Ticks Packing More than One Disease in Single Bite

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Some ticks are nearly twice as likely than previously expected to carry not only the Lyme disease bacterium but also the organism that causes babesiosis, according to findings from a new study published in the journal PLOS ONE.

Lyme disease is the most common tick-delivered illness. It can cause a rash in its early stages and, if not treated with antibiotics, can affect the central nervous system and heart.

Babesiosis is an infectious disease that, though treatable, can escalate to malaria-like symptoms of high fever, chills and anemia.

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For the study, researchers from Bard College, Sarah Lawrence College, and the Cary Institute of Ecosystem Studies examined thousands of blacklegged ticks from more than 100 sites across Duchess County, NY, an area known for its frequency of tick-borne sickness.

The researchers took DNA samples from each tick and documented the presence of several brands of pathogen. They found that nearly 30 percent of the ticks carried the bacterium for Lyme disease, and that about one third of those ticks also carried a second pathogen.

About 7 percent of the ticks contained both Lyme disease and babesiosis. The team crunched some probability numbers for this kind of co-infection occurring by chance alone vs. the data they observed and found the likelihood of co-infection was greater than expected.

Ticks typically get their pathogens from infected wildlife. Lead author of the study, and assistant professor of biology at Sarah Lawrence College, Michelle Hersh, singled out two such critters. "Mice and chipmunks are critical reservoirs for these two pathogens, so ticks that have fed on these animals are much more likely to be co-infected," she said.

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Just as spooky as the double-pathogen delivery was the team's finding that the chance of a triple infection -- Lyme, babesiosis and anaplasmosis (which causes anaplasmosis in humans) -- was twice as likely as expected.

The moral of the story? Expect the unexpected, if you get a tick bite.

"People in tick-infested parts of the United States such as the Northeast, Mid-Atlantic, and Upper Midwest, are vulnerable to being exposed to two or three diseases from a single tick bite," said the paper's co-author Felicia Keesing, a biology professor at Bard College and an Adjunct Scientist at the Cary Institute. "Health care providers and the public need to be particularly alert to the possibility of multiple infections."