Borne by Deer Ticks, Babesiosis Is Spreading in the Northeastern United States

Kenny Lin, MD, MPH
Posted on March 20, 2023

The Centers for Disease Control and Prevention reported last week that the incidence of babesiosis rose substantially in 10 northeastern states from 2011 to 2019, including Maine, New Hampshire, and Vermont, where it was not previously considered to be endemic. Maps from a previous American Family Physician article on tickborne diseases illustrate the geographic distribution of babesiosis compared with other tickborne diseases such as Lyme disease. Babesiosis is usually transmitted to humans by the bite of an infected deer tick (Ixodes scapularis), although rare cases of transfusion-associated and perinatal transmission have been reported.

The Environmental Protection Agency has concluded that the expanding range of disease-carrying ticks to northern latitudes has been influenced by ongoing climate change:

Deer ticks are mostly active when temperatures are above 45˚F, and they thrive in areas with at least 85-percent humidity. Thus, warming temperatures associated with climate change are projected to increase the range of suitable tick habitat. … Because tick activity depends on temperatures being above a certain minimum, shorter winters could also extend the period when ticks are active each year. … Unlike some other vector-borne diseases, tick-borne disease patterns are generally less influenced by short-term changes in weather (weeks to months) than by longer-term climate change.

After an incubation period of one to nine weeks, patients with babesiosis can experience nonspecific flulike symptoms, including fever, generalized weakness, and myalgias. More severe complications may develop, including acute respiratory distress syndrome, congestive heart failure, and disseminated intravascular coagulation. The diagnosis can be made by polymerase chain reaction or microscopic identification of intraerythrocytic organisms on a Giemsa-stained peripheral blood smear.

First-line treatment for mild to moderate babesiosis is oral atovaquone and azithromycin for seven to 10 days. More severe infections should be treated with intravenous clindamycin and oral quinine. Exchange transfusions are “reserved for patients who are extremely ill – with blood parasitemia of more than 10 percent, massive hemolysis and asplenia.” Because coinfection with Lyme disease and ehrlichiosis can occur, clinicians can consider starting oral doxycycline while awaiting the results of serologic testing. Babesiosis may persist for more than two months after effective treatment and for months to years in patients with unrecognized infections.

A previous American Family Physician editorial provided advice on use of effective insect repellents to prevent diseases carried by ticks and mosquitoes. A patient education handout reviewed strategies for preventing tick bites and safely removing attached ticks. Finally, readers interested in mitigating infectious and other health impacts of warming temperatures in their clinics and communities can consult a curated collection of articles on environmental health and climate change.