Experimental Transmission of VHSV Genotype IVb by Predation

Abstract

Preliminary surveillance of wild baitfish during the 2006 viral hemorrhagic septicemia virus genotype IVb (VHSV IVb) outbreaks indicated Emerald Shiners Notropis atherinoides and Bluntnose Minnow Pimephales notatus were infected with high levels of VHSV without showing clinical signs of disease. The movement and use of baitfish was recognized as the most probable vector for the introduction of VHSV to inland waters, such as Conesus Lake and Skaneateles Lake in New York, Budd Lake in Michigan, and Little Lake Butte des Morts and Lake Winnebago in Wisconsin. While numerous government agencies implemented restrictions to stop the movement of potentially infected baitfish into new waters and prevent the spread of VHSV IVb, until now, studies to investigate whether these initial introductions were by an oral route of infection have not occurred. Our studies identified infected Fathead Minnow Pimephales promelas as suitable vectors for transmitting VHSV IVb when fed to Tiger Muskellunge ( ♂ Northern Pike Esox lucius × ♀ Muskellunge Esox masquinongy) during laboratory trials. Six of 16 Tiger Muskellunge were infected with VHSV IVb after consumption of infected Fathead Minnows when assayed with quantitative reverse transcriptase polymerase chain reaction and viral isolation in cell culture. Weekly sampling of water and feces from these Tiger Muskellunge individually reared showed intermittent shedding of VHSV IVb. Those exposed to similarly VHSV IVb-inoculated fathead minnows by cohabitation only became infected in 1 case out of 16. A similar trial of 12 Tiger Muskellunge fed Round Goby Neogobius melanostomus that survived a VHSV IVb immersion challenge did not result in infection. Overall, our findings imply that consumption of infected wild baitfish may be a risk factor for introduction of VHSV.

Review of infectious agent occurrence in wild salmonids in British Columbia, Canada

“…Clinically affected fish and covert carriers can be VHSV reservoirs (Skall, Olesen, & Mellergaard, ). Waterborne transmission is the natural and predominant route of VHSV infection (Hershberger et al, ); however, predation of infected fish cannot be excluded as a potential transmission route (Getchell et al, ; Schönherz, Lorenzen, & Einer‐Jensen, ).…”

Goldfish Carassius auratus susceptibility to viral hemorrhagic septicemia virus genotype IVb depends on exposure route

“…Including earlier sampling time points and the addition of gill, skin, or intestine samples in future susceptibility trials may be warranted. The very limited evidence of disease (clinical signs only) in Expt 4 contrasted with the success in transmitting VHSV by feeding infected live baitfish to tiger muskel lunge (Getchell et al 2013). Clinical signs and histopathological changes associated with VHS are variable and cannot be used for definitive diagnosis.…”

“…Recently, an oral transmission route was demonstrated for rainbow trout (Schönherz et al 2012) and tiger muskellunge (Getchell et al 2013). A diverse number of animals, such as amphipod crustaceans (Faisal & Winters 2011), leeches (Faisal & Schulz 2009), freshwater turtles (Good win & Merry 2011), and piscivorous birds (Peters & Neukirch 1986), have been reported by several investigators as possible vectors, in addition to ballast water and boating (Bain et al 2010).…”

“…A diverse number of animals, such as amphipod crustaceans (Faisal & Winters 2011), leeches (Faisal & Schulz 2009), freshwater turtles (Good win & Merry 2011), and piscivorous birds (Peters & Neukirch 1986), have been reported by several investigators as possible vectors, in addition to ballast water and boating (Bain et al 2010). However, the movement of infected fish, for example baitfish (Goodwin et al 2004, Getchell et al 2013, Phelps et al 2013, represents a risk factor for introducing VHSV to new areas (VHSV Expert Panel and Working Group 2010). Goldfish Carassius auratus are capable of adapting to a range of habitats worldwide and expanding to new environments where they may introduce exotic diseases.…”

Potential Reservoirs and Risk Factors for VHSV IVb in an Enzootic System: Budd Lake, Michigan

“…Schönherz et al (2012) theorized that oral transmission of VHSV would be more important during initiation of infection in naive populations, whereas waterborne transfer of the virus may be more substantial once an epizootic becomes established. For enzootic systems, either oral transmission stemming from the consumption of infected individuals, including reintroduction by baitfish (Getchell et al 2013) or waterborne transmission stemming from viral shedding by infected individuals , could play roles in periodic re-emergence of the virus. Additional research clarifying the roles of these transmission routes in enzootic systems would be beneficial.…”