A FATAL CASE OF BABESIOSIS IN MISSOURI - IDENTIFICATION OF ANOTHER PIROPLASM THAT INFECTS HUMANS

Objective: To characterize the etiologic agent (MO1) of the first repo rted case of babesiosis acquired in Missouri. Design: Case report, ser ologic testing, animal inoculations, and molecular studies. Setting: S outheastern Missouri. Patient: A 73-year-old man who had had a splenec tomy and had a fatal case of babesiosis. Measurements: Serum specimens from the patient were assayed by indirect immunofluorescent antibody testing and immunoprecipitation for reactivity with antigens from vari ous Babesia species. Whole blood obtained from the patient before trea tment was inoculated into hamsters and jirds and into calves and bigho rn sheep that had had splenectomy and were immunosuppressed with dexam ethasone. Piroplasm-specific nuclear small-subunit ribosomal DNA was r ecovered from the patient's blood by using broad-range amplification w ith the polymerase chain reaction; a 144 base-pair region of the ampli fication product was sequenced; and phylogenetic analysis was done to compare MO1 with various Babesia species. Results: Indirect immunofluo rescent antibody testing showed that the patient's serum had strong re activity with Babesia divergens, which causes babesiosis in cattle and humans in Europe, but that it had minimal reactivity with B. microti and WA1, which are the piroplasms previously known to cause zoonotic b abesiosis in the United States. Immunoprecipitations showed that MO1 i s more closely related to B. divergens than to B. canis (a canine para site). None of the experimentally inoculated animals became demonstrab ly parasitemic. Phylogenetic analyses, after DNA sequencing, showed th at MO1 is most closely related to B. divergens (100% similarity). Conc lusions: Although MO1 is probably distinct from B. divergens, the two share morphologic, antigenic, and genetic characteristics; MO1 probabl y represents a Babesia species not previously recognized to have infec ted humans. Medical personnel should be aware that patients in the Uni ted States can have life-threatening babesiosis even though they are s eronegative to B. microti and WA1 antigen.