Infectious salmon anaemia (ISA) risk factors in sea-cultured Atlantic salmon Salmo salar

103

Infectious salmon anemia vlrus (ISAV) was isolated at a marine grow-out site in New Brunswick. Canada, from Atlantic salmon Salmo salar which experienced mortalities due to hemorrhagic kidney syndrome (HKS). Of 20 fish sampled in this study, 14 showed histologically various degrees of interstitial hemorrhaging, tubular epithelia1 degeneration and necrosis, and tubular casts in the posterior kidney, typical of HKS. Posterior kidney and spleen homogenates produced a cytopathic effect on chinook salmon embryo (CHSE-214) cells 10 to 14 d after inoculation. Pleomorphic virus particles in the size range 80 to 120 nm were seen by electron microscopy. The virus was confirmed as ISAV using reverse transcriptase-polymerase chain reaction (RT-PCR) This is a systematic diagnostic study of the isolation of ISAV on the North American continent and the first description of the growth of ISAV on the CHSE-214 cell line.

Section: Introductionmentioning

confidence: 89%

Isolation of infectious salmon anemia virus (ISAV) from Atlantic salmon in New Brunswick, Canada

Bouchard¹,

Keleher²,

Opitz³

et al. 1999

103

“…Epidemiological studies have led to the identification of risk factors for aquatic diseases including furunculosis (Aeromonas salmonicida) and infectious salmon anaemia in Atlantic salmon Salmo salar (Jarp et al 1995, Jarp & Karlsen 1997, and vibriosis in rainbow trout Oncorhynchus mykiss (Thorburn 1987).…”

Section: Introductionmentioning

confidence: 99%

Risk factors associated with white spot syndrome virus infection in a Vietnamese rice-shrimp farming system

Corsin¹,

Turnbull²,

Hảo³

et al. 2001

White spot disease (WSD) is a pandemic disease caused by a virus commonly known as white spot syndrome virus (WSSV). Several risk factors for WSD outbreaks have been suggested. However, there have been very few studies to identify risk factors for WSD outbreaks in culture systems. This paper presents and discusses the risk factors for WSSV infection identified during a longitudinal observational study conducted in a Vietnamese rice-shrimp farming system. A total of 158 variables were measured comprising location, features of the pond, management practices, pond bottom quality, shrimp health and other animals in the pond. At the end of the study period WSSV was detected in 15 of the 24 ponds followed through the production cycle (62.5%). One hundred and thirtynine variables were used in univariate analyses. All the variables with a p-value ≤ 0.10 were used in unconditional logistic regression in a forward stepwise model. An effect of location was identified in both univariate and multivariate analyses showing that ponds located in the eastern portion of the study site, closer to the sea, were more likely to test positive for WSSV by 1-step PCR at harvest. Ponds with shrimp of a smaller average size 1 mo after stocking tended to be positive for WSSV at the end of the production cycle. Average weight at 1 mo was also highlighted in multivariate analyses when considered as either a risk factor or an outcome. Other risk factors identified in univariate analyses were earlier date of stocking and use of commercial feed. A number of variables also appeared to be associated with a reduced risk of WSSV at harvest including the presence of dead post larvae in the batch sampled at stocking, presence of Hemigrapsus spp. crabs during the first month of production, feeding vitamin premix or legumes, presence of high numbers of shrimp with bacterial infection and the presence of larger mud crabs or gobies at harvest. No associations were detected with WSSV at harvest and stocking density, presence, or number or weight of wild shrimp in the pond. The multivariate model to identify outcomes associated with WSSV infection highlighted the presence of high mortality as the main variable explaining the data. The results obtained from this study are discussed in the context of WSD control and areas requiring further investigation are suggested.KEY WORDS: White spot disease · Aquatic epidemiology · Risk factors · Penaeus monodon · Rice-shrimp farming systemResale or republication not permitted without written consent of the publisher

“…Thus, the absence of disease in freshwater salmon farms is likely to be due to insufficient infectious pressure at these farms. This emphasises the importance of addressing the risk factors for ISA, which were identified by Jarp & Karlsen (1997).It was not possible to establish the minimum infective dose for i.p. infection due to the severity of challenge, in either fresh or seawater salmon, with the range of doses used in this study.…”

mentioning

confidence: 99%

Experimental infection models and susceptibility of Atlantic salmon Salmo salar to a Scottish isolate of infectious salmon anaemia virus

Raynard

Snow²,

Bruno³

2001

Infection models for both fresh and seawater salmon were established using a Scottish isolate of infectious salmon anaemia virus (ISAV). Modes of infection were intra-peritoneal injection, cohabitation and immersion exposure, and a range of doses was tested. Development of these models using a Scottish isolate of ISAV provided an approximation of the minimum infective dose leading to mortality under different infection regimens. The models also allow prediction of the time to first mortality and an estimation of expected total mortality following the various routes of infection. Such knowledge is important to the development of anti-ISAV vaccines and to future studies aimed at understanding the biology of ISAV in general. KEY WORDS: Infectious salmon anaemia virus · Atlantic salmon · Salmo salar · Experimental infection Resale or republication not permitted without written consent of the publisherDis Aquat Org 47: [169][170][171][172][173][174] 2001 MATERIALS AND METHODS Cell culture and virus propagation. The isolate of ISAV used in this study was 0390/98, which originated from a clinical outbreak of ISAV on a salmon farm in west Scotland. The salmon head kidney-1 (SHK-1) cell line was used to propagate virus for transmission experiments according to previously described methods (Dannevig et al. 1995). Harvested virus was stored at -80°C following 2 passages in SHK-1 cells. A single aliquot of virus was titrated using the tissue culture infectious dose method (TCID 50 ) (Reed & Muench 1938, Burleson et al. 1992) following a single freezethaw cycle.Pathogen-free fish. Atlantic salmon parr (mean weight 27.5 g) and Atlantic salmon post-smolts (mean weight 273 g) were reared at the FRS Marine Research Unit, Aultbea, Ross-shire, Scotland. Before the infection experiments fish were screened for the presence of ISAV, viral haemorrhagic septicaemia virus, infectious haematopoietic necrosis virus and infectious pancreatic necrosis virus by standard virology tissue culture methods as previously described (Dannevig et al. 1995, Snow & Smail 1999 and, for ISAV, by reverse transcription polymerase chain reaction (RT-PCR) (Mjaaland et al. 1997).Experimental infection with ISAV. Fish were allowed to acclimate for 7 d and starved for 24 h before all experimental infections. Water temperatures were maintained at 10°C for the duration of each experimental infection. Freshwater was supplied from Aberdeen city drinking water, which originates from the River Dee and passes through an activated carbon filter and UV treatment before entering fish tanks. Seawater was extracted from the North Sea at a salinity of 32 ‰ and passed through a sand filter and UV disinfection treatment before entering fish tanks.Experimental infection of freshwater Atlantic salmon parr with ISAV. Atlantic salmon parr were stocked in 30 l aquaria supplied with flow rates of 40 l h -1 freshwater, at a density of 15 fish per tank. Experimental infections were obtained via immersion, i.p. and cohabitation routes. Fish were anaethetised before i.p. i...