Diversity in clinical isolates of Ictalurid herpesvirus 1 (IcHV1) from U.S. farm-raised catfish and virulence assessment in channel and channel x blue catfish hybrids

Authors: VENUGOPALAN, ARUN - Mississippi State University; WHITE, DANIELLE - Mississippi State University; LOPEZ-PORRAS, ADRIAN - Mississippi State University; FORD, LORELEI - Mississippi State University; WARE, CYNTHIA - Mississippi State University; LEWIS, MARSHA - Mississippi State University; STEADMAN, JAMES - Mississippi State University; KHOO, LESTER - Mississippi State University; Richardson, Brad; WALKER, CHARLES - Mississippi State University; BYARS, TODD - Mississippi State University; WISE, DAVID - Mississippi State University; GRIFFIN, MATT - Mississippi State University; HANSON, LARRY - Mississippi State University

Submitted to: Journal of Fish Diseases
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/25/2024
Publication Date: 8/11/2024
Citation: Venugopalan, A., White, D., Lopez-Porras, A., Ford, L., Ware, C., Lewis, M.A., Steadman, J.M., Khoo, L.H., Richardson, B.M., Walker, C.M., Byars, T.S., Wise, D.J., Griffin, M.J., Hanson, L.A. 2024. Diversity in clinical isolates of Ictalurid herpesvirus 1 (IcHV1) from U.S. farm-raised catfish and virulence assessment in channel and channel x blue catfish hybrids. Journal of Fish Diseases. https://doi.org/10.1111/jfd.14005.
DOI: https://doi.org/10.1111/jfd.14005

Interpretive Summary: Ictalurid herpesvirus 1 (IcHV1) is the primary virus found in U.S. catfish industry. Unfortunately, little is known about the genetic diversity of this virus, which could influence the effectiveness of therapeutics. In this study, scientists from Mississippi State University and the USDA-ARS Warmwater Aquaculture Research Unit in Stoneville, MS investigated the genetic diversity of IcHV1 collected from U.S. catfish aquaculture facilities, to better understand the breadth of viral strains that may be encountered throughout the industry. The study identified two distinct genotypes, which also showed differing levels of mortality with genotype 2 (IcHV1B) being more virulent than genotype 1 (IcHV1A). However, survivors were resistant to a secondary exposure to both strains. The study concludes that both, channel and hybrid catfish, are susceptible to IcHV1 regardless of genotype, but that IcHV1B is more virulent than IcHV1A.

Technical Abstract: Ictalurid herpesvirus 1 (IcHV1) is the most significant viral agent in U. S. catfish aquaculture. Little is known regarding the genetic stability and antigenic variability of IcHV1. Herein, the genetic and antigenic diversity of IcHV1 field isolates was assessed by restriction fragment length polymorphism (RFLP) analysis and serum neutralization assays. RFLP analysis identified two distinct genotypes (IcHV1A and IcHV1B), both discrete from Blue Catfish Alloherpesvirus (BCAHV). Neutralization assays with anti-IcHV1 monoclonal antibody Mab-95 indicate shared antigenic determinants for IcHV1A and IcHV1B that are absent from BCAHV, which Mab-95 did not neutralize. Virulence assessments with representative isolates demonstrate significant differences between isolates within RFLP groups and pooled RFLP group data suggest IcHV1B (pooled survival [mean ± SE]: 58.3% ± 2.6) may be more virulent than IcHV1A (survival: 68.6% ± 2.4). Rechallenges with representative IcHV1A and IcHV1B isolates indicate a cross-protective effect, with fish surviving initial exposure to IcHV1A or IcHV1B showing robust protection (relative percent survival: 80-100%) when subsequently re-exposed to IcHV1A or IcHV1B. This work demonstrated that there were significant differences in virulence between case isolates, identified two separate IcHV1 lineages, distinct from BCAHV, with similar virulence in channel and channel x blue catfish hybrids and exposure to either lineage resulted in cross-protection.