[Show abstract][Hide abstract] ABSTRACT: Pathogen prevalence within blacklegged ticks (Ixodes scapularis Say, 1821) tends to vary across sites and geographic regions, but the underlying causes of this variation are not well understood. Efforts to understand the ecology of Lyme disease have led to the proposition that sites with higher host diversity will result in lower disease risk due to an increase in the abundance of inefficient reservoir species relative to the abundance of species that are highly competent reservoirs. Although the Lyme disease transmission cycle is often cited as a model for this " dilution effect hypothesis " , little empirical evidence exists to support that claim. Here we tested the dilution effect hypothesis for two pathogens transmitted by the blacklegged tick along an urban-to-rural gradient in the northeastern United States using landscape fragmentation as a proxy for host biodiversity. Percent impervious surface and habitat fragment size around each site were determined to assess the effect of landscape fragmentation on nymphal blacklegged tick infection with Borrelia burgdorferi and Ana-plasma phagocytophilum. Our results do not support the dilution effect hypothesis for either pathogen and are in agreement with the few studies to date that have tested this idea using either a landscape proxy or direct measures of host biodiversity.
PLoS ONE 10/2015; 10(10). DOI:10.1371/journal.pone.0139473 · 3.23 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Deer tick virus, DTV, is a genetically and ecologically distinct lineage of Powassan virus (POWV) also known as lineage II POWV. Human incidence of POW encephalitis has increased in the last 15 years potentially due to the emergence of DTV, particularly in the Hudson Valley of New York State. We initiated an extensive sampling campaign to determine whether POWV was extant throughout the Hudson Valley in tick vectors and/or vertebrate hosts.
More than 13,000 ticks were collected from hosts or vegetation and tested for the presence of DTV using molecular and virus isolation techniques. Vertebrate hosts of Ixodes scapularis (black-legged tick) were trapped (mammals) or netted (birds) and blood samples analyzed for the presence of neutralizing antibodies to POWV. Maximum likelihood estimates (MLE) were calculated to determine infection rates in ticks at each study site.
Evidence of DTV was identified each year from 2007 to 2012, in nymphal and adult I. scapularis collected from the Hudson Valley. 58 tick pools were positive for virus and/or RNA. Infection rates were higher in adult ticks collected from areas east of the Hudson River. MLE limits ranged from 0.2-6.0 infected adults per 100 at sites where DTV was detected. Virginia opossums, striped skunks and raccoons were the source of infected nymphal ticks collected as replete larvae. Serologic evidence of POWV infection was detected in woodchucks (4/6), an opossum (1/6), and birds (4/727). Lineage I, prototype POWV, was not detected.
These data demonstrate widespread enzootic transmission of DTV throughout the Hudson Valley, in particular areas east of the river. High infection rates were detected in counties where recent POW encephalitis cases have been identified, supporting the hypothesis that lineage II POWV, DTV, is responsible for these human infections.
[Show abstract][Hide abstract] ABSTRACT: Wetlands provide a variety of services to society; however, their use as breeding habitat by mosquitoes has caused concern
that they pose a risk to human health. As mosquito-borne diseases are undergoing a global resurgence, there is a need to better
understand the factors that influence mosquito production in wetlands. Seasonal pools offer a model system in which to study
mosquito production as they provide breeding habitat for many mosquito species. In the northeastern US, larval spotted salamanders
(Ambystoma maculatum) and wood frog tadpoles (Lithobates sylvaticus) are common in pools and may affect mosquito growth and survival through predation or competition. To determine if these
species interact, we conducted surveys of pools and found that larval mosquitoes were less abundant in pools with higher densities
of larval salamanders. Experiments on mosquito oviposition and survival found that mosquitoes avoided ovipositing in habitats
containing larval salamanders and tadpoles and had low survival in the presence of salamanders. These data indicate that predation
by larval salamanders may influence the breeding distribution of mosquitoes by imposing selective pressure on ovipositing
adults. Therefore, developing measures to protect amphibians in seasonal pools may contribute to controlling mosquito production
in wetlands, potentially minimizing disease risk to humans.
