Association of viral hemorrhagic septicemia virus with epizootic hemorrhages of the skin in Pacific herring Clupea harengus pallasi from Prince William Sound and Kodiak Island, Alaska, USA

Abstract

Only one-third of the Pacific hernng Clupea harengus pallasi expected to spawn in Prince William Sound (PWS), Alaska, USA, in sprlng 1993 were observed. Of these herring, 15 to 43 ' % had external ulcers or subdermal hemorrhages of the skln and fins. A rhabdovirus identified as the North American strain of viral hemorrhagic septicemia virus (VHSV) was isolated from affected herring and 1 Pacific cod Gadus macrocephalus with skin lesions from PWS, and from herring with similar lesions collected near Kodiak Island. No other pathogens were detected in the herring examined. Although VHSV may have been responsible for the skin lesions, there was no confirmed mass herring mortality observed in PWS; hence the actual cause of the reduced herring numbers is still unknown. The same strain of VHSV was subsequently isolated from captive juvenile herring collected from Auke Bay, Alaska, near Juneau, from herring in British Columbia, Canada, and from Puget Sound, Washington, USA. These findings suggest the virus is an opportunistic pathogen that is widely indigenous to Pacific herring populations in the Pacific Northwest and that herring are a significant marine reservoir for North American VHSV.

Failure of population recovery in relation to disease in Pacific herring

“…ulcers and VHSV), particularly in 1994and 1998(Marty et al 2003. In the fall of 2000, however, the prevalence of Ichthyophonus hoferi increased.…”

“…Death was attributed to poor food availability in 1992, which resulted in poor fish condition the following winter (Pearson et al 1999, Elston & Meyers 2009). The weakened fish had 2 types of lesions or pathogens that are commonly associated with population stress: (1) cutaneous ulcers and (2) the North American strain of viral hemorrhagic septicemia virus (VHSV Type IVa) (Meyers et al 1994, Pearson et al 1999, Carls et al 2002). An alternative hypothesis attributes a greater proportion of the population decline to oil toxicity and overfishing in years leading up to the crash (Thorne & Thomas 2008).…”

“…In all years, the ulcer/VHSV index in Age 3 & 4 fish was greater than or about equal to the index in Age 5+ fish (Table 3). Observations of ulcers and VHSV in 1993 do not allow for a precise calculation of an ulcer/VHSV index, but available evidence (Meyers et al 1994) supports the conclusion that the index in 1993 was high (>1.0) for all ages. Therefore, changes in the ulcer/VHSV index provide evidence of a major outbreak in 1993, moderate disease in 1994 and 1998, and mild disease in 1997 and 2002 (Table 3).…”

“…This is a slight modification of the former model (Quinn et al 2001, Marty et al 2003 in which survival was linearly related to disease. The modification was made because a nonlinear relationship between survival and disease prevalence enhances estimation stability in recent versions of the model (Hulson et al 2008).Precise index information for disease in 1993 is not available because this was the first year in which the North American strain of VHSV was isolated from Pacific herring (Meyers et al 1994). Nevertheless, the fishery and survey information provided clear evidence of a large increase in natural mortality after the 1992 fisheries harvest.…”

Complementary approaches to diagnosing marine diseases: a union of the modern and the classic

“…The industry destroyed 3.8 million salmon eggs in an attempt to contain the virus [7,8]. Subsequent testing of marine species such as Pacific cod Gadus macrocephalus and Pacific herring Clupea pallasii demonstrated their infection with VHSV in wild populations [9][10][11]. Molecular tools led to a better understanding of the differences among different VHSV strains, including virulence and host susceptibilities.…”