Cross‐protective efficacy of a live‐attenuated Edwardsiella ictaluri vaccine against heterologous Edwardsiella piscicida isolates in channel and channel × blue catfish hybrids

Abstract

Edwardsiella piscicida is a growing problem for catfish aquaculture in the southeastern United States, particularly in channel (Ictalurus punctatus) x blue (I. furcatus) catfish hybrids. Research has shown E. piscicida isolates recovered from farmed catfish in Mississippi form at least five discrete phyletic groups, with no apparent differences in virulence in channel and hybrid catfish. Laboratory trials have shown a live‐attenuated E. ictaluri vaccine (340X2) cross‐protects against at least one E. piscicida isolate (S11–285) in channel and hybrid catfish, although it is unknown if this protection exists for other E. piscicida variants. To this end, channel and hybrid catfish were immunized by immersion with E. ictaluri 340X2. Thirty days later, fish were challenged by intracoelomic injection with representative E. piscicida variants from each phyletic group. Relative percent survival (RPS) for hybrids ranged from 54.7% to 77.8%, while RPS in channels ranged from 80.5% to 100%. A second study investigated whether channel and hybrid catfish exposed to heterologous E. piscicida isolates were similarly protected against wild‐type E. ictaluri. Fish were exposed by bath immersion to representative E. piscicida isolates from each phyletic group. Thirty days post‐immunization, fish were challenged by immersion with wild‐type E. ictaluri isolate S97–773. Regardless of variant, previous exposure to heterologous E. piscicida isolates significantly improved survival following E. ictaluri challenge. These findings suggest the presence of shared and conserved antigens among E. piscicida and E. ictaluri that could be exploited by application of polyvalent or cross‐protective vaccines.

Pathology and virulence of Edwardsiella tarda, Edwardsiella piscicida, and Edwardsiella anguillarum in channel (Ictalurus punctatus), blue (Ictalurus furcatus), and channel × blue hybrid catfish

“…This study supports previous work demonstrating improved survival in fish following exposure to E. piscicida and subsequent challenge with E. ictaluri (Griffin et al, 2020a). These findings, coupled with reports of protection conferred by a live-attenuated E. ictaluri vaccine against E. piscicida infection in channel catfish (Griffin et al, 2020a;López-Porras et al, 2022) live-attenuated E. ictaluri vaccine exists , utilization of other Edwardsiella species in a combinatory fashion may optimize protection, especially in hybrids where vaccine efficacy may wane against high doses of E. piscicida (Griffin, Greenway, et al, 2020).…”

“…Griffin et al (2020a) reported immersion in wild‐type E. piscicida produced 89%–100% relative percent survival in channel catfish exposed to E. ictaluri 35 days post‐immunization. López‐Porras et al (2022) reported similar protective effects afforded by heterologous E. piscicida isolates against E. ictaluri . While promising, results herein should be supported by more robust, replicated studies with larger sample sizes, particularly for blue catfish, which had the lowest survival in the initial challenges.…”

“…Collectively, these studies highlight the potential of E. piscicida as a vaccine candidate. Given the difficulties of inducing disease by immersion or oral delivery of wild‐type E. piscicida isolates, vaccination with E. piscicida may be less likely to induce clinical disease but immunogenicity with oral vaccination requires additional study (Griffin et al, 2020a; López‐Porras et al, 2022; Reichley, 2017). Comparably, E. anguillarum may also confer some cross‐protection but would require a significantly higher dose.…”

“…This vaccine has been adopted widely by commercial fingerling producers in the southeastern US (Hegde et al, 2022). Live‐attenuated E. ictaluri immersion vaccination is also cross‐protective against E. piscicida related mortality in channel and hybrid catfish (Griffin et al, 2020a; López‐Porras et al, 2022). Similarly, bath exposure to E. piscicida protects channel and hybrid catfish against E. ictaluri challenge (Griffin et al, 2020a; López‐Porras et al, 2022).…”

“…Live‐attenuated E. ictaluri immersion vaccination is also cross‐protective against E. piscicida related mortality in channel and hybrid catfish (Griffin et al, 2020a; López‐Porras et al, 2022). Similarly, bath exposure to E. piscicida protects channel and hybrid catfish against E. ictaluri challenge (Griffin et al, 2020a; López‐Porras et al, 2022). However, the duration of this protection remains undocumented.…”