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Forecasting Tick-Borne Disease

Lead Scientist(s): Dr Richard S Ostfeld Dr Shannon L LaDeau

With support from the US Department of Defense’s Strategic Environmental Research and. Development Program (SERDP), we have undertaken a five-year study looking at the effects of climate change on blacklegged ticks – the primary vector for diseases like Lyme disease, anaplasmosis, babesiosis, and Powassan virus.

Ticks have three active life stages: larva, nymph, and adult. Ticks take one blood meal at each life stage.  This research is examining how weather influences survival at each stage. The project focuses on three field sites located on US military bases: West Point in southern New York, Fort Drum in northern New York, and Camp Lejeune in coastal North Carolina. The bases occur along a range of latitudes, with distinct climate conditions. We are monitoring tick survival, reproduction, and feeding behavior – along with climate data – at each site.

At each of the three field sites, we are deploying ticks annually – including fed and unfed samples of each life stage – in outdoor containers to monitor survival given the particular conditions of the site. A ‘tick container’ consists of a soil core with leaf litter on top and that is placed inside a fine mesh fabric that ticks cannot penetrate.

Each life stage of tick is deployed at a specific time of year – when that life stage is most active in nature: nymphs in spring, larvae in late summer, and adults in the fall. We are deploying four ‘rounds’ of ticks over the 4-year data collection phase of the project.

For the unfed ticks, we are monitoring survival and questing activity. For the fed ticks, we are interested in two factors beyond survival: (1) molting success – the ability of fed larval and nymphal ticks to transition from one life stage to the next and (2) oviposition, or egg-laying, success among fed female adult ticks.

Microclimate data, including the temperature and relative humidity in the tick containers, are recorded. By exposing ticks of all life stages to ambient conditions at three distinct latitudes, we can better understand the impact of current climatic conditions and specific weather events such as extreme heat and changes in freeze-thaw cycles on tick survival and population growth.

A laboratory study using programmable incubators has already investigated how warming amplifies the Lyme disease pathogen Borrelia burgdorferi – in terms of the pathogen’s survival within the tick, as well as the tick’s ability to transmit the pathogen to a mouse host. The experimental phase of this study is complete; pathogen analysis is forthcoming.

The project will also include an experimental component in which ticks from all three sites are exposed to artificially-warmed conditions – which will be created using warming cables placed in the soil surrounding the tick containers – to understand the impact of warmer future climates on blacklegged tick populations.

Data from all phases of the project will be used to develop models to understand the impact of changing climatic conditions on blacklegged tick populations and Lyme disease risk in humans. These models could help forecast future disease risk and help mitigate tick-borne illness.