ABSTRACT: Apparent replication of small DNA-negative virus-like particles (VLPs) is described from digestive and secretory (= basiphil) cells of scallops Pecten novaezelandiae, Reeve, 1853 and toheroa Paphies ventricosum (Gray, 1843) sampled during mass mortalities, and compared with apparently healthy individuals. In scallop digestive cells with putative VLPs, endocytotic and smooth membrane vesicles increased, endoplasmic reticulum (ER) proliferated, and VLPs 22 to 30 nm across were seen in an orderly array on the surfaces of the outer nuclear membrane and along ER. Proliferating ER membranes, lined with VLPs and enclosing a dense matrix, were arranged in a reticulated configuration. The ER cisternae dilated to form vacuolar inclusions (VI) containing elongated bodies, spherical in section, in a flocculent matrix which were ornated with VLPs arrays on the external membrane. Enclosed bodies also formed by budding of cytoplasm into the VI. In scallop secretory cells VLPs replaced ribosomes on ER, and ER cisternae dilated, but VI seldom formed. Toheroa diverticular epithelium showed similar changes, but secretory cells differed in that the outer membrane of the nucleus and Golgi cisternae, rather than ER, proliferated. In addition, complete VI were apparently not formed. The cytological changes observed in both bivalves are similar to those associated with enteroviruses (Picornaviridae) and caliciviruses. The possible role of VLPs in bivalve pathology is discussed.

KEY WORDS: Scallops · clams · Diverticular disease · Virus-like particles · Picornaviruses · Caliciviruses

Published in DAO Vol. 29, No. 3 (1997) on June 19
ISSN: 0177-5103. Copyright © Inter-Research, Oldendorf/Luhe, 1997