Marrowstone Marine Field Station
Disease Ecology Research at the Marrowstone Marine Field Station
Viral Hemorrhagic Septicemia (VHS)
The North American strain of VHSV (Genogroup IVA) is periodically associated with epizootics in wild marine species in the eastern North Pacific. Monospecific VHS epidemics involving wild Pacific herring were reported during 1994 in Port Fredrick (Alaska), 1993 in Prince Rupert Sound (British Columbia), and presumably 1942 in the Strait of Georgia (British Columbia). Additionally, VHS is proposed to have a great effect on unexpected population change in the PWS herring population. Epidemics of mixed host assemblages involving Pacific sardines and Pacific herring occurred during 1998-1999 in Queen Charlotte Strait (British Columbia) and 2001-2002 Kyuquot and Nootka Sounds (British Columbia); similar mixed assemblage VHS epidemics involving Pacific herring, Pacific hake, and walleye pollock occurred during 1998 in Lisianski Inlet (Alaska). Furthermore, capture and confinement of Pacific herring, Pacific sandlance, and surf smelt routinely results in locally severe VHS epidemics among the confined populations. In Pacific herring prevalence and severity of VHS decreases with age. Wild juvenile herring in Puget Sound are exposed to VHSV as early as 3 months post-hatch, shortly after their metamorphosis from larvae. As juveniles, Pacific herring are highly susceptible to VHS, with laboratory exposures resulting in 66-100% mortality. The prevalence and severity of VHSV in confined adult herring captured for spawn-on-kelp roe fisheries decreases with age, suggesting a possible mechanism of adaptive immunity in adults that originates from previous exposures to the virus, or the onset of innate resistance with adult age.