Lyme disease study looks at factors that may increase threat
Lyme disease cases in Dutchess and Ulster counties are being underestimated in federal statistics. Alex H. Wagner/Poughkeepsie Journal
A new study examining nearly 20 years of data on forests and climate in Dutchess County may shed light on how ecology directly impacts the spread of Lyme disease.
Researchers at the Cary Institute of Ecosystem Studies, a not-for-profit environmental research and education organization based in Millbrook, analyzed the data and found a higher risk of contracting Lyme disease in forests with a larger rodent population and lower numbers of foxes, possums and raccoons.
They also found that tick-borne diseases, including Lyme disease, are closely tied with fluctuating acorn supply and predator communities in forests with many oak trees.
A research team spent 19 years collecting data and monitoring small mammals including mice and chipmunks, as well as black-legged ticks, climate and forests in Dutchess County. Richard Ostfeld, a disease ecologist at the Cary Institute, led the team.
Ostfeld said he hopes the information will help communities and residents determine how to exercise caution when they are outside, whether in their backyards or out in nature.
“Using nearly two decades of data on the forest food web, we were interested in untangling the ecological conditions that regulate the number of infected ticks in the landscape,” said Ostfeld.
The findings were recently published in an issue of Ecology, a journal of the Ecological Society of America.
Key findings included:
- Tick-borne diseases are linked with fluctuating acorn supply and the structure of the predator community.
- Forests with coyotes that lack a mix of bobcats, foxes and possums saw the highest risk of tick-borne diseases.
- Sites with high diversity in predators had lower infection in nymphal ticks – black legged ticks that are the size of a poppy seed – compared to sites dominated by coyotes. Coyotes sometimes displace other predators such as foxes and bobcats that are more effective at controlling rodent populations versus coyotes.
- The number of infected nymphal ticks was lowest at sites with denser forests and a greater diversity of predators.
- Climate impacts Lyme disease since humidity and moisture cause a greater number of infected ticks. Warm, dry spring or winter weather causes a decrease in infected ticks.
Ground zero for Lyme disease
The mid-Hudson Valley has been the epicenter of Lyme disease and 12,000-plus people in Dutchess County alone have been infected by the disease from 2000 to 2016. Counties in the Hudson Valley have a high number of black-legged ticks, which can carry Lyme bacteria.
According to the state Health Department's most recent report, Dutchess County saw 386 cases of Lyme disease in 2016 out of 7,543 cases in the entire state. Nearby Sullivan, Orange and Columbia counties also saw a high numbers.
Lyme disease is the fastest-growing vector disease in the U.S. with 30,000 new cases confirmed and reported annually to the Centers for Disease Control and Prevention. The number does not reflect every case of Lyme disease that is diagnosed in the U.S. each year.
Studying the data
The research is based off analysis from 19 years of data collected in Dutchess County. Since the early 1990s Ostfeld and a team of Cary’s researchers also monitored six forested field plots at Cary Institute’s grounds in Millbrook with a focus on small mammals, black-legged ticks, tick-borne pathogens, deer, acorns and climate. Up to 90 percent of the captures were mice and chipmunks.
In 2012 and 2013, researchers also monitored tick infection rates and predator communities at 126 sites throughout the county using black-LED camera wraps that were set throughout the county.
Over the years, some 50 scientists and researchers were involved – or continue to be involved - in the study.
“If it was warm and wet ticks did fine, but if it was warm and dry ticks didn’t do as well,” Ostfeld said. “Ticks spend some 95 percent of their time away from hosts, on the ground. They are sensitive to drying out and need moisture to survive.”
He called similarities - the effects of Lyme disease and the two other tick-borne diseases of anaplasmosis and babesiosis - “pretty cool.
“What is a good warning sign for one is also a good warning sign for the others,” he said.
Survivors look for solutions
Pat Smalley is a Town of Clinton resident and a Lyme disease survivor.
"We learn something from it the habitat that we need and we don’t need and what works and doesn’t work," Smalley said. "They're (Cary Institute researchers) trying different ways of controlling how to control the ticks. If we can get control of the ticks we can get a better control of the disease."
Those who suffer from Lyme disease say the research supports prevention and education.
"I believe their research leads to not only a better understanding, but a way that people can protect themselves in their own yards so when they go out they don’t go out and pick infected ticks in their yards and become sick," said Jill Auerbach, who suffers from Lyme disease and is chairwoman of the Hudson Valley Lyme Disease Association.
Auerbach, who said she is familiar with Ostfeld's research - including the most recent research study - takes care in discarding leaf litter and keeping her yard as sunny as possible since ticks do poorly in warm and dry weather. She also makes sure that the grass is regularly cut, and that the yard doesn't have any stones or logs since they tend to attract small rodents.
The 63-year-old scientist said he’s always been “inherently fascinated with the connection between ecology and the medical sciences.” But the topic also hit home for Ostfeld. When his two sons were little, they were stricken with tick-borne diseases, one with Lyme disease and the other Anaplasmosis.
“That was years ago, but it struck me that this is a personal issue. I’ve had neighbors, close friends and other family members get extremely ill from tick-borne diseases, not just Lyme disease but others,” he said. “I observe their sense of helplessness and need to get proper medical attention. That has helped ignite my need to help with prevention.”
And without vaccines giving people the right amount of information at the right time and place is important to reducing the cases of tick-borne disease, he said.
“If we are able to tailor the message to the years and places where we expect risks to be particularly high then maybe people would be more active in protecting themselves,” he said.
LYME ADVOCATE: Lyme disease: A mother’s journey as an accidental advocate
Amy Wu: email@example.com, 845-451-4529, Twitter @wu_PoJo
Lyme disease by the Numbers
30,000: Number of new Lyme disease cases reported each year to the Centers for Disease Control and Prevention.
300: Strains of Lyme worldwide
100: Strains of Lyme in the U.S.
50: Percentage of times a tick or bullseye rash is found
35-50: Percentage of times common blood testing shows a false negative
1: Lyme is the fastest-growing vector-borne disease in the U.S.
Source: The International Lyme and Associated Diseases Society and the Centers for Disease Control and Prevention