Shedding of OsHV-1 from infected Pacific oysters depends on viral variant

Ostreid herpesvirus-1 (OsHV-1) can cause massive economic losses of Pacific oysters, Magallana gigas. Breeding resistant oysters in the USA is difficult owing to lack of oyster hatcheries within disease-endemic locations. Without resistant oysters, understanding transmission dynamics is useful to assess the risk of disease spread to aquaculture farms. This research aimed to quantify OsHV-1 shedding from M. gigas of varying OsHV-1 susceptibility. Oyster spat were challenged with OsHV-1 to determine high and low surviving lines. Siblings were exposed as juveniles to either an OsHV-1 variant from France or San Diego, CA, USA . Oysters were injected with a known concentration of OsHV-1 and placed in individual containers. Water was sampled periodically for 6 days to monitor the amount of virus shed over time. Both family lines maintained high survival (53.3%-66.7% survival) when exposed to either variant as juveniles, indicating differences in susceptibility between ages of the same genetic line. OsHV-1 in water containing oysters exposed to the French variant was detected earlier and in significantly higher amounts overall (approx. 2.7×) than for those exposed to the San Diego variant. Peak shedding of OsHV-1 was confirmed at 24-120 h post-injection from oysters exposed to either microvariant, which improves our understanding of OsHV-1 transmission dynamics. This article is part of the theme issue 'Managing infectious marine diseases in wild populations'.