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November 12, 2021

A new article led by the USGS summarizes what’s happening in Rhode Island, specifically what diseases transmitted by ticks are present, which tick species have recently spread into the region and the likely reasons for these shifts.

larval blacklegged ticks
 Larval blacklegged ticks host-seeking on leaf litter. Photograph Credit: Graham Hickling, University of Tennessee

Cases of tick-borne diseases in humans, particularly Lyme disease, have been increasing for decades in the United States. Rhode Island is one of many northern states experiencing increases in tick-borne diseases. According to the Centers for Disease Control and Prevention, there are thousands of cases annually in the state.

The major tick of concern in Rhode Island is the blacklegged tick, also called the deer tick. It transmits the pathogens that can cause diseases such as Lyme, babesiosis and anaplasmosis, all of which have rising cases and are expected to continue to increase.

In previous research, the USGS and partners found a few significant factors that contribute to the higher infection rates from blacklegged ticks in the north. Northern blacklegged ticks abundantly seek food sources, known as hosts, on top of the leaf litter and twigs where they can frequently encounter people. Research suggests that

the climate may play a part in this pattern, as warmer temperatures in the south may cause ticks to stay below the leaf litter surface.

Research has also found that black-legged ticks in the north attach to and feed off mammals, such as rodents and shrews, that are efficient at carrying and spreading the bacteria that cause these diseases.

Two other human-biting tick species are present in Rhode Island, and they are the lone star tick and American dog tick. Lone star ticks were formerly southern in distribution and have recently spread northward, including expansion into Rhode Island. The American dog tick is present widely in the eastern U.S., and warmer temperatures may result in larger populations in the northern U.S. and Canada.

Nymphal blacklegged tick host-seeking on leaf litter. Photograph Credit: Graham Hickling, University of Tennessee

The American dog tick can transmit bacteria that cause diseases such as Rocky Mountain Spotted Fever. The lone star tick can transmit bacteria that cause diseases such as ehrlichiosis. Also, the bite of the lone star tick can cause alpha-gal syndrome, which is an allergy to red meat and other products made from mammals. These diseases are far less common than some of those transmitted by the black-legged tick, but both species present potential implications for human health.

More research is needed to better understand the reasons for changes in tick distributions and disease occurrence, and what might happen in the future. There are several likely contributing factors, including climate change and alterations in land use practices that can modify where suitable habitats are available for ticks and the animals ticks attach to for feeding.
 
Rhode Island is likely to remain in the main region experiencing Lyme and other major tick-borne diseases in the foreseeable future. Science by the USGS and partners is helping people understand and predict the spread of these diseases and determine where human health threats could occur, ultimately informing management decisions to protect communities.

 Read the article in the Rhode Island Medical Journal at http://rimed.org/rimedicaljournal/2021/11/2021-11-29-climate-ginsberg.p….

To learn more about how to prevent tick bites and check for symptoms of related diseases, visit the Centers for Disease Control and Prevention’s website at https://www.cdc.gov/ticks.