Epidemiological Survey and Genomic Insights Into Ostreid Herpesvirus 1 Transmission in the Blood Clam <i>Anadara broughtonii</i> in China (2019–2025)

ABSTRACT Ostreid herpesvirus 1 (OsHV‐1) poses a major threat to bivalve aquaculture, but its impact on blood clams ( Anadara broughtonii ) remains poorly understood. This study integrated epidemiological and genomic data from 72 batches (1358 samples) collected across Chinese production systems (2019–2025). OsHV‐1 was detected in hatcheries, holding facilities, and wild populations, with high viral loads linked to mass mortalities. Prevalence was significantly higher in land‐based facilities (72%–74%) than in open‐water systems (0%–50%; p &lt; 0.001). Asymptomatic carriers, including wild populations and clams imported from the Republic of Korea, harbored lower viral loads than diseased individuals, acting as cryptic reservoirs. Temperature analysis identified disease onset at 13°C and a viral load peak at 18.9°C (95% CI: 16.4°C–22.3°C), approximately 3°C–5°C lower than those reported for oysters, reflecting host‐specific viral adaptation. Effluent from land‐based facilities tested virus‐positive, indicating a potential transmission route. Random forest analysis identified source type as the strongest predictor of infection (AUC = 0.911). Mortality risk was strongly associated with temperature (OR = 2.65, p = 0.017) and viral load (OR = 4.23, p = 0.006). Genomic analysis revealed a distinct, host‐specific lineage with no clear temporal progression. These findings demonstrate that effluent discharge, asymptomatic wild carriers, and international trade sustain OsHV‐1 endemicity in blood clam aquaculture, highlighting the need for enhanced biosecurity measures calibrated to this cold‐adapted pathosystem.