Previous Projects
| POPULATION GENETICS OF IXODES SCAPULARIS | |
| Evaluating the population genetics of a vector species allows inferences to be drawn about its ecology (e.g., population dynamics, dispersal rates and mechanisms) and its evolutionary history. Moreover, population genetics also provides tools for establishing the nature and evolutionary history of the vector's association with the transmitted pathogens. Previous population genetic studies for I.scapularis suggest that genetic structure exists on a continental scale, but often small sample sizes and few genetic markers were used. We are interested in increasing power and resolution for a more detailed analysis and to enable detection of genetic structure at smaller geographic scales. | |
| THE EFFECT OF FEEDING ON PATHOGEN DISTRIBUTION IN IXODES SCAPULARIS | |
| Ticks (Ixodes scapularis) removed from hunter-killed deer are frequently used by health agencies to determine the prevalence of tick borne pathogens in local I. scapularis populations. However, experiments have shown that the prevalence of infection for the Lyme disease spirochete (Borrelia burgdorferi) decreases among ticks feeding upon deer providing an underestimate of prevalence compared to field-collected ticks which indicate the risk of human infection. The reasons for this discrepancy are unclear and we are examining the fate of tick-borne pathogens during the process of feeding. | |
| Engorged (blood-fed) adult, female ticks collected from deer in areas endemic for both Lyme disease and Anaplasma phagocytophilum are dissected and tested by polymerase chain reaction (PCR) to determine if feeding effects the concentration and/or location of these pathogens within the tick. Tick preparations are divided into two groups, whole ticks and salivary glands. Blood-fed ticks removed from deer are compared with flat (unfed) ticks collected from the field at the same locations. The data obtained from blood-fed ticks are compared with data from flat ticks to determine if blood inhibits PCR detection or if the Lyme disease spirochete leaves the tick during feeding. Anaplasma (HGE) is similarly assayed for comparison with B. burgdorferi. | |
| POPULATION BIOLOGY OF BORRELIA BURGDORFERI | |
| For B. burgdorferi, I. scapularis ticks and various vertebrates alternately serve as hosts, but vertebrate species vary in their reservoir competency (i.e., the ability to become infected and to infect vectors). Hence, vertebrate species composition may affect the relative abundance of B. burgdorferi as well as its genetic diversity, if there is differential survival of B. burgdorferi strains among vertebrate species. | |
| In a large-scale field experiment, we have manipulated the vertebrate species composition by vaccinating white-footed mice, a major reservoir host, against B. burgdorferi and are interested in seeing how the manipulation affects B. burgdorferi abundance and genetic diversity. Vaccination simulates the replacement of white-footed mice with another vertebrate species that feeds the tick population just as well as white-footed mice, but that is less reservoir competent. Implicit in this experimental design is the assumption that the white-footed mouse contributes greatly to B. burgdorferi dynamics. We will assay tick and mouse populations for B. burgdorferi infection as well as assess the local B. burgdorferi diversity. Data will help evaluate the relative roles of white-footed mice and alternative hosts (and in a general sense, the role of host community composition) on the abundance and genetic structure of B. burgdorferi in southern CT. Furthermore, this experiment will provide insight into the likely effectiveness of a possible Lyme disease control strategy by intervening in the natural maintenance cycle. This work is done in collaboration with Alan G. Barbour and members of his laboratory at UC Irvine. | |
| REMOTE SENSING AND GIS USED TO IDENTIFY, MAP AND PREDICT REGIONS OF LYME DISEASE RISK | |
| The geographic distribution of Lyme disease in the United States is currently known only from human case report data obtained from the Center for Disease Control’s national surveillance system. The usefulness of these surveillance data is limited by the individual collection and reporting procedures of each state. In addition, the accuracy of Lyme disease case reports suffers from lack of detection, under-reporting, and misclassification of cases, due to variable symptoms and inconsistent serology tests. There exists a great need to improve this information base to better define the geographic distribution of risk by identifying counties that report human cases consistent with ecological parameters indicative of actual risk from potentially infectious tick bites. | |
