Quantifying the impact of temperature variation on birnavirus transmission dynamics in hard clams Meretrix lusoria

Susceptibility of hard clams Meretrix lusoria to birnavirus (BV) infections caused by temperature variations, from a mechanistic perspective, has rarely been explored. We used a deterministic susceptible-infectious-mortality (SIM) model to derive temperature-dependent key epidemiologic parameters based on data sets of viral infections in hard clams subjected to acute temperature changes. To parameterize seasonal pattern dependence, we estimated monthly based cumulative mortality and basic reproduction numbers (R₀ ) between 1997 and 2017 by way of statistical analysis. Two alternative disease control models were also proposed to assess status of controlled temperature-mediated BV infection by using, respectively, control reproduction number (R_C )-control line criterion and removal strategy-based control measure. We showed that based on R_C -control strategy, when temperatures ranged from 15 to 26.8°C, proportion of susceptible hard clams removed should be at least 0.22%. Based on removal-control strategy, we found that by limiting pond water temperature to 25-30°C, together with increased removal rates and periods to remove hard clams, it is better to remove hard clams from June and August to reduce both mortality rate and spread of BV. Our results can be used to monitor BV transmission potential in hard clams that will contribute to government control strategy to eradicate future BV epidemics.