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Human Babesiosis

Human babesiosis is a malaria-like disease caused by a protozoan parasite that develops inside red blood cells of humans and small rodents. Several hundred human cases have been reported in the U.S., with the most serious infections occurring in the people with a weakened immune system.
Causative agent
  • A protozoan parasite with the scientific name Babesia microti.
Geographical distribution of cases
  • Most cases occur on islands off the coast of New England and Long Island, NY
  • Some cases are known from the central and western U.S.
Symptoms of infection
  • Typically asymptomatic or, at most, mild flu-like and self-limiting.
  • Can develop into a malaria-like disease, with fever, chills, sweating, headache, and muscle ache.
  • Additional symptoms include joint pain, nausea, vomiting, and prostration.
  • Repeating episodes of clinical disease can persist for months eventually leading to anemia, jaundice, and blood in urine.
Reservoir hosts of Babesia microti
  • The white-footed mouse, Peromyscus leucopus, and meadow voles.
Vectors of Babesia microti
  • Nymphs of Ixodes scapularis, the black-legged tick, in the eastern U.S.
Modes of transmission
  • From infected Ixodes scapularis nymphs to humans via their bite.
  • From infected Ixodes scapularis larvae to nymphs to adults via transstadial transmission.
  • NOTE: there is no human-to-human transmission, but infection via blood transfusion is documented.
Diagnosis of infection
  • Symptoms together with late summer-early fall onset.
Treatment of infection
  • Most cases are self-limiting; mild cases may require supportive measures.
  • Severe infections are treated by the physician-prescribed medicines quinine and clindamycin in combination.
Prevention of infection
  • There is no vaccine.
  • Avoid Ixodes scapularis habitat and contact with tick-infested vegetation ( see E-243-W "The Biology of Indiana Ticks").
  • Wear clothing consisting of a long sleeved shirt, long pants, and boots.
  • Use a repellent recommended by CDC and treat clothing with permethrin.
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