This Study Deconstructs the Complex Web of Interactions Between Bacteria and Their Environment in Lyme Disease Ecology

This Study Deconstructs the Complex Web of Interactions Between Bacteria and Their Environment in Lyme Disease Ecology

The ability to foresee areas likely to have an outbreak of Lyme disease can be invaluable to public health officials in allocating resources and crafting preventative awareness campaigns. However, the ecology of Lyme disease is intricate, encompassing numerous species of hosts, the disease-transmitting black-legged tick, Borrelia burgdorferi bacterium, and the natural habitats of all these organisms.

The study, which was published in the Journal of Applied Ecology, clarifies the interplay between bacteria and the environment in the etiology of Lyme disease. Tam Tran, who earned her Ph.D. in Penn’s Department of Biology in the School of Arts & Sciences, is leading this investigation into the effects of factors like landscape disturbance and climate on the distribution and abundance of B. burgdorferi. Tran is being advised by Dustin Brisson, a professor in the department, Shane Jensen, an associate professor in the Wharton School, and colleagues from the New York State Department of Health. The end product is an effective analytical model that can accurately forecast the geographic distribution of Lyme disease bacteria, which might be used as a public health tool to reduce the spread of the disease.

“We recognize that Lyme disease poses a rising risk to public health, yet effective solutions remain elusive. The incidence rate keeps rising, “According to Tran, who is currently enrolled in the medical program at Virginia Commonwealth University. Excitingly, “we can forecast where and when there will be higher concentrations of the pathogen in the landscape by knowing how the environment impacts both the tick system and the bacteria.”

Tran, Brisson, Jensen, and colleagues estimated the prevalence of B. burgdorferi by measuring what percentage of black-legged ticks they examined were infected with the bacteria, but they were also interested in what factors influenced B. burgdorferi. Because the contributions of the “environment” in general can be so varied, Tran argues, previous attempts to establish linkages between Lyme disease and environmental variables have yielded mixed, ambiguous, or sometimes even contradictory results.


The research team used data from roughly 19,000 black-legged ticks gathered from hundreds of sites across New York State between 2009 and 2018 to inform their models. They looked studied hundreds of locations spread out over a decade to see if the ratio of infected to uninfected ticks matched up with four types of local environmental factors:

This Study Deconstructs the Complex Web of Interactions Between Bacteria and Their Environment in Lyme Disease Ecology

1) landscape factors such as elevation, fire history, and distance to infrastructure like roads;

2) vertebrate host population sizes, including people, bears, birds, and deer;

3) surveillance conditions including local temperature and humidity at the time of collection as well as the effort devoted to collecting specimens; and

4) climate measures such as monthly temperature averages, precipitation, and days with below-freezing temperatures.

Researchers were able to separate out which of these variables were most important in influencing infectivity rates by running different combinations of them through robust computer models.

The primary result showed that climate was the most influential factor in the model. Disturbance to natural habitats also had a major role in our findings, some of which ran counter to those of previous research. A model was developed using data obtained between 2009 and 2018, and then it was put to the test to determine how well it would do at predicting the occurrence and distribution of data collected in 2019.

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In his words, “we found it to be quite accurate,” Tran explains the results. “What’s even better is that a lot of the data we used to develop the model is free,” the authors write; “this means that other locales might be able to reproduce our findings to assist estimate Lyme disease risk, particularly in areas with a climate and geography similar to New York.”

Tran suggests public health message urging park visitors to check for ticks as an intervention to reduce the spread of disease. The results may also be used to inform future land management, with the hope of reducing Lyme disease risks through ecological means.

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