Diagnosis
Only specialized laboratories can adequately diagnose Babesia infection in humans, so Babesia infections are considered highly under-reported. It develops in patients who live in or travel to an endemic area or receive a contaminated blood transfusion within the preceding 9 weeks, so this aspect of the medical history is vital. Babesiosis may be suspected when a person with such an exposure history develops persistent fevers and hemolytic anemia. The definitive diagnostic test is the identification of parasites on a Giemsa-stained thin-film blood smear.So-called "Maltese cross formations" on the blood film are diagnostic (pathognomonic) of babesiosis, since they are not seen in malaria, the primary differential diagnosis. Careful examination of multiple smears may be necessary, since Babesia may infect less than 1% of circulating red blood cells, thus be easily overlooked.Serologic testing for antibodies against Babesia (both IgG and IgM) can detect low-level infection in cases with a high clinical suspicion, but negative blood film examinations. Serology is also useful for differentiating babesiosis from malaria in cases where people are at risk for both infections. Since detectable antibody responses require about a week after infection to develop, serologic testing may be falsely negative early in the disease course.A polymerase chain reaction (PCR) test has been developed for the detection of Babesia from the peripheral blood. PCR may be at least as sensitive and specific as blood-film examination in diagnosing babesiosis, though it is also significantly more expensive.
"Clinical Practice Guidelines by the Infectious Diseases Society of America (IDSA): 2020 Guideline on Diagnosis and Management of Babesiosis". Clinical Infectious Diseases. 72 (2): e49–e64. doi:10.1093/cid/ciaa1216. Homer MJ, Aguilar-Delfin I, Telford SR, Krause PJ, Persing DH (July 2000). "Babesiosis". Clin. Microbiol. Rev. 13 (3): 451–69. doi:10.1128/CMR.13.3.451-469.2000. PMC 88943. PMID 10885987. "Babesiosis: Overview"—The Merck Veterinary Manual
Current status of Equine piroplasmosis worldwide at OIE. WAHID Interface—OIE World Animal Health Information Database
Disease card—OIE