Epidemiology of Viral Hemorrhagic Septicemia among Juvenile Pacific Herring and Pacific Sand Lances in Puget Sound, Washington

Chronic viral hemorrhagic septicemia virus (VHSV) infections were established in a laboratory stock of Pacific herring Clupea pallasii held in a large-volume tank supplied with pathogenfree seawater at temperatures ranging from 6.8 to 11.6°C. The infections were characterized by viral persistence for extended periods and near-background levels of host mortality. Infectious virus was recovered from mortalities occurring up to 167 d post-exposure and was detected in normal-appearing herring for as long as 224 d following initial challenge. Geometric mean viral titers were generally as high as or higher in brain tissues than in pools of kidney and spleen tissues, with overall prevalence of infection being higher in the brain. Upon re-exposure to VHSV in a standard laboratory challenge, negligible mortality occurred among groups of herring that were either chronically infected or fully recovered, indicating that survival from chronic manifestations conferred protection against future disease. However, some survivors of chronic VHS infections were capable of replicating virus upon re-exposure. Demonstration of a chronic manifestation of VHSV infection among Pacific herring maintained at ambient seawater temperatures provides insights into the mechanisms by which the virus is maintained among populations of endemic hosts. KEY WORDS: Viral hemorrhagic septicemia · VHS · Pacific herring Resale or republication not permitted without written consent of the publisherDis Aquat Org 93: [43][44][45][46][47][48][49] 2010 tion. Recognizing the unlikelihood that this narrow R 0 range persists for extended periods in dynamic natural systems like the NE Pacific, it is hypothesized that alternative or complementary VHSV perpetuation strategies exist in wild populations of Pacific herring. Thus, while only acute manifestations of VHS have been reported, lower levels of mortality are difficult to observe in the ocean, and the occurrence of subacute forms of the disease could easily go unnoticed. Recognition of subacute forms of VHS in Pacific herring, analogous to those known to occur in cultured rainbow trout Oncorhynchus mykiss in Europe (Smail 1999), could offer an alternative means by which the virus may be maintained in populations without the need for exclusive reliance on transmission of acute disease within a narrow R 0 range.Here, we report the results of long-term laboratory studies of VHSV-exposed Pacific herring that resulted in atypical disease manifestations that were characterized by tempered and prolonged mortality. The purpose of this study was to describe the kinetics of these subacute VHS outbreaks and to determine whether survivors were protected against future infections or disease. MATERIALS AND METHODSEstablishment of subacute and persistent VHSV infections. Sub-acute and persistent VHSV infections were initiated among laboratory-reared, age 1+ yr, specific pathogen-free (SPF) Pacific herring (n = 3668). The fish were housed in a 2.5 m diameter (3200 l) circular tank provided with flowing, processe...

Section: Methodsmentioning

confidence: 99%

Chronic and persistent viral hemorrhagic septicemia virus infections in Pacific herring

Hershberger

Gregg²,

Grady³

et al. 2010

Section: Population Modeling Of Diseasementioning

confidence: 99%

“…In 1997, VHSV prevalence was nearly the same in fish sampled in late March and mid-April (Table 1). Because most fish infected with VHSV will die or clear the disease in less than a month (Kocan et al 2001, Elston & Meyers 2009), many of the infected fish in the prespawning samples of 1995 and 1997 were not infected (or had died) 2 wk later when the spawning samples were collected.Disease components of the model can be used to predict changes in population biomass. During the past 2 decades, the ASA model was used 3 times in the fall to predict biomass sufficient for a sac roe fishery the following spring (1993, 1994, and 1999) in Prince William Sound.…”

mentioning

confidence: 99%

Failure of population recovery in relation to disease in Pacific herring

Marty

Hulson²,

Miller³

et al. 2010

Following an estimated 60% decline in population abundance in early 1993, recovery of the Pacific herring Clupea pallasii population of Prince William Sound, Alaska, USA, has been impaired by disease. Comprehensive epidemiological study from 1994 through 2002 validated an age-structured assessment (ASA) model of disease and population abundance; from 2003 to 2006, the impact of disease was modeled by analyzing only 2 lesions: ulcers and white foci in the heart. The ASA model identified increased natural mortality since 1993 that can be explained by (1) epidemics associated with ulcers (prevalence about 3%) and the North American strain of viral hemorrhagic septicemia virus (VHSV Type IVa; prevalence up to 14%) in 1994 and 1998 and (2) relatively high prevalence of the mesomycetozoean Ichthyophonus hoferi from 1994 through 2006, including epidemics with the greatest sample prevalence in 2001 (38%, by histopathology) and 2005 (51%, estimated histopathology prevalence). Fourteen other parasites occurred at prevalence >10%, but none were considered significant contributors to fish mortality. We predict that if natural mortality after 1994 had returned to background levels that best fit the model from 1980 to 1992 (0.25 yr -1 ), population biomass in 2006 would have been 3 times the best estimate, despite relatively poor recruitment since 1994. In conclusion, disease information can be used to explain and predict changes in populations that have confounded traditional fisheries assessment.KEY WORDS: Pacific herring · Clupea pallasii · Viral hemorrhagic septicemia virus · VHSV Type IVa · Ulcers · Ichthyophonus hoferi · Age-structured assessment model · Population-level response Resale or republication not permitted without written consent of the publisherDis Aquat Org 90: [1][2][3][4][5][6][7][8][9][10][11][12][13][14] 2010 are 3 to 5 yr old, live for about 12 yr, and weigh up to about 250 g. Mature fish spawn every year, but for reasons probably related to environmental conditions (Williams & Quinn 2000), strong year-classes recruit into the adult population only about once every 4 yr. The most accurate biomass estimates are made in early spring, when fish aggregations move to shallow waters to spawn. After spawning, fish disperse and do not reaggregate near spawning areas until late fall. Feeding is minimal during the winter (Foy & Norcross 2001).Four years after the March 1989 'Exxon Valdez' oil spill in Prince William Sound, about 60% of the Pacific herring population died during the winter of 1992/1993. 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 th...

