A tale of three established pathogens: Lessons learned from trials of dealing with Mcer, Rsal and VHS in Michigan waters

Session: 01. - Disease, Parasites, and Pathogens of the Great Lakes and Freshwater Ecosystems

Gary Whelan, MI DNR Fisheries Division, [email protected]

Abstract

Seven lessons for the future will be highlighted from the experiences with three pathogens.  Whirling disease (Myxobolus cerebralis) arrived in the US in 1956 and Michigan in the late 1960s from private aquaculture (1).  While in a few watersheds, an attempt to eliminate this parasite in the early 1970s in the Tobacco River using a combination of chlorination and rotenone treatments three times in three years failed (2).  This pathogen is found in about 10% of Michigan’s trout streams and appears limited by the lack of a susceptible intermediate host (3).   Bacterial kidney disease (Renibacterium salmoninarum) has been in Michigan since 1950 with widespread population effects in Great Lakes salmonids seen in the 1980s and 1990s (4).  A control strategy based on herd immunity using from hatchery fish has taken prevalence rates from near 100% to below 5% and mortalities to zero (5).  Viral hemorrhagic septicemia virus arrived in Great Lakes waters about 2002 and caused large fish kills by the mid 2000s in an odd array of species (6).  It still causes fish kills as immune responses decline over time (7).   It is critical to  fisheries management efforts that pathogens be understood and the lessons of past (mis)adventures learned.