Estimating the basic reproduction number and final epidemic size of white spot syndrome virus outbreak in Penaeus japonicus in aquaculture ponds

White spot syndrome virus (WSSV) triggers white spot disease and high mortality in farmed shrimp. To control the WSSV epidemic, understanding its dynamics through epidemiological analysis is essential. However, measuring the mortality by WSSV infection is difficult due to the rapid increase in mortality and the availability of epidemiological data on WSSV epidemics in aquaculture ponds is limited. In this study, we conducted an epidemiological analysis using field data collected during the early phase of the outbreak to estimate the complete picture of the outbreak. Thereafter, we constructed a mathematical model describing the WSSV epidemic in aquaculture ponds and fitted our model with data on WSSV outbreaks among kuruma shrimp (Penaeus japonicus) farmed in 40,000 m2 aquaculture ponds in Japan. We estimated the basic reproduction number (R0), which measures the average number of secondary infections by a single infected individual, i.e. the transmissibility of a pathogen. The estimated R0 per pond was large (3.21-4.56), suggesting that with no intervention WSSV outbreaks will likely result in large final epidemic size, with 98.0-99.7% of entire population infected by the virus. Once WSSV infection is detected in a pond, urgent intervention, such as enhanced removal of dead shrimp and harvesting all farmed shrimps immediately, is required.