Anaplasmosis diagnoses in Maine reached a record high in 2019 with at least 685 confirmed cases of the tick-borne illness, while the number of Lyme disease cases also were up, rebounding following a decline in 2018.

“Ticks were abundant and highly active in 2019,” said Griffin Dill, integrated pest management specialist at the University of Maine Cooperative Extension. The university operates a “tick lab” and studies tick-borne illnesses.

Researchers studying the rise in tick-borne illnesses – anaplasmosis cases in Maine have climbed more than tenfold since 2012 – are looking at factors that include increased testing and climate change.

While both Lyme and anaplasmosis are transmitted by the deer tick and have the same symptoms – fever, joint pain, swelling, fatigue, headaches and neurological problems like Bell’s palsy – anaplasmosis is typically more severe. About 25 percent of anaplasmosis patients are hospitalized, compared to about 5 percent of Lyme patients. The diseases require similar treatment – a course of antibiotics for a bacterial infection.

There were 1,461 cases of Lyme disease in 2019, according to preliminary data from the Maine Center for Disease Control and Prevention. That’s a 7 percent increase over the 1,370 cases in 2018, but well below the record 1,852 reported in 2017.

Anaplasmosis showed the biggest increase in 2019, rising 44 percent from the 476 cases in 2018. The number of anaplasmosis cases peaked at 663 in 2017 and has risen dramatically since 2012, when there were 52 confirmed diagnoses.


The CDC also reported 138 cases of babesiosis in 2019, another tick-borne illness.

The final numbers for 2019 will be slightly higher for tick-borne diseases, as there’s a lag in reporting some cases. For instance, if a patient tested positive for Lyme in November, but the patient’s doctor did not report the case to the Maine CDC until January 2020, that case would be added to the 2019 report.

Dill said researchers still are gathering information about 2019, and there are many unknowns about why anaplasmosis cases surged. Of the ticks that were submitted to the Maine tick lab in 2019, 8 percent tested positive for anaplasmosis, compared to 38 percent of ticks that tested positive for Lyme, Dill said.

“It might be that there’s hot spots in certain geographical areas for ticks infected with anaplasmosis, and that those ticks may be more likely to be in areas with more human activity,” he said.

Also, Dill said doctors may be more likely to order tests for anaplasmosis now compared to five years ago, so cases that were not diagnosed years ago are more likely to be reported now. Maine is following a pattern seen in other states where Lyme disease becomes rampant, followed a few years later by increased prevalence of anaplasmosis and babesiosis.

Meanwhile, researchers are studying how climate change is affecting tick range and habitat, and how seasonal weather patterns may play a role. For instance, the hot and dry summer of 2018 may have contributed to reduced Lyme disease cases, while Maine experienced a wetter and more humid summer in 2019, Dill said. Ticks thrive in damp and humid conditions.


Dill said an early November snow in 2018 may have reduced tick activity, while there wasn’t as much snow through late fall of 2019.

“The ticks are unlikely to crawl through several inches of snow,” Dill said. “They are more likely to hide under the leaf litter under the snow, and wait until the snow melts before questing for a host.”

Dill said a new law passed by Congress, the TICK Act, co-sponsored by Sen. Susan Collins, R-Maine, will be a great help in the future for researchers to do more comprehensive field surveillance of ticks in Maine, and to improve diagnostics so that more people are tested for the disease. Dill expects some of the TICK Act funding to be distributed in Maine.

The TICK Act includes $100 million in federal spending, doled out in $20 million increments over the next five years. The U.S. Centers for Disease Control and Prevention would award grants to state health departments to “improve data collection and analysis, support early detection and diagnosis, improve treatment and raise awareness,” Collins’ office said in a December news release.

The prevalence of tick-borne diseases is much higher than the reported number, by about 10 times, according to the U.S. CDC, because of misdiagnoses or cases that are not diagnosed. Nationally, there were 42,743 reported cases of Lyme in 2017, the most recent year available, and 5,762 anaplasmosis cases.

Paula Jackson Jones,  president and co-founder of Maine’s Midcoast Lyme Disease Support and Education, who lobbied for the TICK Act, said it should provide better collaboration between the states.

“Hopefully, this will result in some really good answers, finding some really good solutions to this,” Jackson Jones said.


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