An Investigation into the Pathogenesis of Blue Catfish Alloherpesvirus in Ictalurid Catfish

Authors: DHARAN, VANDANA - Mississippi State University; AARATTUTHODI, SUJA - Mississippi State University; KHOO, LESTER - Mississippi State University; PHELPS, NICHOLAS - University Of Minnesota; KUMAR, GANESH - Mississippi State University; STEADMAN, JAMES - Mississippi State University; Bosworth, Brian; WISE, DAVID - Mississippi State University; HANSON, LARRY - Mississippi State University

Submitted to: Journal of the World Aquaculture Society
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/18/2021
Publication Date: 4/1/2022
Citation: Dharan, V., Aarattuthodi, S., Khoo, L., Phelps, N., Kumar, G., Steadman, J., Bosworth, B.G., Wise, D., Hanson, L. 2022. An Investigation into the Pathogenesis of Blue Catfish Alloherpesvirus in Ictalurid Catfish. Journal of the World Aquaculture Society. 53:384-400. https://doi.org/10.1111/jwas.12850.
DOI: https://doi.org/10.1111/jwas.12850

Interpretive Summary: Production losses on commercial catfish farms due to various pathogens have a significant negative impact on profitability. Blue catfish alloherpesvirus (BCAHV) is an Ictalurid herpesvirus with little information available on its pathogenesis and effects on catfish production. To determine what host species BCAHV may affect, the virus was inoculated onto fish cell lines derived from various fish taxonomic families including: Ictaluridae, Cyprinidae, Centrarchidae, and Clariidae. Results demonstrated that the virus could only replicate and effect cells derived from the family Ictaluridae (the family that includes Ictalurid catfish). In a subsequent challenge study, juvenile fish from three groups of Ictalurid catfish important in U.S. aquaculture production (channel catfish, blue catfish, and channel catfish x blue catfish hybrids) were exposed to BCAHV to determine the effects of the pathogen on live fish. Mortality following exposure to BCAHV was higher in blue and hybrid catfish when compared to channel catfish, demonstrating that groups within Ictalurid catfish show differing susceptibility to the virus. Additional experiments demonstrated that effects of BCAHV on juvenile catfish survival were diminished at higher water temperatures, decreased fish densities, and as juveniles became older. Hybrid catfish have become the predominant catfish being cultured in the U.S. and the heightened pathogenicity of BCAHV in blue and hybrid catfish as observed in this study points to the potential of this virus to be a significant pathogen in intensive catfish culture.

Technical Abstract: Intensive aquaculture production systems often encounter infectious viral disease outbreaks causing substantial fish mortalities and associated economic losses. Blue catfish alloherpesvirus (BCAHV) is an Ictalurid herpesvirus with little information available on its pathogenesis. To determine the host-specificity and potential host range of BCAHV, the virus was inoculated onto various established fish cell lines belonging to families Ictaluridae, Cyprinidae, Centrarchidae, and Clariidae. The virus replication and exhibition of cytopathic effects (CPEs) were found to be restricted to cell lines from family Ictaluridae indicating the host-specificity of BCAHV. In a subsequent challenge study, channel, blue, and hybrid catfish fingerlings were exposed to BCAHV. Mortality due to virus infection was significantly higher in blue and hybrid catfish when compared to channel catfish further specifying the host preference of the virus among ictalurid catfish. Histopathology of the BCAHV infected fish revealed splenitis with severe erythrophagia. Catfish at different days of post-hatch were challenged with the virus to factor in the influence of age on BCAHV infection which demonstrated host susceptibility to BCAHV differed with age. Since BCAHV is a herpesvirus which exhibits latency, environmental factors could trigger the latent virus resulting in disease outbreaks. Temperature had a significant role in the activation and pathogenesis of BCAHV. Fish exposed to BCAHV at sustained high temperature (32ºC) had no mortality suggesting the likelihood of virus attenuation. In another challenge with different fish stocking densities to simulate crowding, the percent mortality was found to be significantly higher in densely-stocked tanks, indicating that crowding influences BCAHV-associated mortality in catfish fingerlings and horizontal transmission may be a key element in BCAHV pathogenesis. The heightened pathogenicity of BCAHV in blue and hybrid catfish as observed in this study points to the potential of this virus to be a significant pathogen in intensive catfish culture.