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Lyme study finds more tick infection in places with less human population

May 28, 2019

Connecticut researchers have found a direct link between the percentage of ticks infected with disease-causing bacteria and the incidence of Lyme disease among humans in the state.

More surprisingly, the state also found that the counties whose residents submit the most ticks to the state for testing — namely New Haven and Fairfield — aren’t the ones with the highest rates of infected ticks or Lyme disease.

In a recently published study in the journal Ticks and Tick-Borne Diseases, a team of researchers at the New Haven-based Connecticut Agricultural Experiment Station found a strong relationship between the prevalence of Borrelia burgdorferi, the bacteria that causes Lyme disease, in nymphal (or young) ticks submitted by state residents for testing, and the subsequent incidence of Lyme disease in humans across the state.

The findings were based on analysis of more than 30,000 blacklegged tick (also known as deer tick) submissions by state residents to the Agricultural Experiment Station’s Tick Testing Laboratory between 2007 and 2017.

The study “really does underscore the value of the state-supported tick-testing program,” said Dr. Theodore Andreadis, director of the agricultural experiment station. “When we see a high infection rate in the ticks brought in to us, it really a good reference for what’s going on out there.”

Researchers also found that the prevalence of tick infection was greater among ticks submitted from the state’s less populous counties — Windham, Tolland and New London — than those coming from the more populous New Haven and Fairfield counties.

“The prevalence of infection is high in these areas from which we aren’t receiving a lot of ticks,” said Dr. Goudarz Molaei, a research scientist and senior author on the paper who also directs the CAES Tick Testing Program.

He said the bulk of ticks the state receives for testing come from Fairfield and New Haven counties, which have both lower rates of infected ticks and Lyme disease in humans than Windham, Tolland and New London counties.

So far this season, 1,700 to 1,800 ticks have been submitted for testing, and about 40 percent of those tested were found to be infected with Lyme disease or another tick-borne illness.

Molaei said the research also confirmed the role of young, or nymphal, ticks in spreading Lyme disease, even though infection rates among adults are higher. The research showed that annual infection rates in nymphal ticks ranged from 15 to 41 percent with a 20-year average of 21 percent, while infection rates in adult ticks ranged from 27 to 39 percent with annul mean of 33 percent.

Despite the higher infection rates in adults, nymphal ticks are a concern because their small size makes them harder to detect, and the nymphs attach and feed quickly.

“Nymphs are playing an important role in making people sick,” Molaei said.

According to the Centers for Disease Control and Prevention, Lyme disease is the most commonly reported tick-borne disease in the United States. It affects about 329,000 people annually. The illness can cause severe damage to joints and the nervous system.

In 2017, Connecticut had the eighth highest incident rate of Lyme disease per 100,000 residents of all the states, and Connecticut also is one of the 14 states from which nearly 95 percent of Lyme disease cases in the United States are reported.

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