Edwardsiellosis Caused by Edwardsiella ictaluri in Laboratory Populations of Zebrafish Danio rerio

Abstract

We report the first cases of Edwardsiella ictaluri causing epizootics in laboratory populations of Zebrafish Danio rerio. Edwardsiella ictaluri is primarily recognized as a disease of catfish species and is known to cause an economically important bacterial disease of farm-raised catfish in the USA and abroad; however, it has been isolated on occasion from 10 other genera of nonictalurid fishes. We isolated E. ictaluri from moribund Zebrafish held in quarantine at two different universities in two states and from a research facility in a third state between February 23 and December 6, 2011. Edwardsiellosis in Zebrafish can be described as a severe systemic disease characterized by tissue necrosis and the presence of large numbers of extracellular and intracellular bacteria, often within macrophages. The kidneys (pronephros and mesonephros), spleen, nares, and forebrain were the most commonly and severely affected tissues. In outbreaks, mortality was acute and numerous fish died over a 1–2 week period. Mortality continued until the majority of the population was lost, at which time the remaining fish were euthanized. In addition to these cases, four cultures of bacteria isolated from Zebrafish by another diagnostic laboratory were submitted to the Louisiana Aquatic Diagnostic Laboratory for identification and were confirmed as E. ictaluri. In total, eight cultures of E. ictaluri from Zebrafish from Louisiana, Massachusetts, Pennsylvania, and Florida were identified. The isolates were confirmed as E. ictaluri by biochemical phenotype, API 20E (bioMérieux), and amplification and sequencing of a portion of the 16S rRNA gene. Edwardsiella ictaluri isolates from Zebrafish are believed to comprise a unique group and were differentiated from catfish isolates by exhibiting weaker motility, autoaggregation in broth, a different plasmid profile (two plasmids of 4.0 and 3.5 kb), a different API 20E code (4204000), and lack of lipopolysaccharide recognition with Mab Ed9.

Edwardsiella piscicida identified in the southeastern USA by gyrB sequence, species-specific and repetitive sequence-mediated PCR

“…E. ictaluri has been traditionally associated with disease outbreaks in cultured channel catfish (Hawke et al 1981, Hawke & Khoo 2004, although recently it has been implicated in mortality events in cultured tilapia Oreochromis sp. and laboratory populations of zebrafish Danio rerio (Soto et al 2012, Hawke et al 2013). E. hoshinae, first described from birds, reptiles, and aquatic environments (Grimont et al 1980), also occupies a narrow range of ecological niches, although its role in disease processes is poorly understood (Janda & Abbott 1993).…”

Real-time polymerase chain reaction assays for the detection and quantification of Edwardsiella tarda, Edwardsiella piscicida, and Edwardsiella piscicida–like species in catfish tissues and pond water

“…8,17,22 Recent reports have implicated E. ictaluri in mortality events outside the farm-raised catfish industry of the southeastern United States, suggesting a more cosmopolitan distribution than previously thought. 15,28,31 Edwardsiella tarda is the most widespread and diverse member of the genus, infecting a wide range of hosts from a variety of ecological niches. 21 Primarily thought of as a pathogen of marine and freshwater fish, E. tarda has been demonstrated to have extensive genetic and phenotypic diversity.…”

Recommendations for Health Monitoring and Reporting for Zebrafish Research Facilities

“…48 Edwardsiella ictaluri is a Gram-negative bacterium responsible for causing high mortality epizootics in zebrafish characterized by severe systemic infection with necrotizing inflammation in various visceral organs and associated morbidity and mortality. 49,50 It is transmitted by direct contact, water, feces, and orally. Although this pathogen may be susceptible…”