Babesiosis is a malaria-like illness caused by a protozoan, babesia microti, WA-1, MO-1, sometimes fatal in the elderly or those with no spleen. It may be more severe in patients with coexisting Lyme.  Symptoms include fever, chills, fatigue, headache, muscle pain, sweats and anemia. Treatment may be atovaquone with azithromycin or clindamycin and oral quinine.

Ticks that transmit babesiosis include Ixodes scapularis (deer tick) and Ixodes pacificus (western black legged) both of which also transmit Lyme disease.

Babesiosis has also been transmitted in humans through blood transfusions. 

Tests for babesiosis include IFA (Immunoflourescent Assay, IgG & IgM), FISH (Flourescent in-situ Hybridizition) and PCR (Polymerase Chain Reaction).