Babesia Species is a topic covered in the Johns Hopkins ABX Guide.

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  • Malaria-like protozoan infection infects erythrocytes.
  • Greater than 100 species worldwide. Most human infections due to the rodent strain B. microti in the U.S. while B. divergens and B. bovis cattle strains cause human illness in Europe and elsewhere.
    • Phylum Apicomplexa
    • Four clades:
      • B. microti (account for most human infections in the U.S.)
      • B. duncani and B. ducani-like (dogs, wildlife, occasional cause of human infection Pacific NW)
      • B. divergens (primarily cattle pathogen)
      • B. venatorum (deer, largest case series described in China)
  • Transmitted by Ixodes (hard bodied) ticks, mostly occurs from May to September.
    • Common, global zoonosis (domestic and wild animals), may rarely infect humans.
    • In the U.S., mostly seen in Northeast and upper Midwestern states--most due to B. microti transmitted by I. scapularis (deer ticks).
    • Incubation period: 1-6 weeks
  • Most frequent pathogen transmitted by blood transfusion in the U.S.
    • May also be transmitted to the fetus during pregnancy.
  • Occasional infections documented by other species. The importance is that standard Babesia microti serology may not detect these infections.
    • B. duncani and B. duncani-like strains occurring in the Pacific Northwest.
    • B. divergens-like organisms: WA-1 described in California and Washington state. Strain MO-1 described in Missouri.
    • Europe: B. divergens > B. venatorum, B. microti.
      • Ixodes ricinus (sheep tick) is the primary vector.
    • Asia: B. microti-like organisms in Japan, Taiwan, S. Korea.

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Last updated: June 6, 2019