Experimental coinfection with columnaris and channel catfish virus disease in channel catfish fingerlings

Authors: Lafrentz, Benjamin; Abernathy, Jason; HARRISON, COURTNEY - Auburn University; Wise, Allison; VULGAR, BRENT - Auburn University; Beck, Benjamin; BRUCE, TIMOTHY - Auburn University

Submitted to: Fish Farming News
Publication Type: Popular Publication
Publication Acceptance Date: 5/4/2024
Publication Date: 5/30/2024
Citation: LaFrentz, B.R., Abernathy, J.W., Harrison, C.E., Wise, A.L., Vuglar, B.M., Beck, B.H. and Bruce, T.J. Experimental coinfection with columnaris and channel catfish virus disease in channel catfish fingerlings. Fish Farming News 2024(1):9-10. 2024. (Popular Publication)

Interpretive Summary:

Technical Abstract: Bacterial pathogens are a significant concern for Mississippi and west Alabama catfish producers. The primary bacterial pathogens encountered are Flavobacterium covae (columnaris disease; previously under F. columnare), Aeromonas hydrophila (motile Aeromonad septicemia), and Edwardsiella ictaluri (hole-in-the-head disease). These diseases can move quickly through ponds, and it’s critical to understand the mechanics of these infections. In addition to bacterial pathogens, channel catfish virus (CCV) can also be an issue in production, and it primarily occurs in juveniles. This virus primarily impacts fingerlings during the summer when water temperatures are hot. For clinical signs, juvenile fish often present an extremely swollen abdomen, petechial hemorrhaging, and yellow mucus through the gastrointestinal tract. Although this virus has been researched for decades, several questions remain regarding pathogenesis, including the ability to be coinfective with other catfish pathogens. In aquaculture, bacterial coinfections exist when an animal is affected by one or more pathogens, and this may be any combination of bacterial, viral, or parasitic. A recent study was conducted to evaluate the dynamics of coinfection with F. covae and CCV in juvenile channel catfish. The primary objective was to evaluate the influence of a mixed infection on mortality. Additionally, samples were collected to evaluate changes to the host immune response and physiology via transcriptomic analysis of spleen and kidney tissues. With this design, single infections of F. covae (isolate ALG-00-530) and CCV (isolate 2013-CCV-DRB) and a coinfection dose (both pathogens simultaneously) were used to experimentally infect fingerlings. The CCV isolate was recovered from archived frozen hybrid catfish from a diagnostic case in 2013 and was shown to be exceptionally virulent. The catfish were challenged using an immersion model in a biosecure laboratory at the E.W. Shell Research Center (Auburn University). The catfish were exposed to each pathogen combination for a period of 1h. Following exposure, the tanks were provided with 28°C flow-through water, and mortalities were collected and necropsied twice daily. After 13 days of observation, the single F. covae infection group had a total cumulative percent mortality (CPM) of 21.3 ± 6.7 %. The single-infection CCV group was 77.0 ± 9.2 %. A coinfection half-dose combination of each pathogen demonstrated pronounced mortality (100.0 ± 0.0 %). Trial results indicate changes in catfish mortality levels and survival trends from simultaneous exposure to this bacterial/viral infection. The project team is also finalizing transcriptomic analyses of catfish collected during the challenge period. This will allow us to understand how these pathogens influence changes to gene expression and the catfish immune response during this exposure. For the pond culture of catfish, there are many different avenues of pathogen transmission, and the system's open nature allows diseases to spread quickly. By understanding the complex interactions of infections involving multiple pathogens, more customized and effective treatments, and mitigation strategies can be implemented at the production level.