Apicomplexan parasites of the genus Babesia cause
babesiosis in humans and animals worldwide.
Human babesiosis is a predominantly
zoonotic disease transmitted by hard ticks that is of increasing health concern in the USA and many other countries. Microscopic examination of stained blood smears, detection of serum
antibodies by immunoassays and identification of parasite
nucleic acid in blood by qPCR and fluorescence in situ hybridization (FISH) are some methods available for diagnosing
babesiosis. This study investigated the use of a Babesia genus-specific FISH test for detecting Babesia parasites in blood smears and immunofluorescence assay (IFA) for detecting serum
antibodies to Babesia duncani and Babesia microti, two common species that cause
human babesiosis in the USA. The findings with clinical samples originating from USA, Australia, Europe and elsewhere demonstrate that the parallel use of Babesia genus-specific FISH and IFA tests for B. duncani and B. microti provides more useful diagnostic information in
babesiosis and that B. duncani
infections are more widespread globally than presently recognized.