Chlamydiosis: a newly reported serious disease of larval and postmetamorphic bay scallops, Argopecten irradians (Lamarck)

Abstract. Diseases of bivalve molluscs characterized by the presence of prokaryotic intra-cytoplasmic inclusion bodies in epithelial cells are reviewed. The paper reports the history, clinical and pathological findings during hatchery epizootics of chlamydiosis in larval and postmetamorphic bay scallops, Argopecten irradians (Lamarck), and enzootic infection in wild, captive and cultured adult and juvenile bay scallops during a 15-year period (1972–1987) of surveillance for scallop diseases in the northeastern Atlantic coastal region of the United States. The disease was found in 44·4% of adult bay scallop laboratory accessions as an endemic disease without overt clinical signs or mortalities, and as a highly fatal epizootic disease with a rapid course in 20% of hatchery-reared larval and postmetamorphic bay scallop accessions. The pathogenesis and development of the chlamydial agent during hatchery epizootics are described. The importance of the congenital 'childhood' diseases of larval bay scallops and other species of bivalve molluscs is discussed.