VIRUS-LIKE PARTICLES ASSOCIATED WITH CYTOPATHOLOGY IN THE DIGESTIVE GLAND EPITHELIUM OF SCALLOPS PECTEN NOVAEZELANDIAE AND TOHEROA PAPHIES VENTRICOSUM

Apparent replication of small DNA-negative virus-like particles (VLPs) is described from digestive and secretory (= basiphil) cells of scall ops Pecten novaezelandiae, Reeve, 1853 and toheroa Paphies ventricosum (Gray, 1843) sampled during mass mortalities, and compared with appar ently healthy individuals. In scallop digestive cells with putative VL Ps, endocytotic and smooth membrane vesicles increased, endoplasmic re ticulum (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 cisterna e 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 repl aced 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 cis ternae, rather than ER, proliferated In addition, complete VI were app arently not formed. The cytological changes observed in both bivalves are similar to those associated with enteroviruses (Picornaviridae) an d caliciviruses. The possible role of VLPs in bivalve pathology is dis cussed.