KeywordsPredation–Temporary pools–Vernal pools–Wetland protection
[Show abstract][Hide abstract] ABSTRACT: Ixodes scapularis Say, the blacklegged tick, vectors Borrelia burgdorferi [Johnson et al. 1984], the bacterium that causes Lyme disease, the most important vector-borne disease in the United States. Efforts to reduce I. scapularis populations are shifting toward the development of biological control methods. Currently, only a few entomopathogenic fungal species are considered virulent to ticks. We hypothesized that these species may not represent the most abundant local taxa that would be pathogenic to ticks in situ. To identify potential entomopathogenic fungi at a study site in Westchester County, New York, we sampled soils and ticks, extracted and amplified the internal transcribed spacer region of nuclear ribosomal DNA (nrDNA), and compared sequences with those in GenBank. Over three sampling periods from June 2007 to May 2008, 70 fungal taxa were isolated and identified from soils (48 taxa) and ticks (27 taxa; 5 taxa were found both in soil and on ticks) collected in this study, encompassing species in 25 different genera. In laboratory bioassays, 15 fungal taxa were found to be significantly virulent, although none of these were previously considered common pathogens of I. scapularis . Two species, Hypocrea lixii Patouillard 1891 and Penicillium soppii K. M. Zalessky 1927, were tested in field trials by spraying suspensions on forested plots. Mean tick mortality was 71% after treatment with H. lixii , 58% after treatment with P. soppii , and 32% in the control plots. The complete diversity of entomopathogenic fungal species at this site is yet to be defined, but, in general, such fungi appear to be more common in forest habitats where I. scapularis resides than previously thought. Examination of intact fungal communities can provide information that serves as the foundation for site-specific biocontrol programs.
Journal of Medical Entomology 03/2011; 48(2):337-44. DOI:10.1603/ME09116 · 1.95 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: The efficacy of topically treating white-tailed deer with an acaricide was evaluated in a Lyme disease-endemic community of southern New York State. Twenty-four 4-Poster feeders were placed in a 5.2 km(2) treatment area in Bedford, NY, while a site in Lewisboro, NY, 4.8 km distant, served as control. Treatment periods ran from 15 September to 15 December each fall from 1997 to 2001, and from 15 March to 15 May each spring from 1998 to 2002. Corn consumption averaged 15,779 kg in fall sessions and 9054 kg in spring sessions, and a mean of 89.6% of deer in the study area showed evidence of using the feeders. Deer densities, estimated by aerial snow counts, averaged 22 and 28 deer per km(2) in Bedford and Lewisboro, respectively, over a 3-year period. Significant reductions in tick numbers on deer captured in the treatment area were noted in fall 1999 compared to deer captured at the control site. Drag sampling for nymphal host-seeking ticks indicated 63.6% control in 2001, which dropped to 54.8% the following year, but reached 80% in 2003. Higher-than-normal acorn production in 2001 that likely caused a drop in deer visitation to the feeders may have reduced efficacy against larval ticks in 2002. The 4-Poster effectively reduced the density of Ixodes scapularis, though the level of control is dependent on environmental factors that affect feeding behavior of white-tailed deer.
[Show abstract][Hide abstract] ABSTRACT: As part of the Northeast Area-wide Tick Control Project (NEATCP), meta-analyses were performed using pooled data on the extent of tick-vector control achieved through seven concurrent studies, conducted within five states, using U.S. Department of Agriculture "4-Poster" devices to deliver targeted-acaricide to white-tailed deer. Although reductions in the abundance of all life-stages of Ixodes scapularis were the measured outcomes, this study focused on metrics associated with I. scapularis nymphal tick densities as this measure has consistently proven to directly correlate with human risk of acquiring Lyme disease. Since independent tick sampling schemes were undertaken at each of the five environmentally distinct study locations, a meta-analytic approach permitted estimation of a single true control-effect size for each treatment year of the NEATCP. The control-effect is expressed as the annual percent I. scapularis nymphal control most consistent with meta-analysis data for each treatment year. Our meta-analyses indicate that by the sixth treatment year, the NEATCP effectively reduced the relative density of I. scapularis nymphs by 71% on the 5.14 km(2) treatment sites, corresponding to a 71% lower relative entomologic risk index for acquiring Lyme disease.
