Rhabdophis tigrinus (Yamakagashi) Bites in Japan Over the Last 50 Years: A Retrospective Survey

Abstract

Introduction:Rhabdophissnakes, which include 27 species, are rear-fanged venomous snakes that are widely distributed from India to East Asia and Russia. Severe envenomation byR. tigrinus(Yamakagashi snake) in Japan andR. subminiatusin Southeast Asia has been reported. The epidemiology ofR. tigrinusbites, such as geographical features, the incidence, and changes in the number of bites over time have not been comprehensively examined. Hence, we intended to clarify the epidemiological features ofR. tigrinusbites through a careful review of scientific data over the last 50 years in Japan.Methods:Patient records ofR. tigrinusbites between 1971 and 2020 at the Japan Snake Institute were examined retrospectively. The following were ascertained: patient characteristics, clinical symptoms, laboratory data, treatment-related factors, and hospital mortality. These variables were compared in the antivenom and the without-antivenom groups.Results:Over the 50-year study period, 43R. tigrinusbites, including five fatal cases, were encountered. Severe cases ofR. tigrinusbites have been treated with antivenom since 1985; however, fatalities occurred in 2006 and 2020.R. tigrinusbite cases have been well-distributed in the western part of Japan since 2000. The mortality rate in the antivenom group was significantly lower in the patient group that was not administered the antivenom (0 vs. 23.8%,p= 0.048).Conclusion:This study clarified the epidemiology ofR. tigrinusbites in Japan over a 50-year period. Almost all severe cases ofR. tigrinusbites have been treated with the antivenom in the current situation, and fatalities occurred in cases not treated with the antivenom. It is important to diagnoseR. tigrinusbites in the early phase of the clinical course. The antivenom, the definitive treatment forR. tigrinusbites, is an unapproved drug. Hence, approval needs to be obtained for the drug.