Babesiosis
Babesiosis is a potentially severe, and sometimes rapidly fatal, tick-borne illness caused by a protozoan parasite that infects and destroys the red blood cells.
Babesia microti appears to be responsible for the majority of cases of human babesiosis in the United States. It is the most common species in the eastern and Midwestern U. S. where most cases occur. Additional types of
Babesia that have been associated with human disease in limited areas of the U.S., but that have not yet been designated as distinct species, are currently known only as
Babesia isolate type WA1 parasites (detected on the West Coast) and
Babesia isolate type MO1 (detected in Missouri).
Babesia species cause illness in animals. Babesia divergens is the most common species in Europe. Other Babesia species cause illness in animals.
How does a person get babesiosis?
You can get babesiosis if you are bitten by a tick that is infected with B. microti, or less commonly, another Babesia species. Protozoa in the tick's saliva are transmitted to you while the tick is feeding. An infected tick must be attached to you for at least several hours (usually 24-48) in order for transmission to take place. Occasionally, cases of babesiosis have also been acquired via blood transfusion from apparently healthy (asymptomatic, lacking symptoms), but nevertheless infected, individuals.
Do all ticks transmit babesiosis?
No. Only certain species of ticks are capable of transmitting Babesia. There are two vectors (transmitters) of
Babesia to humans in the United States. Ixodes scapularis, the blacklegged tick (also known as the “deer tick"), is the primary vector for
Babesia in the east and Midwest, while
Ixodes pacificus, the western blacklegged tick, is a presumptive vector along the West Coast.
Ixodes ricinus, sometimes referred to as the sheep tick or European castor bean tick, transmits
B. divergens in Europe. Simultaneous infections with both
B. microti andBorrelia burgdorferi, the agent of Lyme disease, have been documented in ticks, and there is evidencee that both organisms may be transmitted during a single tick bite.
How do ticks acquire Babesia?
Ticks become infected by feeding on an infected animal known as a reservoir host. Reservoir hosts carry
Babesia parasites in their bloodstream for a prolonged period of time, thus causing ticks that feed on them to become infected. Then, when the infected tick feeds on its next host, parasites are passed on to that host and the cycle of infection continues. Rodents, especially the white-footed mouse (Peromyscus leucopus), are the reservoir hosts for
B. microti, while in Europe, cattle serve as the reservoir hosts forB. divergens.
How prevalent is babesiosis?
Within the United States, human babesiosis does not appear to be geographically widespread. It is difficult to assess the true prevalence of the disease because it has not been designated as a nationally reportable illness to the Centers for Disease Control and Prevention (CDC). Also, it is suspected that many cases go undiagnoosed because of the lack of symptoms in many individuals. Since the first cases were recognized in California in 1966 (unknown Babesia species) and Massachusetts (Nantucket) in 1969
(Babesia microti), several hundred cases have been documented. The majority of these cases have occurred in southern New England, especially on the coastal islands of Massachusetts (Nantucket, Martha's Vineyard), Rhode Island (Block Island), and New York (Shelter Island, Long Island). Cases have also been reported in California, Connecticut, Missouri, New Jersey, Washington, and Wisconsin.
What are the symptoms of babesiosis?
Based on serologic (blood) studies, most infections appear to be asymptomatic. Manifestations of symptomatic disease include fever, headache, chills, sweating, musscle aches (myalgias), fatigue, nausea, vomiting, enlarged spleen and liver (sometimes resulting in jaundice), and hemolytic anemia (anemia due to the destruction of red blood cells). Symptoms usually occur 1 to 4 weeks following an infective tick bite, and can last for several days, weeks, or months. The disease is more severe, and sometimes fatal, in patients who are immunosuppressed (have aweakened immune system), lack a healthy spleen, or who are elderly. In some cases, parasites may continue to circulate in the blood of asymptomatic individuals for several months or even years, making transmission of babesiosis by blood transfusion a concern. Because there have been documented cases of transfusion-acquired babesiosis, the American Red Cross does not accept blood donations from anyone who has ever had babesiosis, even if they havee been treated with appropriate antibiotics. Co-infection with Lyme disease has been documented in some patients. Co-infection may complicate diagnosis and treatment, and may result in more severe illness in the individual.
How is babesiosis diagnosed?
Most patients do not remember a tick bite. Diagnosis is usually made by examining blood smears under a microscope and detecting Babesia within the red blood cells. Babesia appear as tetrad (cross-shaped) or ring-shaped forms, but may be very difficult to distinguish from the Plasmodium parasites that cause malaria. Therefore, a combination of diagnostic criteria may be useful. An indirect immunofluorescent antibody assay (IFA) test can be used to detect Babesia-specific antibodies in the blood. Serologic diagnosis is established by a four-fold orgreater rise in the serum titer betweeen the acute (early) phase and the convalescent (late) stage. In addition, patient blood can be inoculated into hamsters to observe resultant infection in these animals after 2 to 4 weeks. In some cases, polymerase chain reaction (PCR) may also be used to detect Babesia DNA in the blood. Because some patients may be co-infected with Lyme disease (10-25%), blood tests should also be performed for this infection. It is important to diagnose and treat both infections.
What is the treatment for babesiosis?
There are no standardized treatments for babesiosis. However, the following drug regimens have been found to be useful: quinine (650 mg 3 times/day)
plus clindamycin (600 mg 3 times/day or 1.2 g intravenously 2 times/ day) for 7-10 days (the dosages for children are quinine 25mg/kg
plus clindamycin 20-40 mg/kg, both given in 3 divided oral doses for 7 days),
OR azithromycin (600 mg 1 time/day)
plus atovaquone (750 mg 2 times/day) for 7-10 days (the dosages for children are azithromycin 12 mg/kg 1 time/day
plus atovaquone 20 mg/kg 2 times/day, for 7-10 days). Although all of these drugs are approved, the U.S. Food and Drug Administration currently considers clindamycin, azithromycin, and atovaquone investigational for babesiosis. Patients who exhibit only mild symptoms may require no specific therapy. Severely ill patients with a high percentage of infected red blood cells, on the other hand, may benefit from exchange transfusion (removal of the patient's infected blood, followed by replacement with clean, donated blood). Dialysis may be required for patients with kidney failure.
What can I do to reduce my risk of becoming infected with babesiosis?
There is no vaccine against babesiosis. Therefore, you can help prevent babesiosis, and other tick-borne diseases, by protecting yourself from ticks. When in tick habitat (tall grass and weeds, scrubby areas, woods and leaf litter), utilize the DOD Insect Repellent System.
Select the image for more information on the DoD Insect Repellent System.