[Show abstract][Hide abstract] ABSTRACT: From 1997 to 2002, the U.S. Department of Agriculture's Northeast Area-wide Tick Control Project used acaricide-treated 4-Poster Deer Treatment Bait Stations in five eastern states to control ticks feeding on white-tailed deer. The objectives of this host-targeted technology were to reduce free-living blacklegged (Ixodes scapularis Say) and lone star (Amblyomma americanum [L.]) tick populations and thereby to reduce the risk of tick-borne disease. During 2002 to 2004, treatments were suspended, and tick population recovery rates were assayed. Subsequently, the major factors that influenced variations in efficacy were extrapolated to better understand and improve this technology. Treatments resulted in significant reductions in free-living populations of nymphal blacklegged ticks at six of the seven sites, and lone star ticks were significantly reduced at all three sites where they were present. During the study, maximal significant (p < or = 0.05) efficacies against nymphal blacklegged and lone star ticks at individual sites ranged from 60.0 to 81.7 and 90.9 to 99.5%, respectively. The major environmental factor that reduced efficacy was the occurrence of heavy acorn masts, which provided an alternative food resource for deer. Although the 4-Poster technology requires 1 or more years to show efficacy, this host-targeted intervention was demonstrated to be an efficacious, economical, safe, and environment-friendly alternative to area-wide spraying of acaricide to control free-living populations of these tick species.
[Show abstract][Hide abstract] ABSTRACT: Entomopathogenic fungi are commonly found in forested soils that provide tick habitat, and many species are pathogenic to Ixodes scapularis Say, the blacklegged tick. As a first step to developing effective biocontrol strategies, the objective of this study was to determine the best methods to isolate entomopathogenic fungal species from field-collected samples of soils and ticks from an Eastern deciduous forest where I. scapularis is common. Several methods were assessed: (1) soils, leaf litter, and ticks were plated on two types of media; (2) soils were assayed for entomopathogenic fungi using the Galleria bait method; (3) DNA from internal transcribed spacer (ITS) regions of the nuclear ribosomal repeat was extracted from pure cultures obtained from soils, Galleria, and ticks and was amplified and sequenced; and (4) DNA was extracted directly from ticks, amplified, and sequenced. We conclude that (1) ticks encounter potentially entomopathogenic fungi more often in soil than in leaf litter, (2) many species of potentially entomopathogenic fungi found in the soil can readily be cultured, (3) the Galleria bait method is a sufficiently efficient method for isolation of these fungi from soils, and (4) although DNA extraction from ticks was not possible in this study because of small sample size, DNA extraction from fungi isolated from soils and from ticks was successful and provided clean sequences in 100 and 73% of samples, respectively. A combination of the above methods is clearly necessary for optimal characterization of entomopathogenic fungi associated with ticks in the environment.
Journal of Medical Entomology 06/2009; 46(3):557-65. DOI:10.1603/033.046.0321 · 1.95 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: A polymorphic multigene family (p44) of Anaplasma phagocytophilum encodes the immunodominant 44-kDa major outer membrane proteins. With p44-specific PCR and gene-specific probes, p44-1 was found in all human isolates from New York State but not in isolates from Minnesota, whereas p44-18 and two other p44 species were found in isolates from both regions. We therefore sequenced the genomic locus corresponding to the p44-1/p44-18 tandem locus of A. phagocytophilum HZ in 14 other geographically divergent strains from various hosts. The locus was found in all 14 strains, and p44-18 was conserved among all 13 United States isolates studied. In all nine northeastern strains, p44-1 was conserved. However, in three of the Minnesota strains and in one California strain, p44-1 was replaced at this genomic locus by the novel gene p44-61 (p44-61/18), whose hypervariable region (hv) was a chimera of p44-20hv and p44-23hv. The conserved base sequence within the hv region linked the two segments. In contrast, in the Old Sourhope strain isolated from sheep in the United Kingdom, only a single and distinct p44, p44-OS, was found in this locus. This suggests different rates of evolution of p44-1 and p44-18 at this locus and conservation of the locus within strains isolated from the same geographic region. Locus-specific reverse transcription-PCR revealed expression of p44-1 by New York and p44-61 by Minnesota strains at this locus. These p44 loci provide insight into the molecular evolution and functional divergence of p44 paralogs and may serve as markers for typing strains from different geographic regions.