| We have developed a preliminary Lyme disease risk map using ecological parameters predictive of entomologic risk. The risk map was compiled on a county scale with ArcView, a GIS software program. The layers describing risk by county include data on: CDC human case reports (1994-97), modified (focal sum smoothed) distribution of the tick vector (Ixodes scapularis), ratio of non-competent (reptiles) to total hosts for the immature stages of the tick vector. Expert decision rule was applied to construct the risk classification. A map was constructed which assigns one of four risk classifications to each of the 3,140 U.S. counties. Major regions of risk were identified in the Northeast and the upper Midwest. | |
| For additional methods and information on the National Lyme disease risk map visit the CDC home page, Spot-light on Lyme disease (note prevention and control). | |
| ELUCIDATING THE POPULATION DYNAMICS OF A VECTOR-BORNE INFECTIONS DISEASES: A POPULATIONS AND COMMUNITY LEVEL APPROACH | |
| This project is designed to identify the roles of host and tick densities and host species composition on the infection prevalence of Borrelia burgdorferi in nature. Field experiments include manipulating the average reservoir competence of a local vertebrate host community at field sites in Connecticut to determine the effect of host species composition on the infection prevalence of Borrelia burgdorferi in the deer tick vector. | |
| Field surveys in Connecticut and Georgia will explore the role of vertebrate host community composition in regulating spirochete activity in areas with naturally high and low prevalences. Laboratory experiments will compare the reservoir competence of important host species and explore vector competence in alternative tick species. The results of these experiments will be used to develop a model to simulate spirochete activity under different ecological conditions. | |
| SYSTEMATIC REVISION OF THE NEARCTIC AND NEOTROPICAL AMBLYOMMA SPP. | |
| A prerequisite to study ticks and tick transmitted diseases is the development of rapid identification tools not only for the pathogens, but also for the vectors. Taxonomic keys are not available for all stages of ticks and, when they exist, they are not easily used by untrained eyes. It is therefore important to develop alternative molecular tools for the identification of tick taxa, at the generic, specific and sub-specific level. Different sets of molecular markers have been developed and are currently used for the systematic characterization, by PCR-RFLP and PCR-SSCP, of alcohol preserved collections of ticks for which taxonomic keys are not available. These tools have been applied to the study of the Nearctic and Neotropical Amblyomma species, but can be adapted to the systematic identification of any other genera/species of ticks. Moreover, the sequenced amplified markers produced large datasets for the study of tick phylogeny, which is an essential step toward a better understanding of the evolutionary history of ticks, their phylogeography, and their association with bacterial, viral and protozoan pathogens. More specifically, tick-borne diseases have largely been ignored in the Neotropical faunal area, where Amblyomma species constitute the predominant tick group. The developed tools will facilitate the study of pathogens transmitted by this group of South-American taxa and of their relationships with the better known North American tick-borne micro-organisms. | |
| EVALUATION OF A GIS-DERIVED MODEL FOR PREDICTING LYME DISEASE RISK ON RESIDENTIAL PROPERTIES IN WESTCHESTER COUNTY, NY | |
| Two population samples, totaling 1300 households, were sent a questionnaire asking for information relevant to Lyme disease epidemiology (e.g., history of tick bites, diagnoses of Lyme disease, etc.) and ecology (e.g., proximity of woodland, presence of deer, etc.) concerning their household. GIS software was used to find the geographic references of the sample households, which, in turn, enabled us to geo-locate them on Thematic Mapper satellite images. The Lyme disease risk of each property then was assessed according the model, which is based on satellite image analyses of area landscape features (e.g., ground-cover type, soil moisture level, etc.) Finally, a sub-sample of properties identified as "high risk" and "low or no risk", according to the model, were surveyed for ticks. Evaluating the model involves comparing risk as determined by the model with the questionnaire and tick sampling results. | |
| DETERMINATION OF RESERVOIR HOSTS FOR TICK-BORNE ZOONOSES |
