New York, and one each from Michigan, Vermont, and Wisconsin. The Michigan and Wisconsin cases are the first ever reported from the north-central United States. Of these nine patients, 5 (56%) were men, the median age was 69 years (range: 25-91 years), and 6 (67%) had onset during May-July. All but one patient developed encephalitis with acute onset of profound muscle weakness, confusion, and other severe neurologic signs. In one case, no neurologic symptoms were present but the presence of pleocytosis, an elevated cerebrospinal fluid (CSF) protein concentration, and POWV-specific immunoglobulin M in CSF suggested neuroinvasion. All patients recovered from their acute disease, but most had long-term neurologic sequelae. Periresidential ecologic investigations were performed in three cases, including tests of local mammals and ticks for evidence of POWV infection. Woodchucks (Marmota monax), striped skunks (Mephitis mephitis), and a raccoon (Procyon lotor) collected at two of the Maine case-patients' residences had neutralizing antibody titers to POWV. I. cookei were found on woodchucks and skunks and questing in grassy areas of one of these residences; all were negative for POWV. Although POWV disease is rare, it is probably under-recognized, and it causes significant morbidity, and thus is an additional tick-borne emerging infectious disease entity. Because no vaccine or specific therapy is available, the basis of prevention is personal protection from ticks (or "tick hygiene") and reduced exposure to peridomestic wild mammals.

Borrelia garinii in seabird ticks (Ixodes uriae), Atlantic Coast, North America.

Borrelia garinii is the most neurotropic of the genospecies of B. burgdorferi sensu lato that cause Lyme disease in Europe, where it is transmitted to avian and mammalian reservoir hosts and to humans by Ixodes ricinus. B. garinii is also maintained in an enzootic cycle in seabirds by I. uriae, a tick found at high latitudes in both the Northern and Southern Hemispheres. To determine whether B. garinii is present in seabird ticks on the Atlantic Coast of North America, we examined 261 I. uriae ticks by polyclonal antiborrelial fluorescent antibody. Ten of 61 ticks from Gull Island, Newfoundland, were positive for borreliae by this screen. Amplicons of DNA obtained by PCR that targeted the B. garinii rrs-rrla intergenic spacer were sequenced and matched to GenBank sequences for B. garinii. The potential for introduction of this agent into the North American Lyme disease enzootic is unknown.

Antibody testing and Lyme disease risk.

Lyme disease test results for >9,000 dogs were collected from participating veterinary clinics. Testing was conducted by using the IDEXX 3Dx kit, used widely by Maine veterinarians to screen clinically normal dogs during heartworm season. This study demonstrates how this test can be a valuable public health disease surveillance tool.