Continuous in vivo culture and indirect fluorescent antibody test for zoonotic protozoa of Babesia microti.

Babesiosis has attracted attention as a zoonotic disease. The disease is caused in immunocompetent individuals almost solely by Babesia microti, a rodent babesia. Most cases of human babesiosis by B. microti have been reported in the endemic foci of the Northeastern coastal areas and upper Midwest regions of the United States, while some sporadic cases have recently been reported in several Asian countries including Japan. Our previous surveys identified that four small subunit ribosomal RNA gene (SSUrDNA) types of B. microti parasitize Japanese rodents. Indirect fluorescent antibody test (IFAT) is often performed for the diagnosis of babesiosis together with microscopical examination of thin blood smears and PCR. We established IFAT against four SSUrDNA-types of B. microti using erythrocytes of SCID mice or Syrian hamsters infected with each SSUrDNA-type B. microti. The results of IFAT for sera of ICR mice or Syrian hamsters infected with each SSUrDNA-type B. microti demonstrated that the four SSUrDNA-types of B. microti have different serotypes. Here, we report technical or practical procedures of IFAT, which gains sufficiently stable results, including procedures of continuous in vivo culture of B. microti.