Lyme disease rates rise slightly

Fri, 12/22/2017 - 9:45am

“The proportion of people that showed evidence of recent or past infection with Lyme disease was one third of the people tested, which was a little higher than in previous years.”

That’s what Dr. Peter Krause said of results from the free Lyme disease testing at the Block Island Medical Center on Oct. 9. Krause, of the Yale School of Medicine and Public Health, and Dr. Maria Diuk-Wasser of Columbia University, conducted the testing. Krause has been conducting testing on Block Island for the past 25 years, while Diuk-Wasser has been performing field research for the past six years. 

Krause said that roughly 30 percent of the island population report tick bites each year, and that only 25 percent of the ticks on Block Island are infected. He noted that a tick must be attached for about 36 to 48 hours for someone to contract Lyme disease. 

“We tested 158 people,” said Krause, noting that 400 letters went out to island residents regarding the testing. “In total, 29 percent of the people tested positive for Lyme disease and one percent for babesiosis. This means they were exposed to the pathogens, but they didn’t necessarily develop disease symptoms.” (Krause said that 29 percent equals 46 cases on the island.)

Krause noted that “these values don’t necessarily represent the whole population of Block Island. People that took part in the (testing) may be most concerned about being positive because they have an increased risk of exposure to ticks, compared with people who do not attend (the study). If this is true, then the percentage of positive results would be lower if we were able to test all Block Island residents.”

Diuk-Wasser said that people who tested negative likely had “limited exposure to ticks, because they spent time indoors or less time in a tick-infested environment.”

Also, “not every tick is infected,” said Pilar Fernandez, a postdoctoral research fellow at Columbia University who is collaborating on the research. Fernandez said nymph deer ticks go undetected on human skin because they are so minute. She said the problem is that most people don’t see ticks until they’re engorged, or swollen; and by that time they could be infected.

As for what’s been learned from the testing, Diuk-Wasser said, “We know that tick-transmitted diseases like Lyme and babesiosis have been occurring on Block Island for many years, with an established transmission cycle that involve mice and deer as their main hosts. This round of testing, when put together with the results of previous years of testing, allow us to know the magnitude of the problem and track changes through the years to learn how transmission changes over time.”

“We test for antibodies to Lyme disease and babesiosis,” said Krause. “Antibodies decrease after infection and usually disappear after a year or two. People who tested negative may have had Lyme disease and/or babesiosis many years ago and yet still test negative.” 

“Every year the data is useful,” said Krause. “Our collaboration is important to help us understand what’s going on.”

“Combining the serosurvey data with the ecological data that we collect every summer on Block Island allows us to investigate what is happening in the natural disease cycle involving ticks, mice, and deer that may spill over into human populations,” noted Diuk-Wasser. “For example, we may be able to tie higher rates of bacteria in the tick populations for a given summer to higher rates of human infection. With this information, we can better design interventions that lower human risk of tick-transmitted diseases, while keeping the activities and lifestyle of the Block Island community in mind.”

Diuk-Wasser feels that her team needs “to better understand how people are exposed to ticks and become infected. Last summer we launched a smartphone app to address this gap in knowledge, which we are improving and expanding next summer.” 

“Lyme disease and other diseases transmitted by ticks continue to affect the Block Island community each year,” said Diuk-Wasser. “Therefore, this project is ongoing and is a priority for our research team. Next summer we will be launching a research study that will help us address the unanswered questions about what it is, on a daily basis, which puts community members at risk for diseases transmitted by ticks. We would like to reach out to Block Island residents and visitors to collaborate with us on this project. We’ll have more news during the spring of 2018.”

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