Babesiosis is an emerging zoonotic tickborne parasitic disease in the United States and occurs primarily in the Northeast and Midwest.
According to a recent Morbidity and Mortality Weekly Report (MMWR) from the Centers for Disease Control and Prevention (CDC), Babesiosis trends were assessed in 10 states where babesiosis was reportable during 2011–2019.
Incidence increased significantly in Connecticut, Maine, Massachusetts, New Hampshire, New Jersey, New York, Rhode Island, and Vermont, with the largest increases reported in Vermont (1,602%, from two to 34 cases), Maine (1,422%, from nine to 138), New Hampshire (372%, from 13 to 78), and Connecticut (338%, from 74 to 328).
Unlike the other seven states, Maine, New Hampshire, and Vermont, were not included as states with endemic disease in previous CDC babesiosis surveillance summaries. These three states should now be considered to have endemic transmission comparable to that in other high-incidence states; they have consistently identified newly acquired cases every year during 2011–2019 and documented presence of Babesia microti in the associated tick vector. Because incidence in Northeastern states, including Maine, New Hampshire, and Vermont, is increasing, tick prevention messaging, provider education, and awareness of infection risk among travelers to these states should be emphasized.
The first case of human babesiosis acquired in the United States was identified in 1969 on Nantucket Island, Massachusetts. In 2011, babesiosis became a nationally notifiable condition.
During 2011–2019, a total of 16,456 cases of babesiosis were reported to CDC by 37 states, including 16,174 (98.2%) reported from the 10 states included in this analysis–Connecticut, Maine, Massachusetts, Minnesota, New Hampshire, New Jersey, New York, Rhode Island, Vermont, and Wisconsin.
New York reported the largest number of cases (4,738 total; average = 526.4 per year), followed by Massachusetts (4,136; 459.6), and Connecticut (2,200; 244.4).
Because case counts and rates have increased, clinicians need to be aware of the signs and symptoms of and risk factors for babesiosis in their practice areas, particularly as other tickborne conditions can have similar clinical manifestations, risk for disease acquisition, and geographic distribution.
Lastly, the expansion of babesiosis risk could have implications for the blood supply. Babesia is transmissible via blood transfusion, and persons who acquire babesiosis through contaminated blood have been shown to have significantly worse health outcomes and a higher risk for death than do those who acquire the disease from a tick bite. Currently, the FDA recommends blood donation screening for babesiosis in 14 states and the District of Columbia. Babesiosis risk in Maine, New Hampshire, and Vermont is comparable to that in the northeastern and midwestern states where babesiosis has been considered endemic, and FDA guidance recommends blood donor screening for Babesia infection in those states. Ongoing evaluation of both tickborne and transfusion transmission risks in states that border those with endemic transmission is important for the evaluation and evolution of babesiosis blood screening policy.