Diverse Chlamydia-like agents associated with epitheliocystis infection in two cyprinid fish species, the common carp (Cyprinus carpio L.) and the gibel carp (Carassius auratus gibelio L.)

Abstract

During a general annual fish health survey in natural waters and ponds, epitheliocystis infections were recorded in fingerlings of two cyprinid fish species, the cultured common carp and the wild gibel carp. Benign and heavy infections were equally observed without mortality. In addition to the general health inspection of fish, histopathological examinations of infected gills and molecular biological investigations of separated epitheliocysts were performed. Epitheliocysts were formed both in the interlamellar epithelial cells and in the lamella-free multilayered epithelium of the gill filaments. At the early stage of infection darkstaining inclusion bodies densely stuffed with some pathogenic agents were located at the centre of the cell, while in a progressive stage of the process inclusion bodies within the host cells were disseminated in the cytoplasm and stained pale. Molecular studies demonstrated three different agents related to Neochlamydia, Protochlamydia and Piscichlamydia based on sequence analysis of short regions of the 16S rRNA gene. Among them, Piscichlamydia is a primary fish pathogen, while Neochlamydia and Protochlamydia mostly infect free-living amoebae but have adapted thoroughly to fish.

Epitheliocystis in fish: An emerging aquaculture disease with a global impact

“…Epitheliocystis was first reported in 1920 as “mucophilosis” in the common carp ( Cyprinus carpio ) (Plehn, ); in 1969, it was described as “epitheliocystis” as an asymptomatic, chronic infection in bluegill ( Lepomus macrochirus ) (Hoffman, Dunbar, Wolf, & Zwillenberg, ). This disease has subsequently been detected in at least 90 species of fish (Nowak & LaPatra, ; Sellyei, Molnar, & Szekely, ; Stride, Polkinghorne, & Nowak, ), encompassing both bony and cartilaginous fishes (Camus, Soto, Berliner, Clauss, & Sanchez, ; Corsaro & Venditti, ; Nowak & LaPatra, ; Polkinghorne, Schmidt‐Posthaus, Meijer, Lehner, & Vaughan, ). While the health effects in wild fish are unknown, mortalities in cultured fish, especially juveniles, have been attributed to epitheliocystis (Nowak & LaPatra, ).…”

Incidence of Candidatus Piscichlamydia salmonis and Candidatus Clavochlamydia salmonicola in the farmed Brown Trout (Salmo trutta) in Ukraine.

“…Currently, there is no standard method for diagnosing epitheliocystis, especially in the early stages of the disease. In case of outbreaks of this disease, the diagnosis is made on the basis of changes in fish behavior (respiratory distress, lethargy, weak swimming behavior, growth retardation) and the presence of macroscopic tissue damage (hypertrophy and inflammation of the gills, lesions of epithelial tissues (Sellyei et al, 2017;Blandford et al, 2018), followed by microscopy of gill samples to detect cysts, then, if necessary, follow-up studies are carried out using molecular genetic methods to determine the type of specific etiological agent. Various methods have been used to detect these agents such as transmission electron microscopy (TEM), polymerase chain reaction (PCR), immunohistochemistry (IHC), in situ hybridization (ISH), but none of epitheliocystis agents have been cultured yet (Nowak & LaPatra, 2006;Seth-Smith et al, 2016;Blandford et al, 2018).…”

Microbiota associated with the skin, gills, and gut of the fish Parachondrostoma toxostoma from the Rhône basin

“…This bacterium accounted for up to 84% of the bacteria associated with gills. Candidatus piscichlamydia causes epitheliocystis inclusions in the gills and has been already detected in salmonid and cyprinid species (Draghi et al, ; Sellyei, Molnár, & Székely, ). Chlamydia ‐like pathogens have recently been detected in wild Salmo trutta in the upper Rhône (Guevara Soto et al, ) and its detection in Pt opens the need for further epidemiological investigations.…”