Venugopalan

Alloherpesviruses of Catfish – Latency, Virulence and Immunogenicity

1,2Arun Venugopalan, 2,5Matt J. Griffin, 2,3David J. Wise, 2,3Suja Aarattuthodiyil, 2,3Adrián López-Porras, 4Alvin C. Camus , 6Thomas B. Waltzek, 6Kuttichantran Subramaniam, 7Geoff Waldbieser, 8Andy Perkins, 7Bradley M. Richardson, 1Danielle’ White, 1Lorelei Ford, 7Bradley M. Richardson, 9Esteban Soto and 1Larry A. Hanson

1Department of Comparative Biomedical Sciences, College of Veterinary Medicine, Mississippi State University, Mississippi State, MS 39762; 2Thad Cochran National Warmwater Aquaculture Center, Delta Research and Extension Center, Mississippi State University, Stoneville, MS 38776; 3Department of Wildlife, Fisheries and Aquaculture, College of Forest Resources, Mississippi State University, Mississippi State, MS 39762; 4Department of Pathology, College of Veterinary Medicine, University of Georgia, Athens, GA 30602; 5Department of Pathobiology and Population Medicine, College of Veterinary Medicine, Mississippi State University, Stoneville, MS 38776; 6Department of Infectious Diseases and Immunology, College of Veterinary Medicine, University of Florida, Gainesville, FL, USA; 7USDA, Warmwater Aquaculture Research Unit, Stoneville, Mississippi State, MS 38776; 8Department of Computer Science and Engineering, Bagley College of Engineering, Mississippi State University, Mississippi State, MS 39762; 9 Department of Epidemiology and Medicine, School of Veterinary Medicine, University of California, Davis, CA 95616

ABSTRACT

Channel catfish virus (IcHV1) and the recently described blue catfish alloherpes virus (BCAHV) are alloherpesviruses associated with US catfish aquaculture. Channel catfish virus disease (CCVD) can be catastrophic, with mortality approaching 100% in severe outbreaks. Previous work reported the prevalence of latent IcHV1 in swim-up channel catfish fry to be ~10%. Restriction length polymorphism analysis (RFLP) identified two discrete genetic variants of IcHV1 among clinical isolates, although the prevalence of these newly recognized IcHV1 variants is unknown. In the current study, the genomes of representative IcHV1 variants (RFLP group 1A; RFLP group 1B) were sequenced. Two separate diagnostic assays were designed in duplex format using the SPUD internal positive control and validated following MIQE guidelines. Catfish fry were collected in 10-12 day intervals during the spawning season from six commercial hatcheries in the Mississippi Delta. At each sampling, sixty swim-up fry were collected from discrete hatching troughs and individual fry were screened for latent virus. Survey results indicate IcHV1 prevalence ranged from 0 – 96% in channel and hybrid catfish fry, depending on farm and time of sampling. These assays offer a useful research tool for investigating the epidemiology of IcHV1 in catfish aquaculture.

In addition to these works, a previously undocumented alloherpesvirus from blue catfish was identified by RFLP analysis. Neutralization assays revealed this BCAHV is refractive (Neutralization index [NI] = 0) to the anti-IcHV1 monoclonal antibody Mab 95, compared to IcHV1 (NI=1.8). The genome sequences of BCAHV and IcHV1 are colinear, yet share <94% identity. Exposure of blue catfish fingerlings to 1.3×105 TCID50/L BCAHV resulted in cumulative mortality of 51.67±0.70%, with pathologic changes consistent with CCVD. No mortality was observed in concurrently challenged channel or hybrid catfish fingerlings. Twenty-eight days post-challenge, surviving channel and hybrid catfish were exposed to 9.4×104 TCID50/L IcHV1 RFLP group 1A (LC50 dose), yielding 100% relative survival compared to naïve cohorts. Variable pathology in different hosts, coupled with reported differences in neutralizing index and genome sequence indicates BCAHV should be considered a separate species of Ictalurivirus. These studies lay the foundation for future research investigating alloherpesvirus in farm-raised catfish.