ABSTRACT
The numbers of described species that infect molluscs are difficult to estimate because often only genus or general taxonomic group is noted. The population experienced marked mortalities, and dying oysters were found to be infected with an intranuclear, herpes-like virus. The virions were 70–90 nm diameter, nonenveloped, and hexagonal. Infected cells were found in large numbers around hemolymph sinuses. In aquaculture hatcheries, viruses have also been implicated in causing diseases of larvae. Oyster velar virus disease (OVVD) is one of the better known. Mortalities of up to 50% were observed in populations of larvae from a commercial facility where OVVD entities were present. A variety of prokaryotes are found to be associated with molluscs; many are suspected to cause diseases of the hosts, but there are few substantiated reports. The microbes include mainly Gram-negative bacteria and some Gram-positive species, as well as Rickettsiae, Chlamydiae, and Mycoplasmas.
