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Adverse moisture events predict seasonal abundance of Lyme disease vector ticks (Ixodes scapularis)

BACKGROUND: Lyme borreliosis (LB) is the most commonly reported vector-borne disease in north temperate regions worldwide, affecting an estimated 300,000 people annually in the United States alone. The incidence of LB is correlated with human exposure to its vector, the blacklegged tick (Ixodes scap...

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Autores principales: Berger, Kathryn A, Ginsberg, Howard S, Dugas, Katherine D, Hamel, Lutz H, Mather, Thomas N
Formato: Online Artículo Texto
Lenguaje:English
Publicado: BioMed Central 2014
Materias:
Acceso en línea:https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3991885/
https://www.ncbi.nlm.nih.gov/pubmed/24731228
http://dx.doi.org/10.1186/1756-3305-7-181
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author Berger, Kathryn A
Ginsberg, Howard S
Dugas, Katherine D
Hamel, Lutz H
Mather, Thomas N
author_facet Berger, Kathryn A
Ginsberg, Howard S
Dugas, Katherine D
Hamel, Lutz H
Mather, Thomas N
author_sort Berger, Kathryn A
collection PubMed
description BACKGROUND: Lyme borreliosis (LB) is the most commonly reported vector-borne disease in north temperate regions worldwide, affecting an estimated 300,000 people annually in the United States alone. The incidence of LB is correlated with human exposure to its vector, the blacklegged tick (Ixodes scapularis). To date, attempts to model tick encounter risk based on environmental parameters have been equivocal. Previous studies have not considered (1) the differences between relative humidity (RH) in leaf litter and at weather stations, (2) the RH threshold that affects nymphal blacklegged tick survival, and (3) the time required below the threshold to induce mortality. We clarify the association between environmental moisture and tick survival by presenting a significant relationship between the total number of tick adverse moisture events (TAMEs - calculated as microclimatic periods below a RH threshold) and tick abundance each year. METHODS: We used a 14-year continuous statewide tick surveillance database and corresponding weather data from Rhode Island (RI), USA, to assess the effects of TAMEs on nymphal populations of I. scapularis. These TAMEs were defined as extended periods of time (>8 h below 82% RH in leaf litter). We fit a sigmoid curve comparing weather station data to those collected by loggers placed in tick habitats to estimate RH experienced by nymphal ticks, and compiled the number of historical TAMEs during the 14-year record. RESULTS: The total number of TAMEs in June of each year was negatively related to total seasonal nymphal tick densities, suggesting that sub-threshold humidity episodes >8 h in duration naturally lowered nymphal blacklegged tick abundance. Furthermore, TAMEs were positively related to the ratio of tick abundance early in the season when compared to late season, suggesting that lower than average tick abundance for a given year resulted from tick mortality and not from other factors. CONCLUSIONS: Our results clarify the mechanism by which environmental moisture affects blacklegged tick populations, and offers the possibility to more accurately predict tick abundance and human LB incidence. We describe a method to forecast LB risk in endemic regions and identify the predictive role of microclimatic moisture conditions on tick encounter risk.
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spelling pubmed-39918852014-04-20 Adverse moisture events predict seasonal abundance of Lyme disease vector ticks (Ixodes scapularis) Berger, Kathryn A Ginsberg, Howard S Dugas, Katherine D Hamel, Lutz H Mather, Thomas N Parasit Vectors Research BACKGROUND: Lyme borreliosis (LB) is the most commonly reported vector-borne disease in north temperate regions worldwide, affecting an estimated 300,000 people annually in the United States alone. The incidence of LB is correlated with human exposure to its vector, the blacklegged tick (Ixodes scapularis). To date, attempts to model tick encounter risk based on environmental parameters have been equivocal. Previous studies have not considered (1) the differences between relative humidity (RH) in leaf litter and at weather stations, (2) the RH threshold that affects nymphal blacklegged tick survival, and (3) the time required below the threshold to induce mortality. We clarify the association between environmental moisture and tick survival by presenting a significant relationship between the total number of tick adverse moisture events (TAMEs - calculated as microclimatic periods below a RH threshold) and tick abundance each year. METHODS: We used a 14-year continuous statewide tick surveillance database and corresponding weather data from Rhode Island (RI), USA, to assess the effects of TAMEs on nymphal populations of I. scapularis. These TAMEs were defined as extended periods of time (>8 h below 82% RH in leaf litter). We fit a sigmoid curve comparing weather station data to those collected by loggers placed in tick habitats to estimate RH experienced by nymphal ticks, and compiled the number of historical TAMEs during the 14-year record. RESULTS: The total number of TAMEs in June of each year was negatively related to total seasonal nymphal tick densities, suggesting that sub-threshold humidity episodes >8 h in duration naturally lowered nymphal blacklegged tick abundance. Furthermore, TAMEs were positively related to the ratio of tick abundance early in the season when compared to late season, suggesting that lower than average tick abundance for a given year resulted from tick mortality and not from other factors. CONCLUSIONS: Our results clarify the mechanism by which environmental moisture affects blacklegged tick populations, and offers the possibility to more accurately predict tick abundance and human LB incidence. We describe a method to forecast LB risk in endemic regions and identify the predictive role of microclimatic moisture conditions on tick encounter risk. BioMed Central 2014-04-14 /pmc/articles/PMC3991885/ /pubmed/24731228 http://dx.doi.org/10.1186/1756-3305-7-181 Text en Copyright © 2014 Berger et al.; licensee BioMed Central Ltd. http://creativecommons.org/licenses/by/2.0 This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly credited. The Creative Commons Public Domain Dedication waiver (http://creativecommons.org/publicdomain/zero/1.0/) applies to the data made available in this article, unless otherwise stated.
spellingShingle Research
Berger, Kathryn A
Ginsberg, Howard S
Dugas, Katherine D
Hamel, Lutz H
Mather, Thomas N
Adverse moisture events predict seasonal abundance of Lyme disease vector ticks (Ixodes scapularis)
title Adverse moisture events predict seasonal abundance of Lyme disease vector ticks (Ixodes scapularis)
title_full Adverse moisture events predict seasonal abundance of Lyme disease vector ticks (Ixodes scapularis)
title_fullStr Adverse moisture events predict seasonal abundance of Lyme disease vector ticks (Ixodes scapularis)
title_full_unstemmed Adverse moisture events predict seasonal abundance of Lyme disease vector ticks (Ixodes scapularis)
title_short Adverse moisture events predict seasonal abundance of Lyme disease vector ticks (Ixodes scapularis)
title_sort adverse moisture events predict seasonal abundance of lyme disease vector ticks (ixodes scapularis)
topic Research
url https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3991885/
https://www.ncbi.nlm.nih.gov/pubmed/24731228
http://dx.doi.org/10.1186/1756-3305-7-181
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