Babesiosis Tick Disease Spreads to Mid-Atlantic

Babesiosis, a tick-borne disease that affects red blood cells and can cause flu-like symptoms or more severe complications, has historically been confined to the northeastern United States. However, a new study shows it is quietly spreading southward into the mid-Atlantic region, raising new health concerns. Between 2009 and 2024, locally acquired human cases of babesiosis were documented for the first time in Maryland, Washington D.C., Virginia, and West Virginia. The parasite behind the disease—Babesia microti—is primarily spread by the blacklegged tick (Ixodes scapularis), the same species known to transmit Lyme disease and anaplasmosis, another disease with flu-like symptoms.

Researchers collected over 1,300 blacklegged ticks from forests, open fields, and animals in Delaware, Maryland, and Virginia. They found that 2.7% carried B. microti, though some sites showed infection rates as high as 12.5%. Even more concerning, half of the B. microti-positive ticks were also infected with Lyme disease, and one carried all three pathogens raising the risk of coinfection from a single tick bite.

The study also examined a lesser-known tick species, Ixodes keiransi, found in Delaware and Virginia. Though these ticks rarely bite humans, they tested positive for B. microti and Lyme disease in Virginia and for Lyme disease in Delaware. This is the first time these pathogens have been found in this species of tick from these states. The role of this species in disease spread is still being studied, but its overlap with blacklegged ticks may contribute to maintaining infection cycles in wildlife.