Massive branchial henneguyosis of catfish: A distinct, myxozoan-induced gill disease caused by severe interlamellar Henneguya exilis infection in catfish aquaculture

Authors: STILWELL, JUSTIN - Mississippi State University; GRIFFIN, MATT - Mississippi State University; LEARY, JOHN - University Of Georgia; KHOO, LESTER - Mississippi State University; CAMUS, ALVIN - University Of Georgia

Submitted to: Veterinary Pathology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/12/2024
Publication Date: 6/12/2024
Citation: Stilwell, J.M., Griffin, M.J., Leary, J.H., Khoo, L.H., Camus, A.C. 2024. Massive branchial henneguyosis of catfish: A distinct, myxozoan-induced gill disease caused by severe interlamellar Henneguya exilis infection in catfish aquaculture. Veterinary Pathology. 61(6)965-972. https://doi.org/10.1177/03009858241259181.
DOI: https://doi.org/10.1177/03009858241259181

Interpretive Summary: Proliferative Gill Disease (PGD), caused by the myxozoan parasite Henneguya ictaluri, causes a parasitic infection of catfish gills that reduces health and can cause economic losses to producers. Recently, researchers at Mississippi State University and the University of Georgia have identified a second species, Henneguya exilis, that causes a similar infection called massive branchial henneguyosis in channel catfish and channel x blue catfish hybrids. Sometimes the infections are a mixture of both Henneguya species, but the infections in hybrid catfish lead increase producer concerns. The research data provides clarity in diagnosing the disease and managing emerging health threats in aquaculture.

Technical Abstract: Proliferative gill disease (PGD), caused by the myxozoan Henneguya ictaluri, has been the most notorious parasitic gill disease in the US catfish aquaculture industry. In 2019, an unusual gill disease caused by massive burdens of another myxozoan, Henneguya exilis, was described in channel (Ictalurus punctatus) × blue (Ictalurus furcatus) hybrid catfish. Targeted metagenomic sequencing and in situ hybridization (ISH) were used to differentiate these conditions by comparing myxozoan communities involved in lesion development and disease pathogenesis between massive H. exilis infections and PGD cases. Thirty ethanol-fixed gill holobranchs from 7 cases of massive H. exilis infection in hybrid catfish were subjected to targeted amplicon sequencing of the 18S rRNA gene and compared to a targeted metagenomic data set previously generated from clinical PGD case submissions. Furthermore, serial sections of 14 formalin-fixed gill holobranchs (2 per case) were analyzed by RNAscope duplex chromogenic ISH assays targeting 8 different myxozoan species. Targeted metagenomic and ISH data were concordant, indicating myxozoan community compositions significantly differ between PGD and massive branchial henneguyosis. Although PGD cases often consist of mixed species infections, massive branchial henneguyosis consisted of nearly pure H. exilis infections. Still, H. ictaluri was identified by ISH in association with infrequent PGD lesions, suggesting coinfections occur, and some cases of massive branchial henneguyosis may contain concurrent PGD lesions contributing to morbidity. These findings establish a case definition for a putative emerging, myxozoan-induced gill disease of farm-raised catfish with a proposed condition name of massive branchial henneguyosis of catfish (MBHC).