Enhancing bacterial coldwater disease diagnosis and prevention by elucidating the predomominant Flavobacterium psychrophilum serovariants in the USA

1,2Sean M. G. Lennox, 1,2Megan A. Shavalier, 2Travis O. Brenden, 1,2Christopher K. Knupp,

3Douglas R. Call, 4Esteban Soto, 1,2,5Thomas P. Loch

 1Michigan State University - Aquatic Animal Health Laboratory, Aquatic Animal Disease Ecology Program; 2Department of Fisheries and Wildlife, Michigan State University; 3Department of Veterinary Microbiology, Washington State University; 4Department of Medicine and Epidemiology, University of California, Davis; 5Department of Pathobiology and Diagnostic Investigation, College of Veterinary Medicine, Michigan State University

ABSTRACT

Flavobacterium psychrophilum (Fp), the causative agent of bacterial coldwater disease (BCWD), generates substantial losses in trout and salmon (Family Salmonidae) aquaculture facilities and hatcheries in the USA and abroad, thereby negatively affecting food security and fishery conservation efforts.  The recently uncovered and substantial diversity of BCWD-causing Fp strains in the USA may be an important factor behind the elusiveness of effective BCWD prevention and control strategies to date.  Unfortunately, little is known about the serotypic diversity of Fp in the USA.  To address this knowledge gap and subsequently enhance vaccine development and BCWD diagnosis, 324 Fp isolates, recovered from infected fishes across the USA over a span of four decades, were analyzed using a multiplex polymerase chain reaction-based serotyping scheme.  Based upon this data set, serotype 0 was the most common of the five currently described molecular serotypes, followed by serotypes 1, 2, 4, and 3, respectively.  Analyses further revealed apparent associations of some Fp serotypes with certain host species or genera (some of which have been reported in other regions of the world) and also identified several intriguing geographical and temporal trends.  These new data, in conjunction with Fp multilocus sequence typing data, were subsequently used to guide the development of a new loop-mediated isothermal amplification (LAMP) assay that has proven capable of rapidly detecting all US Fp variants tested thus far, and, after further optimization, will enhance BCWD diagnosis in laboratory and field (i.e., “pondside”) settings.  This large-scale analysis of Fp serological diversity within the USA has highlighted important nationwide epidemiological trends that are critical not only for ongoing BCWD vaccine development, but also for improving on-site and rapid Fp diagnostic techniques. Collectively, the culmination of these improvements will mitigate BCWD associated losses in US hatcheries and aquaculture facilities.