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| Understanding the natural cycles of tick-borne zoonotic pathogens, especially identification of their natural animal reservoirs, is a critical step in understanding their epidemiology. This in turn is an important step towards controlling their transmission. Ixodes scapularis is a vector of several zoonotic pathogens. Two of these, the Lyme disease spirochete and Anaplasma phagocytophilum, are arguably the most important vector-borne pathogens in the US today. We have proposed to develop molecular techniques for identification of reservoir hosts of the most easily collected tick life stages, host seeking individuals. The previous feeding history of these individuals determines their potential for infection with disease agents. Although their infection status can be determined, no method has yet been implemented that can identify the prior host of this life stage. We have proposed a method for identification of hosts by PCR amplification of host specific markers from remnants of the blood meal in the gut of the tick and slot blotting of amplicons against host specific probes. | |
| CONTRIBUTION OF BIRDS AS RESERVOIRS FOR ANAPLASMA |
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| To determine the reservoir competency of birds for Anaplasma phagocytophilum, we have analyzed DNA extracted from archived and preserved larval Ixodes scapularis that have fed on several species of birds by PCR. Initial results have shown these larvae to test positive for the agent of A.phagocytophilum, indicating that larvae have acquired the organism while taking their first blood meal. Engorged larvae from several species of birds which commonly host I.scapularis have including Common Yellowthroats, American Robins, and Northern Cardinals and ticks fed on these specieshave tested positive by PCR. This information may explain the unique distribution of A. phagocytophilum in nature, and indicates that more than one reservoir host is responsible for maintaining it. | |
| A CLIMATE-BASED MODEL PREDICTS THE SPATIAL DISTRIBUTION OF THE LYME DISEASE VECTOR IXODES SCAPULARIS IN THE UNITED STATES |
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| An understanding of the spatial distribution
of the black-legged tick, Ixodes scapularis, is a fundamental component
in assessing human risk for Lyme disease in much of the United States.
Though a county level vector distribution map exists for the United States,
its accuracy is limited by arbitrary categories of its reported presence.
It is unknown whether reported positive areas can support established
populations and whether negative areas are suitable for established populations.
The steadily increasing range of I. scapularis in the US suggests
that all suitable habitats are not currently occupied. Therefore, we developed
a spatially predictive logistic model for I. scapularis in the
conterminous US to improve the previous vector distribution map. We used
ground-observed environmental data to predict the probability of established
I. scapularis populations. The autologistic analysis showed that
maximum, minimum and mean temperature, as well as vapour pressure significantly
contribute towards population maintenance with an accuracy of 95% (P<0.0001).
A cutoff probability for habitat suitability was assessed by sensitivity
analysis and was used to reclassify the previous distribution map.
..The spatially modeled relationship between I. scapularis presence and large-scale environmental data provides a robust distribution model that serves to reveal essential environmental determinants of habitat suitability, predicts emerging areas of Lyme disease risk and generates the future pattern of I. scapularis across the US. |
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| ISOLATION AND CULTIVATION OF EHRLICHIA FROM NATURAL POPULATIONS |
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| Adult Ixodes scapularis ticks are field-collected from sites in the U.S. where cases of Anaplasma phagocytophilum have been reported. Ticks are fed upon animals in our laboratory an attempt to culture Anaplasma isolates from blood. Animals are monitored by serology, blood examination, and by polymerase chain reaction (PCR) to detect infection. At the same time, uninfected ticks are placed on the animals to obtain infection and these infected ticks will later be used for further experiments. New isolates of Ixodes-borne Ehrlichia from various sites in the U.S. are compared for infectivity and virulence in laboratory animal models. Cultures are compared for genetic similarity and antigenic reactivity with human and animal sera at collaborating laboratories. | |
| SURVEILLANCE FOR TICK-BORNE PATHOGENS BY CANINE SEROLOGY | |