Infection and Immunity 11/2004; 72(10):5574-81. DOI:10.1128/IAI.72.10.5574-5581.2004 · 3.73 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: The 44-kDa immunodominant outer membrane proteins (P44 proteins) of Anaplasma phagocytophilum are encoded by the p44 polymorphic multigene family. The present study examined p44 expression and analyzed the cDNA sequences of various p44 transcripts from the spleens and blood of mice infected by the bites of ticks infected with the A. phagocytophilum NTN-1 strain or of naturally infected nymphal ticks and in the salivary glands and midgut tissues of these ticks. A total of 300 p44 cDNAs were subjected to sequence analysis. Of these, 40 distinct p44 species were found, and all of these had orthologs in the A. phagocytophilum HZ strain genome that shared 95 to 100% base sequence identity. The number of unique p44 species expressed in mouse blood was greater than that for mouse spleens. Higher numbers of different p44 transcripts were also expressed in the salivary glands of ticks than in the midgut tissues. Variations in the sequences of the same p44 cDNA species within a single A. phagocytophilum strain and among different strains were concentrated in the conserved regions flanking the central hypervariable region of p44 genes. No mosaic sequences derived from two or more p44 species were found within the p44 hypervariable region. The conservation of the hypervariable region of each p44 cDNA species of A. phagocytophilum in naturally infected ticks and in different geographic isolates suggests that each A. phagocytophilum genome carries a set of p44 paralogs to be expressed. Thus, a large but restricted repertoire of p44 hypervariable sequences exists in A. phagocytophilum strains in the Northeastern United States.
Infection and Immunity 03/2004; 72(2):659-66. DOI:10.1128/IAI.72.2.659-666.2004 · 3.73 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: An important variable in determining the vectorial capacity of mosquito species for arthropod-borne infections is the degree of contact of the vector and the vertebrate reservoir. This parameter can be estimated by examining the host-feeding habits of vectors. Serological and polymerase chain reaction based methods have been used to study the host-feedings patterns of 21 mosquito species from New York, New Jersey, and Tennessee, 19 of which previously have been found infected with West Nile virus. Mammalophilic mosquito species in New Jersey and New York fed primarily upon white-tailed deer, while those from Memphis, Tennessee, fed mainly upon domestic dogs. A total of 24 different avian host species were detected among the avian-derived blood meals. American Robin, Northern Cardinal, Northern Mockingbird, Tufted Titmouse, and Brown-headed Cowbird were common avian hosts, while blood meals derived from the American Crow were relatively rare. Although the majority of common host species were potentially among the most abundant birds at each location, the proportion of blood meals from the most commonly fed upon avian species was greater than was predicted based upon the likely abundance of these species alone. These findings suggest that vector species for West Nile virus may preferentially feed upon certain avian hosts.
[Show abstract][Hide abstract] ABSTRACT: The density of spirochetes in field-collected or experimentally infected ticks is estimated mainly by assays based on microscopy. In this study, a real-time quantitative PCR (qPCR) protocol targeting the Borrelia burgdorferi-specific recA gene was adapted for use with a Lightcycler for rapid detection and quantification of the Lyme disease spirochete, B. burgdorferi, in field-collected Ixodes scapularis ticks. The sensitivity of qPCR for detection of B. burgdorferi DNA in infected ticks was comparable to that of a well-established nested PCR targeting the 16S-23S rRNA spacer. Of the 498 I. scapularis ticks collected from four northeastern states (Rhode Island, Connecticut, New York, and New Jersey), 91 of 438 (20.7%) nymphal ticks and 15 of 60 (25.0%) adult ticks were positive by qPCR assay. The number of spirochetes in individual ticks varied from 25 to 197,200 with a mean of 1,964 spirochetes per nymphal tick and a mean of 5,351 spirochetes per adult tick. No significant differences were found in the mean numbers of spirochetes counted either in nymphal ticks collected at different locations in these four states (P = 0.23 by one-way analysis of variance test) or in ticks infected with the three distinct ribosomal spacer restriction fragment length polymorphism types of B. burgdorferi (P = 0.39). A high degree of spirochete aggregation among infected ticks (variance-to-mean ratio of 24,877; moment estimate of k = 0.279) was observed. From the frequency distribution data and previously published transmission studies, we estimated that a minimum of 300 organisms may be required in a host-seeking nymphal tick to be able to transmit infection to mice while feeding on mice. These data indicate that real-time qPCR is a reliable approach for simultaneous detection and quantification of B. burgdorferi infection in field-collected ticks and can be used for ecological and epidemiological surveillance of Lyme disease spirochetes.
