A new report in Open Forum Infectious Diseases details the significant increase of the Babesia season in New England since the 1980s, and the authors said warming trends in the region may lead to accelerating tick life cycles and increasing tick activity outside of the traditional summer months.
Babesiosis is parasitic disease primarily spread by blacklegged (deer) ticks, which infects red blood cells. While some have no symptoms, many people will experience flu-like symptoms and in severe cases, the disease can lead to hemolytic anemia if not treated.
To measure incidence over time, the authors conducted a chart-review of cases seen at three Boston hospitals between May 1, 1993, and May 1, 2024. Of the 1,130 cases included in the study, 986 were probably acquired in Massachusetts, 43 in New Hampshire, 25 in Rhode Island, 8 in Maine, 6 in Connecticut, and 1 in Vermont.
Biggest increases in Maine, Vermont
According to the authors, between 2011 and 2019, the incidence of babesiosis increased by 193% in Massachusetts, 338% in Connecticut, 1,422% in Maine, and 1,602% in Vermont.
Babesia diagnoses showed a strong correlation with each unit increase in time (year), resulting in an annual growth in cases of 14.2% (95% confidence interval [CI], 13.1% to 15.2%).
“We observed a significant expansion of the babesiosis season in the past 31 years with the mean number of months per year with cases rising from 2.2 before 2000 to 9.2 after 2015,” the authors concluded.