Evaluation of the Efficacy of Iodophor Disinfection of Walleye and Northern Pike Eggs to Eliminate Viral Hemorrhagic Septicemia Virus

Abstract

Viral hemorrhagic septicemia virus (VHSv) is a serious fish pathogen that has been responsible for large-scale fish kills in the Great Lakes since 2005 (Elsayed and others, 2006; Lumsden and others, 2007; Groocock and others, 2007; Winton and others, 2007). The virus is a member of the family Rhabdoviridae, which includes other highly virulent fish pathogens such as infectious hematopoietic necrosis and spring viremia of carp virus (Winton and others, 2008), and it is listed by the World Organization for Animal Health as a reportable pathogen (Animal and Plant Health Inspection Service, 2006; World Organization for Animal Health, 2007). The virus causes high mortality and resulting outbreaks have severe economic consequences for aquaculture. Direct losses in aquaculture facilities can occur from quarantines of affected fish, depopulation and disinfection, and facility closures following detection of VHSv (Bebak, 1998). Genetic analysis of the Great Lakes VHSv isolate indicated that it was distinct from genotypes previously isolated in Europe, North America, Japan, or Korea. It was, therefore, subsequently classified as Genotype IVb (Winton and others, 2008; Bowser, 2009). By 2007, VHSv had been isolated from 25 fish species (for example, muskellunge, Esox masuqinongy, and freshwater drum, Aplodinotus grunniens) from the St. Lawrence River, Lake Ontario, Lake St. Clair, Lake Huron, and Lake Michigan (near Green Bay, Wis.), as well as from inland waters in Michigan, New York, and Wisconsin. Viral hemorrhagic septicemia virus was also isolated from wild muskellunge collected as broodstock from Clear Fork Reservoir, Ohio in 2008 and from sea lamprey, Petromyzon marinus, from northern Lake Huron. External clinical signs of a VHSv infection include hemorrhaging (“redness”) of the skin, swollen abdomen, or exopthalmia (“pop-eye”; fig. 1). Hemorrhages can also be present internally in the liver, spleen, intestines, or musculature (fig. 2). Outbreaks of VHSv in the Great Lakes raised concerns regarding VHSv introduction to public hatcheries and private fish farms as well as inland waters within and outside the Great Lakes region. In response, the U.S. Department of Agriculture Animal Plant Health Inspection Service (APHIS) implemented an interim rule in October 2006 that restricted the transfer of fish out of Great Lakes States (APHIS, 2006). Species affected by the APHIS rule included muskellunge, northern pike, Esox lucius, yellow perch, Perca flavescens, walleye, Sander vitreum, round goby, Neogobius melanostomus, and others known to be susceptible to VHSv (Bowser, 2009). The interim rule sought to reduce transmission of VHSv via fish shipments from Great Lakes States to elsewhere in the United States. Since the 1970s, iodophor disinfection of salmonid eggs has been a standard hatchery practice used to reduce the risk of pathogen transfer through ovarian or seminal fluids during gamete collection (“spawning”) operations. This long history of effective use has made iodophor disinfection a leading candidate for reducing VHSv transmission during and after gamete collection from nonsalmonid fishes. However, before iodophor egg disinfection is incorporated as a standard practice in gamete collection from nonsalmonid fishes, the safety and effectiveness needs to be evaluated. The primary objective of this study was to assess the efficacy of iodophor disinfection for eliminating VHSv (strain IVb) from fertilized eggs of walleye and northern pike intentionally challenged with VHSv following egg fertilization. A secondary objective was an assessment of the survival (hatch) of walleye and northern pike eggs following iodophor egg disinfection. Figure 1. Yellow perch exhibiting signs of viral hemorrhagic septicemia, including hemorrhages, “pop-eye,” and distended abdomen.