The Lyme disease spirochete Borrelia burgdorferi was detected in the adult stage of the ixodid ticks Ixodes persulcatus and I. ovatus collected in various localities in Japan. The total prevalence values were 16.6% of 777 I. persulcatus and 23.6% of 687 I. ovatus. Sixty-two (63.9%) of 97 isolates from I. persulcatus contained the 30-34-kD heterogeneous outer surface protein A (OspA) that reacted with monoclonal antibody H5332. In contrast, all 128 isolates from I. ovatus were homogeneous with regard to the type of 30-kD OspA protein, and were different from the I. persulcatus isolates in their protein composition. These data suggest that the transmission cycle of B. burgdorferi in I. ovatus is not related to that in I. persulcatus. No cases of Lyme disease transmitted by I. ovatus have been confirmed in Japan, in spite of the abundance of human tick bites by this species. Accordingly, the spirochetes of I. ovatus are thought to be a variant of B. burgdorferi with low virulence.

To determine the vectors of Lyme borreliosis in Japan, the ixodid ticks taken in Hokkaido, Fukushima, Nagano, Ehime, and Kochi Prefectures were examined individually for spirochetal infections by culturing their midgut tissues in BSK medium. The cultivable spirochetes identified as Borrelia burgdorferi were detected in Ixodes persulcatus Schulze adults (15.5% of 634), nymph (6.7% of 15) and Ixodes ovatus Neumann adult (9.6% of 188) from Hokkaido, I. ovatus adults (25.5% of 47) from Fukushima, and I. persulcatus adults (21.7% of 143) and I. ovatus adults (27.1% of 85) from Nagano. However, 72 Haemaphysalis spp. from Ehime and Kochi were free from spirochetal infection. I. persulcatus is a vector of Lyme borreliosis in the Far East, but in Japan, I. ovatus may also transmit the spirochetes to human and feral animals.

A total of 59 strains ofRickettsia tsutsugamushi were isolated from patients (24 isolates), Apodemus speciosus mice (30 isolates), and unfed larvae of Leptotrombidium scuteUlare (2 isolates) and Leptotrombidium paUlidum (3 isolates) in the Gotenba-Oyama District, Shizuoka Prefecture, Japan. All these isolates were classified into the three serotypes Karp, Kawasaki, and Kuroki based on reactivity with strain-specific monoclonal antibodies. Kawasakiand Karp-type rickettsiae were isolated from L. scuteUlare and L. paUlidum, respectively, and the geographic distribution of patients and rodents infected with these two types of rickettsiae coincided with the areas densely populated by the respective chiggers. From these results, we conclude that Kawasaki-type rickettsiae are transmitted by L. scuteUlare and Karp-type ones are transmitted by L. paUlidum. Kawasaki-type rickettsial infections were prevalent in early autumn, and Karp-type infections showed a peak of occurrence in the late autumn, reflecting the seasonal fluctuations of L. scuteUlare and L. paUlidum. Isolates of Kuroki-type rickettsiae were obtained only from four patients in October and November, and the relationship between this type of rickettsia and its vector species could not be fully defined.

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