Epitheliocystis associated with massive mortalities of cultured lake trout Saivelinus namaycush

Abstract

The etiological agent of epitheliocystis in lake trout Salvelinus namaycush at 2 hatcheries (A and B) in the United States was investigated utilizing light, immunofluorescence, and transmission electron microscopy. Branchial inclusions observed in fish at Hatchery A were dispersed at the base of, and randomly along, the secondary lamellae. They included epithelial hyperplasia and hypertrophy, and diffuse lamellar edema and fusion. In fish at Hatchery B the branchial inclusions were located predominantly on the primary lamellae. Pathological alterations were less severe, and were characterized primarily by focal lesions of epithelial hypertrophy. The epitheliocystis particles within the branchial inclusions of fish at both hatcheries exhibited typical chlamydia morphology, size, and developmental stages. A form uncharacteristic of chlamydia was also observed. In addition, a nonchlamydia-like agent was found in branchial tissue of fish at Hatchery B. Immunofluorescent staining of infected branchial tissue with a monoclonal antibody to an antigen specific for the chlamydia genus indicated that the agents lack the lipopolysaccharide common to all known Chlamydia species. Attempts to isolate the agents in McCoy and epithelioma papillosum cyprini (EPC) cell culture systems optirnized for chlamydial growth were unsuccessful, possibly due to the poor condition of tissue samples. Massive mortalities of lake trout observed at the 2 hatcheries were associated with the epitheliocystis infections. Investigations in other laboratories failed to reveal the presence of other agents (viruses, bacteria, fungi, ectoparasites) or suboptimal conditions in water quality that might account for the mortalities. The branchial and systemic lesions observed in fish during epizootics are consonant with findings for several epitheliocystis agents and for chlamydia-like agents in other fish species.

Severe mortality in mesocosm-reared sharpsnout sea bream Diplodus puntazzo larvae due to epitheliocystis infection

“…Several authors have described significant proliferative reactions, with severe epithelial cell hyperplasia being the most common observation focused mainly in the lamellae of the gills and pseudobranch (Paperna 1977, Bradley et al 1988, Goodwin et al 2005. In other cases, the host response is benign, expressed as limited hyperplasia and encapsulation of the cyst with one or more concentric squamous epithelial layers (Turnbull 1993).…”

“…These inclusions progressively enlarge, resulting in hypertrophied cells that resemble spherical cysts. Although the pathogen cannot be cultured, and therefore Koch's postulate with experimental challenges has yet to be demonstrated, mortalities have been associated with the presence of the bacterium (Paperna 1977, Bradley et al 1988, Venizelos & Benetti 1996, Crespo et al 2001, Goodwin et al 2005. Mortalities (4 to 100%) and prevalence (20 to 100%) of the disease varies depending on fish species, developmental stage of the host, and intensity of infection.…”

Isolation of a rickettsiales-like organism from diseased coho salmon (Oncorhynchus kisutch) in Chile.

“…One chlamydia-like agent that has been reported to infect fishes is the cause of epitheliocystis in numerous species (HOFFMAN et al, 1969;MORRI SON and SHUM,1983;PAPERNA and ALVES DE MATOS,1984;ROURKE et al,1984;ZIMMER et al, 1984;BRADLEY et al,1988).…”

“…Until now, however, attempts at in vitro culture of these intracellular microorganisms, observed in fish and shellfish, have been un successful (WOLF,1981;BRADLEY et al,1988).…”

Epitheliocystis Disease in Cultured Pacu (Piaractus Mesopotamicus) in Brazil

“…Recently, most researchers (Paperna, 1977;Paperna et al, 1981;Paperna and Alves de Matos, 1984;Bradley et al, 1988;Fryer and Lannan, 1994;Groff et al, 1996;Frances et al, 1997) agree that the causative agent of the disease is a chlamydia-like organism.…”