Geographical distribution of leptospira-positive field rodents in Japan.

Many papers have been published on leptospira-positive rodents in selected areas of Japan. Rattus norvegicus, R. rattus, and R. rattus alexandrius trapped in urban areas and certain swamp rice fields in rural areas were found to carry L. icterohaemor-The latter two species of rodents are caught generally in the field and forest in rural areas. data), have been isolated from the rodent in Japan. With field rodents and other animals trapped in a country-wide survey on rickettsia-positive animals (Tamiya , 1962), attempts have been made to know what species of animals are leptospira positive and to elucidate geographical distribution of such animals in Japan excluding the Okinawa Islands. Of all animals trapped in 428 areas in Japan during the period 1955-1962 , 4,108 were used in this investigation. The animals were identified finally by Dr. Y. Imai-zumi, the National Science Museum (Natural History Institute) , Tokyo. They were comprised of 35 species and their geographical distribution is given in Table I and was illustrated in more details in a book (Tamiya , 1962). The kidneys to be tested were fixed in 5 % formalin and stained by Levaditi method. The section of the stained kidney was examined under a microscope; leptospires were morphologically confirmed in the lumen of the convoluted tubules of the kidney (Fig. 1). Figure 2 indicates geographical distribution of leptospira-positive and-negative animals in 428 areas in 38 prefectures from Wakkanai, the northernmost town in Hokkaido, to Amami Oshima Island, the southernmost island in Kagoshima prefecture. In some areas repeated surveys were performed in different seasons , but generally a single survey of an area was conducted during a certain season. Our former surveys (Kitaoka et al., 1935; Kitaoka and Ogawa, 1942) on leptospira-positive field rodents revealed that the heavier the body weights of rodents , the higher the leptospira-positive rate in the kidneys. Accordingly, negative areas on the map do not strictly mean no-epidemicity in leptospira-positive small animals. One hundred and twenty-five of 428 areas surveyed were found to be leptospira-positive. These areas included Shiretoko Peninsula, Hokkaido in the north, and Amami Oshima Island , Kagoshima prefecture in the south. Table II indicates the species of field rodents and other small animals trapped for leptospira surveillance in eight districts in Japan. One hundred and forty-six of 277 278 KITAOKA et ISHIMARU Vol. 27 TABLE I Leptospira-positive rates of small animals trapped in Japan, 1955-1962 279 1974 NOTES …