[Show abstract][Hide abstract] ABSTRACT: The seasonal occurrence and abundance of a newly introduced mosquito in the United States, Ochlerotatus (Finlaya) japonicus (Theobald), are reported for Westchester and Putnam Counties in southern New York State. Adult mosquitoes were sampled at 39 sites distributed throughout the two counties. CDC (Centers forDisease Control and Prevention) light traps (2,107 trap nights) and gravid traps (1,813 trap nights) were used to collect a total of 44,428 mosquitoes from May through October 2000. Oc. japonicus was found at 97.4% of sites sampled and accounted for 9.8% of all specimens collected. Oc. japonicus was recovered from 1.5% (n = 326) of the light trap collections and 18.1% (n = 4,026) of the gravid trap collections. Although gravid traps collected significantly more specimens than light traps, the seasonal activity patterns measured by each trap type were congruent. In all, 30 mosquito species were collected. Unlike other Ochlerotatus or Aedes species, Oc. japonicus was collected throughout the study, indicating a broad seasonal activity period. There was significant regional variation in Oc. japonicus abundance, with higher trap densities occurring in the northern-most trapping sites. This study demonstrates that Oc. Japonicus is established in southern New York State.
Journal of Medical Entomology 12/2002; 39(6):920-5. DOI:10.1603/0022-2585-39.6.920 · 1.95 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Mosquitoes and wild birds were collected from three sites near locations in the New York City metropolitan area where single, West Nile (WN) virus-positive dead birds were found early in the 2000 transmission season. The mosquitoes were tested for the presence of infectious virus with a Vero cell culture assay and for WN viral RNA by using reverse transcriptase-polymerase chain reaction (RT-PCR) protocols. Serum samples from wild birds were tested for the presence of neutralizing antibodies against WN virus. Infectious WN virus and WN viral RNA were found in Culex species adult mosquitoes from each of the three sites, and a seropositive hatch-year house sparrow (Passer domesticus) was found in one of the three sites. Molecular techniques used to identify the species in the positive mosquito pools found that most of the pools contained a combination of Culex pipiens and Cx. restuans. The minimum infection rate in Culex species mosquitoes from the sites ranged from 0.2 to 6.0 per 1,000 specimens tested. The results demonstrated that, at least early in the transmission season, detection of a WN virus-positive dead bird indicates a local WN virus transmission cycle. This information is valuable in focusing subsequent surveillance and vector management programs. In addition, the RT-PCR procedure for detecting WN viral RNA in mosquito pools detected more positive pools than did the Vero cell plaque assay.
The American journal of tropical medicine and hygiene 12/2002; 67(5):492-6. · 2.70 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: It is unclear whether antimicrobial treatment after an Ixodes scapularis tick bite will prevent Lyme disease.
In an area of New York where Lyme disease is hyperendemic we conducted a randomized, double-blind, placebo-controlled trial of treatment with a single 200-mg dose of doxycycline in 482 subjects who had removed attached I. scapularis ticks from their bodies within the previous 72 hours. At base line, three weeks, and six weeks, subjects were interviewed and examined, and serum antibody tests were performed, along with blood cultures for Borrelia burgdorferi. Entomologists confirmed the species of the ticks and classified them according to sex, stage, and degree of engorgement.