“…Ammodytes species: A. hexapterus from the North American Pacific area (Kocan et al 2001) and A. personatus from Japan (Watanabe et al 2002). The isolation of VHSV from sand goby is the first report of VHSV isolation from a fish within the family Gobiidae.…”

Section: Vhsv Has Been Isolated From 2 Othermentioning

confidence: 99%

“…Since the first isolation from marine fish of viral haemorrhagic septicaemia virus (VHSV) from Atlantic cod Gadus morhua in 1979 (Jensen et al 1979, Jørgensen & Olesen 1987, VHSV has been isolated from an increasing number of marine fish species all over the northern hemisphere (Meyers & Winton 1995, Traxler et al 1995, Dixon et al 1997, Kent et al 1998, Mortensen et al 1999, Smail 2000, Takano et al 2000, Cox & Hedrick 2001, King et al 2001b, Kocan et al 2001, Brudeseth & Evensen 2002, Dopazo et al 2002, Olivier 2002, Watanabe et al 2002, Kim et al 2003.…”

Section: Introductionmentioning

confidence: 99%

Prevalence of viral haemorrhagic septicaemia virus in Danish marine fishes and its occurrence in new host species

Skall¹,

Olesen²,

Mellergaard³

2005

In order to analyse the occurrence of viral haemorrhagic septicaemia virus (VHSV) in the marine waters around Denmark, staff from the Danish Institute for Food and Veterinary Research participated in 5 research cruises during 1998 to 2002 as a follow-up to 4 research cruises performed in 1996 to 1997. In total, 16 655 fish were examined virologically as 3569 samples. Forty fish species and 3 invertebrate species were represented. VHSV was isolated from 133 samples representing 8 species: herring Clupea harengus, sprat Sprattus sprattus, dab Limanda limanda, flounder Platichthys flesus, plaice Pleuronectes platessa, cod Gadus morhua, sand eel Ammodytes sp. and sand goby Pomatochistus minutus. Calculations showed that VHSV was more prevalent in the Baltic Sea in an area between Zealand and the island of Bornholm and the waters surrounding Bornholm than in the Kattegat, Skagerrak and along the North Sea coast of Denmark. This is the first report on the isolation of VHSV from dab, flounder and plaice and the first publication on VHSV from sand eel from Europe and sand goby. MATERIALS AND METHODSFishing was performed as demersal trawling with a duration of between 15 min and 1 h, in the North Sea, Skagerrak, Kattegat, the Bay of Århus and the Baltic Sea (Fig. 1). The cruises took place in April/May (Dana cruises 5, 6 and 8), in November (Havfisken cruise for 1 d) and in February (Dana cruise 7), between 1998 and 2002. The sampling and virological examination were performed as reported previously (Mortensen et al. 1999, Skall et al. 2000. In brief, the samples consisted of tissue from either 1 fish or pooled material of up to 10 fish of the same species. The samples were frozen on board the ship (except for the 1 d cruise) and kept frozen until further examination. The samples were inoculated on BF-2 cells (Wolf et al. 1966) and positive samples were identified by development of cytopathic effect (CPE), with subsequent confirmation of VHSV by ELISA.VHSV prevalence (p) and the 95% confidence interval (CI 95% ) were calculated for herring, sprat, cod, dab, flounder and sand goby, based on randomly selected fish sampled in pools of 5 or 10 fish, comprising at least 30 fish in all. The following formulae were used: Estimated proportion of positive fish: p = 1 -(1 -P) 1/C . Proportion of positive pools: P = S /R, where S is the number of positive pools, R is the total number of pools and C is the number of fish in each pool (Kline et al. 1989); where P L and P U are the lower and upper limit for P, respectively. Substitute these limits for p in the equation to obtain limits for p (p L , p U ) (Hauck 1991). If S Ӎ 0, substitute E P U = 1 -0.05 1/R for p in the equation to obtain limits for p (p U ), where E P U is the exact limit for P. RESULTS AND DISCUSSIONIn total, 16 655 fish were examined virologically in 3569 samples, representing 40 fish species and 3 invertebrate species. VHSV was isolated from 132 samples consisting of 850 fish and representing 8 species (Table 1) Table 2. VHSV has been reported in At...