RESEARCH IN PROGRESS
| PROPAGATION OF TICKS |
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| The Vector Biology Laboratory maintains infected and uninfected deer ticks (Ixodes scapularis) for research on Lyme disease and Anaplasma, and as a source of ticks for collaborating laboratories, teaching, studies on vaccine development, pathogen detection methods, and tick biology. | |
| Ticks are maintained by feeding upon laboratory animals (mice, sheep, and rabbits). After 3 to 7 days of feeding ticks will drop from their hosts and accumulate in water pans placed beneath the animal cages. Engorged ticks are removed from the pans, counted, placed into vials, and stored in environmental chambers until molting to the next stage. Ticks are constantly maintained by this process with more than 10,000 eggs, larvae, nymphs, and adult ticks available at any time to support the research activities of the laboratory. | |
| Multiple isolates of both Borrelia burgdorferi and Anaplasma phagocytophilum are also maintained for a variety of studies involving pathogen acquisition, pathogen interaction and the effect of these pathogens on tick feeding and survival. Each isolate is maintained separately by continuous passage through tick vectors and laboratory animals. | |
| Small colonies of other tick species of importance in human and animal disease are also maintained, which include the American dog tick (Dermacentor variabilis), the lone star tick (Amblyomma americanum), and the African tampan (Ornithodorous moubata). | |
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| GENOTYPING OF BORRELIA STRAINS |
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| The study of the natural cycles and the ecology of tick-borne spirochetoses often requires the analysis of large samples of collected tick specimens. PCR, if sensitive enough, is the basic technique for determining prevalence rates in tick populations. The identification of the infecting strains is ideally performed by subsequent sequencing of the amplified product. Sequencing can, however, not be performed on every single positive sample. Alternative methods have been or are currently being developed for the simultaneous detection and specific identification of Borrelia organisms (PCR-SSCP, PCR-RFLP, reverse line blot hybridization). | |
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| TRANSMISSION AND LABORATORY MAINTENANCE OF A NEW BORRELIA SPECIES |
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| A species of Borrelia spirochetes previously unknown from North America has been found by this laboratory to be transmitted by Ixodes scapularis ticks. Phylogenetic analysis of this unknown "New Borrelia" showed it to cluster with the relapsing fever group spirochetes rather than with Lyme disease spirochetes. We are currently investigating studies on the transmission/acquisition of this organism from/to ticks to/from mammalian hosts in the laboratory. Other studies involve field investigations to identify the natural mammalian reservoir, and the natural distribution and frequency of this organism in nature. | |
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| FIELD SURVEILLANCE FOR NEW BORRELIA AND BABESIA |
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| Monitoring the infection rates of nymphal and adult Ixodes scapularis ticks collected from field and residential sites helps public health officials to determine the risk for acquiring a tick-borne disease. The Vector Ecology Laboratory routinely screens ticks collected from field sites and residential areas of interest for Borrelia burgdorferi as well as Anaplasma phagocytophilum. As the range and distribution of I.scapularis changes, and as more pathogens are identified and determined to be transmitted by this tick, field surveillance becomes even more important. Recently we have begun to screen ticks for Babesia microti, a protozoan previously of limited or no occurrence in Connecticut as well as the "new Borrelia" species identified. It is interesting and important to realize that as many as 4 pathogens may be carried and transmitted by an individual tick in the areas where I. scapularis is found. Monitoring the frequency of ticks infected with these pathogens at our field sites may help us to determine if these organisms are maintained individually and if they interact or influence the transmission/acquisition of each other within the host or tick. In addition, we have been able to offer other locales (Hunterdon County, NJ) interested in tracking tick-borne diseases, the opportunity to screen ticks using our laboratory PCR assays. | |
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| TRANSMISSION AND MAINTENANCE OF BABESIA |
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| Babesia microti is an intraerythrocytic protozoan that is transmitted by Ixodes scapularis ticks. This organism often causes a fulminating hemolytic anemia in susceptible animal species as well as humans. In some cases, the disease may become "subclinical" which means it can go undetected for some time; this has most recently caused concern with Babesia contaminated blood or blood blanks and transfusions to imunocompromised individuals. Previously, B.microti had a distribution limited to parts of Rhode Island and Martha’s Vineyard in the Northeast. Recently however, improved surveillance methods have identified foci of infected ticks much further south. Determining how Babesia and other pathogens become dispersed into new areas requires continual field studies and surveillance. In order to better understand the relationship between B. microti and it’s tick vector, we have begun to maintain laboratory colonies of ticks infected with a local isolate of Babesia so that we can conduct transmission, acquisition, and coinfection studies in the laboratory and field and develop a better understanding and predicting its relative occurrence and impact in nature. | |
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| SPATIAL RELATIONSHIPS BETWEEN AND AMONG MOSQUITO VECTORS OF WEST NILE VIRUS: APPLICATION OF SPATIAL STATISTICS, MULTIPLE STEPWISE REGRESSION AND ARTIFICIAL NEURAL NETWORKS |
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| Research in vector ecology suggests that if spatial structure is present, insect count data from traps can be used to estimate densities between sampling sites, identify spatial relationships between insects and landscape features and integrate multiple attributes such as age and sex densities on different spatial scales. | |
| In addition to spatial statistics, other methods such as, cubic spline regression, multiple stepwise linear regression and artificial neural networks (ANN)are applied to mathematically integrate data layers. Hampson-Russell ISMAP and Gamma Design GS+ software is used to do spatial analysis, multiple regression and artificial neural networking. The Vector Ecology Laboratory uses two types of artificial neural networking, Multilayer Feed Forward (MLFN) and Probabilistic Neural Network (PNN). Future research will test these methods on different organisms and at different scales. | |
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| 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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