| This project is designed to develop accurate methods for determining the geographic distribution of tick-borne pathogens transmissible to humans. Increases in the abundance and range of the vector tick Ixodes scapularis, and consequential emergence of Lyme disease and human granulocytic ehrlichiosis have raised concerns of public health agencies in the Northeast and upper Midwest. Canines are generally more exposed to Ixodes scapularis bites than humans and are also susceptible to infection with agents of both diseases. Serological assays are conducted on canine serum randomly collected by collaborating veterinarians. The information obtained is used to predict human exposure to tick-borne pathogens in a variety of ecological and social settings and provides prevalence data for both Lyme disease and granulocytic ehrlichiosis. | |
| ECOLOGY OF LYME DISEASE AND ANAPLASMA PHAGOCYTOPHILUM IN CONNECTICUT | |
| Pathogens of both Lyme disease (Borrelia burgdorferi) and A. phagocytophilum are prevalent in Ixodes scapularis ticks and in small rodents in Connecticut. Natural cycles of these agents in their natural foci, as well as mechanisms regulating coexistence of the two pathogens in the transmission between ticks and their hosts will be closely studied. To gather data for the study, we will collect ticks and trap mammals in various locations in Connecticut. All stages of ticks will be collected from vegetation throughout the period of their activity - April through October – and examined for the prevalence of infection with each pathogen. Simultaneously, small and medium-sized animals will be trapped repeatedly in the same locations. Samples of blood, serum, and skin will be collected from each animal for later examination, and animals will be released at the site of capture. A comparison of the infection rates between mammals and different life stages of ticks, between different sites, and between successive years will allow us to assess the intensity of the transmission in natural cycles. | |
| USDA NORTHEARN REGIONAL DEER TICK CONTROL PROJECT |
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| A multi-center project was begun in
1997 to demonstrate the feasibility of large area control of the deer
tick vector of Lyme disease, human granulocytic ehrlichiosis, and human
babesiosis, by treating white-tailed deer, an obligatory host species,
with acaricide. USDA- patented device designed to passively apply acaricide
at deer
feeding stations has been sucessfully used to control another tick species in Texas with similar dependency upon deer. Twenty-five of these stations have been installed in residential communities where Lyme disease is hyperendemic in five states: New York, New Jersey, Connecticut, Rhode Island, and Maryland. Station maintenance and tick population monitoring are being conducted by collaborating scientists at each location. If successful, this approach could be the focus of community-based efforts to control vector tick populations over large areas that would reduce or eliminate the risk of tick-borne infection to humans and companion animals. A multi-center project was begun in 1997 to demonstrate the feasibility of large area control of the deer tick vector of Lyme disease, human granulocytic ehrlichiosis, and human babesiosis, by treating white-tailed deer, an obligatory host species, with acaricide. |
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| EVALUATION OF THE USDA NORTHEAST AREA-WIDE TICK CONTROL PROJECT BY META-ANALYSIS |
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| An initiative was started in 1997 to demonstrate that a tick control strategy focused on white-tailed deer, the major hosts for adult Ixodes scapularis ticks, could reduce human risk for Lyme disease and other tick-borne diseases in endemic communities of the Northeastern USA. White-tailed deer were treated with Point-Guard (2% amitraz) using the USDA-ARS patented ‘4-poster’ device. Questing nymphal I. scapularis ticks were sampled in control and treatment sites in Rhode Island, Connecticut, New York, New Jersey, and Maryland in five concurrent studies to assess the efficacy of treatment. A meta-analysis was constructed with tick collection data from 1998–2002 to derive an overall assessment of the project’s success to date. The meta-analysis accounts for differences in sample size, effect variance, sampling method, and season. The meta-analysis shows an increasing trend of efficacy for the control strategy within treatment sites of 1.28 km radius, demonstrating that a high level of tick control can be achieved by treating white-tailed deer. | |
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| TRANSMISSION AND MAINTENANCE OF ANAPLASMA PHAGOCYTOPHILUM IN THE NORTHEAST | |
