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.
As at the time of writing (2002), approximately 200 cases of babesiosis have been reported in the U.S. since the first human case was recognized on Nantucket Island (off the coast of Massachusetts) in 1968.
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.
The symptoms of babesiosis normally begin about a week after a tick bite with a gradual onset of malaise, anorexia and fatigue. This is followed several days later by high fever, chills, drenching sweats, muscle pain, joint pain and headaches. As with malaria, these symptoms can continue over a protracted period (several days to several months) or can abate, then recur. Sometimes, a person can be infected with the parasite but not show any symptoms. In some cases it may take from 1 to 12 months for first symptoms to appear after infection with the parasite.
There is no specific treatment for babesiosis. However, some medications used in the treatment of malaria have also been useful in the treatment of babesiosis.
While many in the U.S. who are exposed to the parasite do suffer severe symptoms, such cases often are self-limiting and are eventually resolved with treatment; fatalities generally are limited to elderly patients with compromised immune systems.
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.
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