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

Particle and Fibre Toxicology

Thomas N Mather²  Lutz H Hamel³  Katherine D Dugas²  Howard S Ginsberg⁴  Kathryn A Berger¹ 

[1] Present address: Faculty of Veterinary Medicine, University of Calgary, GIS Lab TRW 2D28, 3280 Hospital Drive NW, T2N 4Z6 Calgary, AB, Canada;Center for Vector-Borne Disease, University of Rhode Island, 02881 Kingston, RI, USA;Department of Computer Science and Statistics, University of Rhode Island, 02881 Kingston, RI, USA;Department of Plant Sciences and Entomology, University of Rhode Island, 02881 Kingston, RI, USA

关键词: Survival;    Tick activity;    Relative humidity;    Ixodes scapularis;   

Others  :  807262
DOI  :  10.1186/1756-3305-7-181

 received in 2013-12-10, accepted in 2014-04-08,  发布年份 2014

【 摘 要 】

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.

【 授权许可】

   
2014 Berger et al.; licensee BioMed Central Ltd.

【 图 表 】

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