Immunological relationships of Long Island isolates of Babesia microti.

Studies to detect strain differences among two rodent-derived and one human-derived Babesia microti isolates from Long Island were undertaken, using various methods. Superinfection experiments using the homologous and heterologous isolates showed cross-protection. All hamsters were resistant to superinfection challenges of increasing dosages of both the homologous and heterologous isolates. Attempts to infect other laboratory animals with the Long Island isolates of B. microti were successful in intact and splenectomized Sprague-Dawley rats and questionable in Swiss mice. Nylar and CFW mice as well as CFW and Wistar intact and splenectomized rats were refractory to B. microti isolates from Long Island. Indirect fluorescence tests using convalescent sera from six Long Island cases of babesiosis showed no titer differences with tests using the three Long Island antigens as well as the Gray strain antigens. The rise of hamster IgG anti-B. microti antibody was followed by indirect immunofluorescence done at different parasitemia levels. The IgG antibody in hamsters was detected early in the course of infection, rose rapidly concurrent with increasing parasitemia, and became stable at high titers for the duration of the infection. IgG antibody titers were unaffected by homologous superinfection challenges.