| The goal of this project is to define the role of three species of tick (black-legged tick Ixodes scapularis, American dog tick Dermacentor variabilis, the lone star tick Amblyomma americanum), in the transmission of A. phagocytophilum. The objectives of the study are to understand the course of granulocytic Anaplasma infection in ticks; to evaluate the role of three species of tick as vectors of granulocytic ehrlichiosis; to estimate the prevalence of natural granulocytic Anaplasma infection in ticks at selected sites; and to evaluate the role of mon mammal and bird species in the northeast as reservoirs for granulocytic Anaplasma. | |
| RESERVOIR COMPETENCE OF SMALL AND MEDIUM-SIZED MAMMALS FOR ANAPLASMA PHAGOCYTOPHILUM | |
| Small and medium-sized animal species are live-trapped in areas with a high prevalence of Anaplasma in questing ticks. Prior to release, chipmunks, skunks, raccoons, and white-footed mice are held for several days in the laboratory to allow all naturally attached ticks to feed to repletion. Engorged ticks are collected, allowed to molt to the next stage, identified by the species and stage, and tested by PCR for infection with B. burgdorferi and Anaplasma. This allows assessment of the infectivity of individual animals for feeding ticks in an effort to determine which mammalian species are infected with A. phagocytophilum and could serve as potential reservoirs of the organism in nature. | |
| NON-RICKETTSIEMIC TRANSMISSION OF ANAPLASMA PHAGOCYTOPHILUM BETWEEN COFEEDING TICKS | |
| Transmission of a pathogen between infected and uninfected ticks feeding simultaneously may be an important mode of perpetuation of the natural transmission cycle. Particularly so, if the infection caused by a pathogen in a susceptible host is transient and followed by a strong immune response, as in case of murine infection with Anaplasma. Groups of naive and immune mice will be infested simultaneously with Anaplasma- infected nymphal ticks and uninfected I. scapularis larvae to evaluate the possibility and efficiency of transmission of the agent of Anaplasma between cofeeding ticks. | |
| INTERACTION BETWEEN PATHOGENS OF LYME DISEASE AND ANAPLASMA PHAGOCYTOPHILUM | |
| Pathogens of both Lyme disease (Borrelia burgdorferi) and Anaplasma are transmitted by the same species of ticks (Ixodes scapularis), and often co-exist within the vector population. A certain proportion of ticks, as well as their vertebrate hosts, is usually infected with two pathogens simultaneously. Pathogens may be transmitted independently, or they may interact in different ways supporting or weakening transmission of one another. We assess modes of interaction between Borrelia and Anaplasma in both vectors and vertebrate hosts by comparing the efficiency of transmission when ticks and rodents are infected with either one pathogen or with both pathogens simultaneously. | |
| 1) Groups of white-footed mice (natural hosts for immature ticks) have been infected with Borrelia and/or Anaplasma via tick bites. One group was fed upon by nymphal ticks infected with Borrelia only, the other – with Anaplasma only, and the rest of mice were infested with ticks infected with both pathogens. Larval ticks will be fed upon those mice weekly for the next 2 months. After ticks molt into the next stage, they will be tested for the presence of both pathogens by PCR. The efficiency of transmission from mice to ticks will be measured as a percentage of ticks that acquired one, or the other, or both pathogens with their blood-meal. Differences in the efficiency of transmission from mice infected with either pathogen versus mice infected with 2 pathogens simultaneously will reflect pathogen interaction in a reservoir host. | |
| 2) Individual nymphal ticks infected with either B. burgdorferi, or A. phagocytophilum, or both have been fed upon white-footed mice. Two weeks later, uninfected I. scapularis larvae will be placed on these mice. Engorged larvae will be tested by PCR for the presence of infection. The efficiency of transmission from a tick to a host will be measured as a percentage of mice that acquired one, or the other, or both pathogens from nymphs and infected feeding larvae. Differences in the efficiency of transmission between ticks infected with either pathogen and ticks infected with 2 pathogens simultaneously will reflect pathogen interaction in a vector. | |
| 3) Groups of white-footed mice infected with B. burgdorferi have been fed upon by cohorts of either uninfected nymphal ticks, or nymphs infected with A. phagocytophilum. When engorged ticks molt to the adult stage, they will be tested by PCR for the presence of both pathogens. Effect of preexisting Anaplasma infection in ticks on acquisition of Borrelia from an infected host will be assessed as the difference in the prevalence of B. burgdorferi between groups of ticks previously uninfected and infected with A. phagocytophilum. Similarly, mice infected with A. phagocytophilum have been infested with nymphs either uninfected or infected with B. burgdorferi to assess effect of preexisting Borrelia infection in ticks on acquisition of A. phagocytophilum. | |
