Venugopalan

Diversity of Channel Catfish Virus (CCV) From US Farm-Raised Catfish and Virulence Assessment in Channel and Blue X Channel Catfish Hybrids

Arun Venugopalan1,2, Matt J. Griffin2,4, David J. Wise2,3, Andy D. Perkins7, Cynthia Ware2,4, Lester H. Khoo2,4, Adrián López-Porras2,3, Bradley M. Richardson6, Geoffrey C. Waldbieser6, Lorelei Ford1, Kuttichantran Subramaniam5, Thomas B. Waltzek5, Esteban Soto8, Manu Gundappa9 and Larry A. Hanson1

1Department of Comparative Biomedical Sciences, College of Veterinary Medicine, Mississippi State University, Mississippi State, MS, USA; 2Thad Cochran National Warmwater Aquaculture Center, Delta Research and Extension Center, Mississippi State University, Stoneville, MS, USA; 3Department of Wildlife, Fisheries and Aquaculture, College of Forest Resources, Mississippi State University, Mississippi State, MS, USA; 4Department of Pathobiology and Population Medicine, College of Veterinary Medicine, Mississippi State University, Stoneville, MS, USA; 5Department of Infectious Diseases and Immunology, College of Veterinary Medicine, University of Florida, Gainesville, FL, USA; 6USDA, Warmwater Aquaculture Research Unit, Stoneville, MS, USA; 7Department of Computer Science and Engineering, Bagley College of Engineering, Mississippi State University, Mississippi State, MS, USA; 8 Department of Epidemiology and Medicine, Davis-School of Veterinary Medicine, University of California, Davis, California, CA, USA; 9 The Roslin Institute and Royal (Dick) School of Veterinary Studies, University of Edinburgh, Midlothian, UK

ABSTRACT

Channel catfish virus (IcHV-1) is an alloherpesvirus endemic to catfish aquaculture in the southeastern United States. Channel catfish virus disease (CCVD) can be catastrophic, with mortality approaching 100% in severe outbreaks. First isolated in the 1970s, there is limited information regarding the virulence, genetic stability, and antigenic variability of IcHV-1 field isolates. First, twenty genomes of IcHV-1 field isolates were assembled and analyzed. Further, two qPCR diagnostic assays were designed and validated to delineate two newly recognized discrete genetic variants of IcHV1 (IcHV-1A and IcHV-1B). Next, the prevalence of latent IcHV-1 variants in catfish swim-up fry collected from six commercial hatcheries of Missississippi was estimated with qPCR assays. Finally, the virulence of IcHV-1 variants in the channel and blue x channel catfish hybrids was also assessed. Hatchery survey results indicate IcHV-1 prevalence ranged from 0 - 96% in the channel and hybrid catfish fry, depending on farm and time of sampling. Notably, no disease/mortality events were reported from cooperating laboratories, indicating IchV-1 can be present in the absence of disease. Virulence assessments with three representative isolates from each IcHV-1 group suggest that some IcHV-1B group isolates (pooled survival [mean ± SE]: 58.3% ± 2.6) may be more virulent than the IcHV-1A group (survival: 68.6% ± 2.4), with hybrids demonstrating significantly reduced survival (p<0.05) following exposure to at least one IcHV-1B isolate (C96-152). Subsequent rechallenges with representative IcHV-1A and IcHV-1B isolates indicate a cross-protective effect, with most fish surviving initial exposure to IcHV-1A or IcHV-1B isolates showing robust protection (RPS: 80-100%) when subsequently re-exposed to IcHV-1A isolate ATCC VR-665TM or IcHV-1B isolate C02-169. This work identified the existence of two discrete IcHV-1 lineages, which can induce a significant protective immune response in catfish that survive initial exposures. Rapid molecular confirmatory tests to identify IcHV-1A and IcHV-1B variants offer a helpful research tool for investigating the epidemiology of IcHV-1. Genome information, prevalence, and virulence assessments, laying the foundation for future work investigating these IcHV-1 variants' role in CCVD in catfish aquaculture.