Viral haemorrhagic septicaemia virus (VHSV) has, in recent decades, been isolated from an increasing number of free-living marine fish species. So far, it has been isolated from at least 48 fish species from the northern hemisphere, including North America, Asia and Europe, and fifteen different species including herring, sprat, cod, Norway pout and flatfish from northern European waters. The high number of VHSV isolations from the Baltic Sea, Kattegat, Skagerrak, the North Sea and waters around Scotland indicate that the virus is endemic in these waters. The VHSV isolates originating from wild marine fish show no to low pathogenicity to rainbow trout and Atlantic salmon, although several are pathogenic for turbot. Marine VHSV isolates are so far serologically indistinguishable from freshwater isolates. Genotyping based on VHSV G- and N-genes reveals four groups indicating the geographical origin of the isolates, with one group representing traditional European freshwater isolates and isolates of north European marine origin, a second group of marine isolates from the Baltic Sea, a third group of isolates from the North Sea, and a group representing North American isolates. Examples of possible transfer of virus from free-living marine fish to farmed fish are discussed, as are measures to prevent introduction of VHSV from the marine environment to aquaculture.

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...

No abstract

No abstract

ABSTRACT-An epidemiological survey of the fish diseases lymphocystis, epidermal papilloma and skin ulcers in common d a b Limanda limanda L. was conducted in the southern Kattegat each year in May from 1984 to 1993. During the period of investigation, severe oxygen depletion occurred in late summer 1986 and 1988. After the oxygen deficiency in 1986. the occurrence of lymphocystis and epidermal papilloma increased and peaked in 1989 with prevalences of 14 7 and 3.3%, respectively. The prevalence of skin ulcers never exceeded 0.6 %. The relative nsk of contracting lymphocystis increased significantly from 1987 to 1991 compared with 1984 to 1986, the p e r~o d prior to the severe oxygen depletion. A significant increase in the relative risk of contracting epidermal papilloma was observed from 1987 to 1990. Females were 3 times more likely to contract this disease than males. The relative risk of skin ulcers did not change significantly during the investigation period. The prevalence of lymphocystis and epidermal papilloma was negatively correlated with the minimum oxygen levels measured in August and September the previous year; this negative correlation was significant ( p c 0.05) for lymphocystis in September, while not for epidermal papilloma ( p < 0.1). The prevalence of lymphocystis and epidermal papilloma was significantly correlated ( p < 0.01). No significant correlation was observed between stock density (expressed as catch per unit effort) a n d the diseases in question. It is probably the stress caused by the oxygen deficiency -especially the sublethal levels -that triggered the outbreak of the 2 viral diseases lymphocystis and epidermal papilloma.