| POPULATION SURVIVAL UNDER ENVIRONMENTAL STRESS | |
| This project was designed to measure fitness of Ixodes scapularis ticks and the effects of Anaplasma infection on their survival. Anaplasma phagocytophilum used was isolated from a sample in Spooner, Wisconsin. Ixodes scapularis are normally kept at 22C and >95% relative humitidy. Two populations of I. scapularis nymphs were used in this experiment. One population was fed as larvae on uninfected mice. The second population was fed as larvae on mice that had been fed on by infected nymphs. These mice had also tested seropositive in an IFA assay. These populations were put in 86-88% relative humidity to test their relative abilities to survive environmental stress. | |
| ANALYSIS OF HOST ACTIVITY AND TICK DROP-OFF TIME | |
| Ticks tend to drop from their hosts at certain times of day. Drop-off time depends, to some extent, on the host species. This project examines whether host activity triggers tick drop-off. To answer this question, the activity of the host was altered using two different behavioral drugs. Ticks were then collected from the host at three hour intervals during the day and monitored by by time-lapse video. The data is currently being analyzed to see if the ticks on drug-altered mice tended to drop at different times than the ticks on the control mice. The ways in which the drop off time of ticks is controlled can help us to understand how the tick is distributed in nature. | |
| RISK MAPPING OF WEST NILE VIRUS IN NEW YORK CITY | |
| We determined the distribution of human risk for West Nile virus by spatial analysis of the case distribution in the New York City area using remote sensing (RS) and geographic information system (GIS) technologies. Cluster analysis revealed the presence of a statistically significant grouping of cases, which also indicates the area of probable virus introduction. Within the cluster, habitat suitability for potentially infective adult mosquitoes was measured by the amount of vegetation cover using satellite imagery. Logistic regression analysis revealed satellite derived vegetation abundance to be significantly and positively associated with the presence of human cases. The logistic model was used to estimate the spatial distribution of human risk for West Nile virus throughout New York City. Accuracy of the resulting risk map was cross-validated using virus positive mosquito sample sites. These new epidemiological methods permit rapid entry point identification and spatial prediction of human risk of infection for introduced vector-borne pathogens. | |
| MODELING RANGE EXPANSION OF IXODES SCAPULARIS IN NORTH AMERICA USING PREDICTED CLIMATE CHANGE | |
| Because of the clear relationship between climate and I scapularis habitat suitability, climate forecasting can be used to predict tick populations in future years. Our logistic model of current habitat suitability provided the basis for forecasting the contribution of climate change in the future patterns of I scapularis establishment throughout North America. Global Climate Models (GCM) forced with changes in greenhouse gas concentrations alone and those forced with greenhouse gas and sulphate aerosol changes resulting from anthropogenic effects were considered. Data on the change of each climate variable from present conditions was acquired for 3 mean 30-year time points: 2020, 2050 and 2080. The logistic model was extrapolated in time according to the different GCM’s and used to predict the future probabilities of establishment for I. scapularis across North America. The final result was a series of habitat suitability maps that provide the expected change in distribution of I. scapularis, clearly defining future areas of Lyme disease risk. | |
| AFRICAN SWINE FEVER * | |
| This research project concentrates on the relationship
between African Swine Fever Virus (ASFV) and its co-evolved arthropod
vector/host the Argasid tick Ornithodoros porcinus porcinus. We are using
molecular virology and viral genetics to identify and study host range
and virulence associated viral genes and to look at the interaction between
the virus and its vector.
We are also interested in the biology and ASFV vector competence of North American species of Ornithodoros. |
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| * Research was Conducted at Plum Island
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