Pathology and virulence of edwardsiella tarda, edwardsiella piscicida, and edwardsiella anguillarum in channel (ictalurus punctatus), blue (ictalurus furcatus), and channel (female) x blue (male) hybrid catfish

Authors: ARMWOOD, ABIGAIL - University Of Georgia; GRIFFIN, MATT - Mississippi State University; Richardson, Brad; WISE, DAVID - Mississippi State University; WARE, CYNTHIA - Mississippi State University; CAMUS, ALVIN - University Of Georgia

Submitted to: Journal of Fish Diseases
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/11/2022
Publication Date: 7/26/2022
Citation: Armwood, A.R., Griffin, M.J., Richardson, B.M., Wise, D.J., Ware, C., Camus, A.C. 2022. Pathology and virulence of edwardsiella tarda, edwardsiella piscicida, and edwardsiella anguillarum in channel (ictalurus punctatus), blue (ictalurus furcatus), and channel (female) x blue (male) hybrid catfish. Journal of Fish Diseases. 00:1-16. https://doi.org/10.1111/jfd.13691.
DOI: https://doi.org/10.1111/jfd.13691

Interpretive Summary: Disease outbreaks caused by Edwardsiella species have been detrimental to the catfish industry for decades. However, the Edwardsiella genus has undergone several reorganizations which obscure past incidents and make it difficult to determine the true culprit of previous cases. Scientists from USDA-ARS, University of Georgia, and Mississippi State University set out to evaluate differences in virulence, clinical signs, and cross-protective effects of three industry-relevant species of Edwardsiella: E. anguillarum, E. piscicida, and E. tarda. Channel, blue, and hybrid catfish were exposed to each of the three Edwardsiella pathogens at comparable doses, then monitored for 14 days. Surviving fish were later re-exposed to one of two Edwardsiella pathogens to assess cross-protection. E. piscicida was the most pathogenic, particularly in blue and hybrid catfish, causing up to 100% mortality while E. anguillarum and E. tarda showed less than 5% mortality in all catfish species. The study also showed that catfish exposed to certain Edwardsiella species had higher survival upon re-exposure, suggesting a protective immune response. This study helps in confirming the need to recognize E. piscicida as an emergent pathogen in the catfish industry, and improves our understanding of protective effects present in surviving individuals.

Technical Abstract: Edwardsiella tarda has historically been a bacterial pathogen of nominal concern in farmed catfish in the USA. In the 2010s, E. tarda was reaffiliated into three species: E. tarda, E. piscicida, and E. anguillarum, of which E. piscicida is currently recognized as a significant, emergent pathogen within the industry. This reorganization has obscured previously documented disease pathologies of these bacteria in catfish. This study clarifies discrepancies in pathologic changes and virulence of E. tarda, E, piscicida, and E. anguillarum in channel (Ictalurus punctatus), blue (I. furcatus), and channel x blue hybrid catfish and assesses potential cross-protection of Edwardsiella congeners against subsequent E. ictaluri and E. piscicida challenge. Channel, blue, and hybrid catfish (20 fish/tank; 3 tanks/treatment) were intraperitoneally challenged with varying doses of E. tarda, E. piscicida, and E. anguillarum. Bacterial and histopathology samples were collected at 1, 2, 3, 5, 10, and 14-days post challenge (dpc). Cumulative mortality was recorded for 14-dpc in separate non-sampled tanks (20 fish/tank). Cumulative mortality associated with E. piscicida challenge ranged from 25-95%, 20-55%, and 80-100% in hybrids, channels, and blues, respectively. Conversely, E. anguillarum and E. tarda produced =5% mortality, regardless of catfish species, at comparable doses. Gross changes included poor body condition, mild ascites, transmural body wall ulcerations, and, rarely, dorsocranial ulceration (hole-in-the-head). Histologic lesions were characteristic of acute gram-negative sepsis, with more severe lesions in fish infected with E. piscicida, regardless of dose. It required 100X greater doses of E. anguillarum and E. tarda to produce similar pathology. Predominant early lesions included disseminated hemorrhage and necrosis, often with numerous bacteria accompanied by gastric submucosal edema. Transition to a granulomatous response with reduced bacterial numbers began around 3-dpc and was the dominant lesion observed by 5-dpc. Lesions were uncommon in all fish surviving 14-dpc. At 100 days post-challenge, surviving fish were subsequently exposed to E. piscicida via intraperitoneal injection or E. ictaluri via 30-minute immersion bath. Hybrids previously challenged with E. piscicida or E. anguillarum were more likely to survive E. piscicida challenge than naïve controls (p < 0.01), while channels were more likely to survive an E. ictaluri challenge after E. piscicida challenge (p < 0.05). Results substantiate previous reports indicating E. piscicida is more pathogenic in catfish compared to E. anguillarum and E. tarda. Cumulative mortality varied between catfish species, with blue and hybrid catfish more severely affected, supporting previous work pointing to increased susceptibility of hybrid and blue catfish to these agents. Lastly, this work corroborates research evincing a cross-protective effect among some Edwardsiella congeners. Further work is warranted to elucidate the cross-protective nature of the immune response induced by E. anguillarum and E. piscicida against subsequent E. ictaluri and E. piscicida challenge.