Meteorological factors affecting seroconversion of Akabane disease in sentinel calves in the subtropical Okinawa Islands of Japan

Akabane virus, the pathogen-causing Akabane disease, is an arthropod-borne virus (arbovirus) transmitted by the Culicoides biting midge. A nationwide serological surveillance program for bovine arboviral diseases, including Akabane disease, has been established in Japan to monitor the circulation of arboviruses by targeting sentinel calves. Okinawa, which is located in the southwestern-most region of Japan, is a high-risk area for incursion of arboviruses. The aim of the present study was to identify the meteorological factors related to farm-level seroconversion of Akabane virus by analyzing the serological surveillance data for sentinel calves collected in Okinawa between 2007 and 2015. Rainfall in winter, spring, and autumn was positively associated with seroconversion. Adequate rainfall seems to keep the soil in a suitably moist state for growth and survival of biting midges. Maximum temperature in winter was also positively associated with seroconversion in sentinel calves. The warmer temperatures in winter may provide conditions suitable for shortening the larval development cycle and increase production of adult midges. Our findings indicate that meteorological factors such as temperature and rainfall may be important factors that produce circumstances conducive to effective transmission of the virus between vectors and the host. The results of this study provide a better understanding of the circulation of arboviruses and offer suggestions for developing better surveillance and measures to prevent arboviral disease.