Studies on babesia first found in murine in Japan: Epidemiology, morphology and experimental infection

During the period from November 1980 to September 1982, 314 small wild mammals were captured in 5 localities in Japan. Twenty-six out of 86 Apodemus speciosus and one out of 6 A. argenteus both species captured in Shiga Prefecture (35°02′N, 135°50′E, 330 m elev.) were positive for babesia. The parasitemia in those animals was generally low. The infection rate did not show any significant difference between sexes of the host or between seasons, whereas it tended to go up with the increase of the body weight of the host. Several developing stages were seen by light microscopic examination such as small to large sizes of ring forms, ameboid forms, dividing forms which finally formed 4 merozoites.

The susceptibility of several kinds of experimental and wild animals to this babesia was studied. It was the highest in the nude mouse followed by the golden hamster, mongolian gerbil, mouse and rat. Furthermore, Microtus montebelli, A. speciosus, Clethrionomys rufocanus, Japanese monkey (splenectomized) and crab-eating monkey (splenectomized) became positive for babesial infection after experimental inoculation. The intensities of infection in those animals were generally very low although the infection continued for as long as two months. The Japanese monkey, crab-eating monkey, dog, cat and Eotbenomys smithi (all without splenectomy), and Guinea pig and rabbit (both with and without splenectomy) were negative for babesia after being infected in the same manner.

This is the first report of murine babesia in Japan. Although this babesia is not different from Babesia microti as far as the present examination shows, we intend to give a specific name to this parasite when the experiment on vector is completed.