In vitro antiviral activity against herpes simplex virus in the abalone Haliotis laevigata

As viruses are extremely abundant in oceans, marine organisms may have evolved novel metabolites to protect themselves from viral infection. This research examined a well-known commercial gastropod, abalone (Haliotidae), which in Australia have recently experienced disease due to a neurotropic infection, abalone viral ganglioneuritis, caused by an abalone herpesvirus (AbHV). Due to the lack of molluscan cell lines for culturing AbHV, the antiviral activity of the abalone Haliotis laevigata was assessed against another neurotropic herpesvirus, herpes simplex virus type 1 (HSV-1), using a plaque assay. The concentration range at which abalone extract was used for antiviral testing caused minimal (%) mortality in Vero cells. Haemolymph (20 %, v/v) and lipophilic extract of the digestive gland (3000 μg ml⁻¹) both substantially decreased the number and size of plaques. By adding haemolymph or lipophilic extract at different times during the plaque assay, it was shown that haemolymph inhibited viral infection at an early stage. In contrast, the antiviral effect of the lipophilic extract was greatest when added 1 h after infection, suggesting that it may act at an intracellular stage of infection. These results suggest that abalone have at least two antiviral compounds with different modes of action against viral infection, and provide a novel lead for marine antiviral drug discovery.