Geographical Distribution of the Herpes Simplex Virus Type 1 BgKL Variant in Japan Suggests Gradual Dispersion of the Virus from Shikoku Island to the Other Islands

Restriction endonuclease fragment length polymorphism (RFLP) is useful for the epidemiological study of herpes simplex virus type 1 (HSV-1). We report here the identification of a major BglII RFLP variant of HSV-1, designated BgK L , found in 27.0% of 636 HSV-1 clinical isolates. We have also established its geographic distribution in Japan. BgK L has an unusually large BglII K fragment. SalI cleavage analyses showed that 97% of BgK L variant isolates lack both the SalI C-J and the F-J cleavage sites and have an unusually large SalI D or E fragment, and 91% of the BgK L variants lack both SalI G and H fragments. Furthermore, 96% of BgK L isolates have an unusually small KpnI M fragment. Therefore, BgK L is a marker for these five mutations in most HSV-1 isolates and is a useful HSV-1 RFLP marker. The BgK L variant was found in 59% of HSV-1 isolates from Shikoku Island, 44% of HSV-1 isolates from the Chugoku region of Honshu Island, 31% of HSV-1 isolates from Kyushu Island, 0% of HSV-1 isolates from Okinawa Island, 49% of HSV-1 isolates from Osaka, 27% of HSV-1 isolates from Shiga, 13% of HSV-1 isolates from the Chubu Region, and 9% of HSV-1 isolates from the Tohoku Region of Honshu Island. Differences in the frequency of BgK L between the Shikoku-Chugoku-Osaka area (49%) and Kyushu, between Kyushu and Okinawa, between the Shikoku-Chugoku-Osaka area and Shiga, and between Shiga and Tohoku are all statistically significant. The BgK L frequency decreases in a geographical gradient suggest that this HSV-1 variant was dispersed from Shikoku to the surrounding regions and then to more distant regions. The BgK L frequency in Tokyo was similar to the nationwide average. These are the first data to suggest a geographic and demographic dispersion pattern of HSV-1. Implications for the epidemiology and diversification of HSV-1 are discussed.