# Time to Emergence of the Lyme Disease Pathogen in Habitats of the Northeastern U.S.A

## TL;DR

This study estimates how long it takes for the Lyme disease pathogen to become established in new areas of New Hampshire, based on tick life cycles and host interactions.

## Contribution

The study introduces a combined modeling approach to estimate the time to endemicity of Lyme disease in new habitats.

## Key findings

- The time to reach Borrelia endemicity in New Hampshire ranges from 8 to 20 years.
- Susceptible tick host populations strongly influence the time to endemicity.
- Temperature, infection probabilities, and host populations are key factors identified through sensitivity analysis.

## Abstract

Lyme disease is contracted by humans through the bite of a black-legged tick. The pathogen is maintained in tick populations through reservoirs of tick hosts in the wild, including pathogen hosts such as the white-footed mouse and mobile tick hosts such as the white-tailed deer. The pathogen may be introduced into a new location by the arrival of infected ticks, but it may take years to establish at endemic levels. A process-based model describes the tick life cycle, host interaction, and disease transmission. A statistical model predicts the populations of deer and mice across New Hampshire. We combine both types of models to estimate how long it takes this disease to establish in the environment and to identify major contributing factors.

Ticks carry a range of pathogens, the best known of which causes Lyme disease, prevalent in the northeastern United States. Emerging diseases do not yet consist of a wide range of Lyme diseases, raising the question of how long it takes for a newly introduced tick-borne disease to establish itself. The aim of this study was to address this question, with the agent of Lyme disease used as the test case. A prior process-based model of the Ixodes scapularis (Say 1821) life cycle and the transmission of Borrelia burgdorferi (Burgdorfer 1982) between this tick and its various hosts was used to predict the dynamics of disease introduction into a new area. The importance of temperature, infection probabilities, and tick host populations, relative to that of other factors, was established by a global sensitivity analysis using Latin hypercube sampling. The results of those samples were analyzed to determine the time to near-equilibrium. Eight locations in New Hampshire were chosen for high/low temperature, high/low mouse, and high/low deer values. Mammal abundance was estimated by relating the known mammal density from previous studies to a MaxEnt analysis output. The time required to reach Borrelia endemicity in the ticks of New Hampshire ranged from 8 to 20 years in regions where the tick population is viable, with a strong dependency on susceptible tick host populations.