Erythema migrans developed at the site of the tick bite in a significantly smaller proportion of the subjects in the doxycycline group than of those in the placebo group (1 of 235 subjects [0.4 percent] vs. 8 of 247 subjects [3.2 percent], P<0.04). The efficacy of treatment was 87 percent (95 percent confidence interval, 25 to 98 percent). Objective extracutaneous signs of Lyme disease did not develop in any subject, and there were no asymptomatic seroconversions. Treatment with doxycycline was associated with more frequent adverse effects (in 30.1 percent of subjects, as compared with 11.1 percent of those assigned to placebo; P<0.001), primarily nausea (15.4 percent vs. 2.6 percent) and vomiting (5.8 percent vs. 1.3 percent). Erythema migrans developed more frequently after untreated bites from nymphal ticks than after bites from adult female ticks (8 of 142 bites [5.6 percent] vs. 0 of 97 bites [0 percent], P=0.02) and particularly after bites from nymphal ticks that were at least partially engorged with blood (8 of 81 bites [9.9 percent], as compared with 0 of 59 bites from unfed, or flat, nymphal ticks [0 percent]; P=0.02).
A single 200-mg dose of doxycycline given within 72 hours after an I. scapularis tick bite can prevent the development of Lyme disease.
New England Journal of Medicine 08/2001; 345(2):79-84. DOI:10.1056/NEJM200107123450201 · 55.87 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: An outbreak of encephalitis due to West Nile (WN) virus occurred in New York City and the surrounding areas during 1999. Mosquitoes were collected as part of a comprehensive surveillance program implemented to monitor the outbreak. More than 32,000 mosquitoes representing 24 species were tested, and 15 WN virus isolates were obtained. Molecular techniques were used to identify the species represented in the WN virus-positive mosquito pools. Most isolates were from pools containing Culex pipiens mosquitoes, but several pools contained two or more Culex species.
[Show abstract][Hide abstract] ABSTRACT: Estimates of absolute density were determined over a 5-yr period (1990-1994) for a population of Ixodes scapularis Say located in Westchester County, NY, by mark-release-recapture (nymphs and adults) and removal (larvae) methods. Density estimates for larvae ranged from 5.2 to 16.5/m2 and averaged 11.5/m2. Values for nymphs varied as much as fourfold among successive years, ranging from 0.5 to 2.3/m2 and averaging 1.2/m2, whereas adult density ranged from 0.3 to 0.4/m2, averaging 0.33/m2. Natural mortality of nymphs and adults was measured in experimental cages during population estimation periods, and indicated that survival declined linearly over the short-term and did not significantly influence estimates. Drag sampling efficiency, the proportion of the estimated population obtained in a single sample, averaged 6.3% among all stages. Efficiency was not significantly different among stages and was independent of tick density within a given life stage. The population estimation techniques employed in this study are well suited for use with I. scapularis and can provide data that offer insights into mortality patterns in individual populations.
Journal of Medical Entomology 05/2000; 37(3):357-63. DOI:10.1603/0022-2585(2000)037[0357:EPSADS]2.0.CO;2 · 1.95 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Understanding the role that nymphal and female ticks, Ixodes scapularis , have in the epidemiology of Lyme disease is essential to the development of successful prevention programs. In this study, the authors sought to evaluate the seasonal and annual relations between tick densities and patients ≥16 years of age diagnosed with erythema migrans (EM), the rash associated with early Lyme disease. Ticks were collected weekly by drag sampling throughout most of the year from 1991 to 1996 in Westchester County, New York. The number of EM cases was based on patients diagnosed at the Westchester County Medical Center using Centers for Disease Control and Prevention (CDC) criteria. No patients with EM were diagnosed from January through April, when only adult ticks were active. Correlation analysis between monthly tick densities and EM incidence was significant for nymphs ( r = 0.87, p < 0.01), but not for adult ticks ( r = −0.57, p > 0.05). There was a strong, although not significant, correlation between peak annual number of patients with EM and peak nymphal tick abundance ( r = 0.76, p = 0.08). These data indicate that bites from adult I. scapularis only rarely result in Lyme disease, and that annual nymphal tick abundance determines exposure. This suggests that annual fluctuations in Lyme disease case numbers are largely due to natural changes in tick abundance and, therefore, that control of nymphal I. scapularis should be a major component of Lyme disease prevention efforts. Am J Epidemiol 1999; 149: 771–6.
American Journal of Epidemiology 05/1999; 149(8). DOI:10.1093/oxfordjournals.aje.a009886 · 5.23 Impact Factor