Co-infection of Candidatus Piscichlamydia Trichopodus (Order Chlamydiales) and Henneguya sp. (Myxosporea, Myxobolidae) in Snakeskin Gourami Trichopodus pectoralis (Regan 1910).

Pattanapon Kayansamruaj,Sukkrit Nimitkul,Channarong Rodkhum,Prapansak Srisapoome,Chayanit Soontara,Nguyen Dinh-Hung,Satid Chatchaiphan,Ha Thanh Dong

doi:10.3389/fvets.2022.847977

Abstract

The present study describes a simultaneous infection of a novel Chlamydia-like organism (CLO) with a Myxozoa parasite, Henneguya sp. in snakeskin gourami Trichopodus pectoralis in Thailand. A new CLO is proposed “Candidatus Piscichlamydia trichopodus” (CPT) based on 16S rRNA phylogenetic analysis. Systemic intracellular CPT infection was confirmed by histological examination, in situ hybridization, PCR assay, and sequencing of 16S rRNA. This novel pathogen belongs to the order Chlamydiales but differs in certain aspects from other species. The histopathological changes associated with CPT infection were different from the typical pathological lesions of epitheliocystis caused by previously known CLO. Unlike other CLO, CPT localized in the connective tissue rather than in the epithelial cells and formed smaller clumps of intracellular bacteria that stained dark blue with hematoxylin. On the other hand, typical myxospores of the genus Henneguya with tails were observed in the gill sections. Infection with Henneguya sp. resulted in extensive destruction of the gill filaments, most likely leading to respiratory distress. Due to the frequency of co-infections and the unavailability of culture methods for CLO and Henneguya sp., it was difficult to determine which pathogens were directly responsible for the associated mortality. However, co-infections may increase the negative impact on the host and the severity of the disease. Given the commercial importance of the snakeskin gourami and its significant aquaculture potential, the findings of this study are important for further studies on disease prevention.

Highlights

Snakeskin gourami, Trichopodus pectoralis, is native to Southeast Asia and commonly found in the Mekong and Chao Phraya basins of Cambodia, Thailand, Southern Vietnam, and Laos [1]
We described for the first time a systemic pathology caused by a novel Chlamydia-like organism, Candidatus Piscichlamydia trichopodus and a gill parasite Henneguya sp. (Myxosporea, Myxobolidae) infecting the same fish population
Several previous studies reported that Chlamydia-like organism (CLO) can infect other cell types, including mucous cells in common carp Cyprinus carpio L. [38], pillar cells in tiger puffer Takifugu rubripes [39], macrophages in brown bullhead Ictalurus nebulosus [40] and chloride cells in Atlantic salmon Salmo salar [41]

Summary

Introduction

Trichopodus pectoralis, is native to Southeast Asia and commonly found in the Mekong and Chao Phraya basins of Cambodia, Thailand, Southern Vietnam, and Laos [1]. Myxosporeans are diverse and widespread parasites that cause severe economic damage to fish worldwide [6–8]. The genus Henneguya includes more than 200 species and is one of the most diverse myxosporean genera in the family Myxobolidae [8]. Some species of the genus Henneguya are responsible for diseases leading to high mortality rates, but most species are thought to have little or no negative impact on fish health [6, 11]. Other commonly known pathogens that cause gill cysts in fish are bacteria from the order Chlamydiales. These bacteria typically cause epithelial cysts in the skin and gills called epitheliocystis [15–17]. Unavailability of culture techniques for chlamydial pathogens has been a major obstacle for in vitro studies [15, 18]

Methods

Results

Conclusion