35-year monitoring study clarifies ecological forces behind Lyme disease risk
Tick-borne diseases are on the rise in the United States. Lyme disease is the most commonly reported, with nearly half a million people diagnosed each year. Caused by the bacterium Borrelia burgdorferi, it is most often spread by bites from blacklegged ticks. Lyme can be treated with antibiotics, but if untreated, infection can spread to the joints, heart and nervous system, and some people can…
A 35-year monitoring study at the Cary Institute of Ecosystem Studies in Millbrook, New York, has provided new insights into the ecological factors influencing Lyme disease risk. The research, published in Proceedings of the National Academy of Sciences, sheds light on how interactions between acorns, rodents, ticks, predators, and climate shape Lyme disease risk in people.
Lead author Richard Ostfeld, a disease ecologist, emphasized that these findings enhance our understanding of tick-borne disease risk and inform management strategies.
One key finding is that mouse abundance, rather than deer abundance, is strongly linked to higher numbers of nymphal ticks, the stage most likely to infect humans. A strong mouse year boosts the next year's number of nymphs by about 40%. This relationship is due to white-footed mice being a high-quality food source for blacklegged tick larvae and passing the Borrelia burgdorferi bacteria to the ticks as larvae.
The study also revealed that acorn masting—when oak trees produce a large number of acorns simultaneously—creates a food bonanza for mice, leading to increased populations and subsequent increases in nymphal tick numbers two years later. However, the researchers had initially expected that high mouse populations would also result in a higher prevalence of infected nymphs, but this relationship disappeared over time.
This discrepancy was explained by the fact that other hosts, such as skunks, squirrels, and opossums, were more prevalent in some years and were less effective at transmitting the bacteria to ticks.
Additionally, the research found that extreme heat and cold events do not substantially reduce tick populations in natural environments. Instead, ticks seem to survive better by sheltering deeper in soil and leaf litter. However, a trend was observed: years with warmer overall temperatures predict lower-than-normal numbers of nymphal ticks. This combination of factors—mouse abundance, host diversity, and temperature—will be crucial for public health officials to anticipate and manage periods of elevated Lyme disease risk.
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