Babesiosis is a rare, serious, and sometimes fatal disease spread by the northern deer tick. Ticks can carry a parasite called Babesia microti that attacks the red blood cells of many animals, including man.
Babesiosis is a malaria-like illness caused by a protozoan parasite (Babesia microti in the U.S.; other members of the Babesia genus in Europe) that invades red blood cells, and is primarily transmitted by the deer tick Ixodes scapularis and possibly other related Ixodid ticks.
In the US, the deer (black-legged) tick in the Northeast and upper Midwest, and the Western black-legged tick on the Pacific coast are the primary carriers. A majority of reported cases occur during the summer months along the immediate coast and off-shore islands of the Northeast.
Babesiosis occurs most often in the elderly or in people who already have a problem with their immune system.
Babesiosis can, in extremely rare cases, be spread person-to person through blood transfusions.
In Europe, reported fatal cases of babesiosis have occurred mostly in patients whose spleens have been removed, rendering them more vulnerable to infection. The offending parasite in these cases have been either B. divergens or B. major, to which humans (with spleens intact) are thought to be naturally resistant. In the U.S., reported fatal cases have occurred in patients both with and without spleens; B. microti may be a more virulent agent to which humans are not naturally resistant.