Ultrastructural observations on the causative agent of epitheliocystis in the brown bullhead, Ictalurus nebulosus Lesueur, from Ontario and a comparison with the chlamydiae of higher vertebrates

Abstract

Abstract. Stages of development of chlamydial organisms were found in intracellular ‘cysts’ in the epithelium of the gill lamellae of brown bullheads. Early, irregularly shaped stages with granular cytoplasm occurred in membrane‐bound vacuotes in host cells of undetermined origin. The organisms enlarged and divided within the grossly hypertrophied host cell. Dense nucleoids were first seen in single, closely packed organisms, which became enlarged and irregular in shape. Small, spherical organisms were formed from larger ones by fission and budding. Mature cysts contained many small, dense, spherical forms, each of which contained a dense central nucleoid. Fine filaments arranged perpendicular to the plasma membrane traversed the space between the inner and outer membranes of the dense spherical forms, which appeared to be the terminal stage of development. The ultrastructural features of the chlamydial agent of epitheliocystis are compared with those in other fish and with chlamydiae in higher vertebrates.