Viral haemorrhagic septicaemia virus (VHSV) and infectious haematopoietic necrosis virus (IHNV) are important viral pathogens posing a serious threat to salmonid fish. Survival of two isolates of IHNV and one of VHSV was assessed at temperatures ranging from 4 to 25°C: (a) after drying on stainless steel, (b) in cell culture medium, (c) in filtered river water, (d) in unfiltered river water, and (e) survival, adsorption and desorption in river sediment and five typical soil types. The viruses survived 1 hr to > 84 days depending on the conditions. Survival was inversely related to temperature and organic and inorganic content. Both viruses remained infectious after being dried on stainless steel for several weeks highlighting the risk of mechanical transmission and persistence in a dry environment. Both adsorbed to the soils from the river water inoculum, with titres between 5.56x104 and 2.58x108 TCID50 /ml after 1 hr. Clay soils adsorbed the least virus but had the greatest decrease in the river water inoculum (undetectable in ≤ 1 hr), and there was no desorption. Virus desorbed from the other soils into the surrounding water at different rates dependant on soil type (longest desorption was from chalk loam and sandy soil-detected at 28 days). When desorption was no longer detectable, virus persisted, adsorbed to the soil and remained infectious (the longest adsorption was detected in clay loam for ≥ 49 days, but all the viruses adsorbed to soils were likely to have survived longer than that detected, based on their rate of decay). The long survival of the viruses, particularly at cooler temperatures, highlights the risk of survival in the environment and waterborne spread. The data presented here are highly relevant for assessing risk of pathogen introduction via fomites (stainless steel) and for deciding on best control measures in the context of disease outbreaks.

This datasheet on grass carp haemorrhagic disease covers Identity, Overview, Associated Diseases, Pests or Pathogens, Distribution, Hosts/Species Affected, Diagnosis, Pathology, Epidemiology, Impacts, Prevention/Control, Further Information.

This datasheet on pike fry rhabdovirus disease covers Identity, Overview, Associated Diseases, Pests or Pathogens, Distribution, Hosts/Species Affected, Diagnosis, Pathology, Epidemiology, Impacts, Prevention/Control, Further Information.

This datasheet on koi herpesvirus covers Identity, Overview, Distribution, Hosts/Species Affected, Vectors & Intermediate Hosts, Further Information.

Koi herpesvirus disease (KHVD) is a herpesvirus infection that induces a lethal acute viraemia that is highly contagious in common carp (Cyprinus carpio) and varieties of C. carpio such as koi carp and ghost carp. The causative agent is classified as Cyprinid herpesvirus 3 and is transmitted horizontally and can occur directly or indirectly. The diagnostics; pathology; pathophysiology; prevention and control against KHVD are discussed.

Aquatic animal diseases are a major constraint for increasing aquaculture production. Understanding the contribution of pathogen spread from infected aquaculture sites is critical in devising control measures in the event of an outbreak. We have reviewed the available literature on the persistence in the aquatic environment of several important viral pathogens of fish and crustaceans. These include infectious haematopoietic necrosis virus, viral haemorrhagic septicaemia virus, infectious salmon anaemia virus, koi herpes virus, epizootic haematopoietic necrosis virus and infectious pancreatic necrosis virus, white spot syndrome virus (WSSV), Taura syndrome virus and yellow head virus. Some trends were common to all viruses: (i) viability declined with increasing temperature (at temperatures above 0 degrees C); (ii) higher biological loading in water correlated with reduction in detectable viable viruses; and (iii) virus decay in water is a function of time. Most aquatic animal viruses (AAVs) remained viable for several days or weeks. WSSV is particularly stable. Comparison of studies investigating survival parameters was sometimes difficult because of the different methods employed and different ways in which the data were presented. Data gaps are identified and experimental methods employed for testing critically assessed. The information presented in this review is directly relevant to design effective control measures for AAVs and to explore measures that reduce the economic impact of disease caused by these important pathogens.

This datasheet on spring viraemia of carp covers Identity, Overview, Associated Diseases, Pests or Pathogens, Distribution, Hosts/Species Affected, Diagnosis, Pathology, Epidemiology, Impacts, Prevention/Control, Further Information.

Infectious hematopoietic necrosis virus (IHNV, Rhabdoviridae), is the causative agent of infectious hematopoietic necrosis (IHN), a disease notifiable to the World Organisation for Animal Health, and various countries and trading areas (including the European Union). IHNV is an economically important pathogen causing clinical disease and mortalities in a wide variety of salmonid species, including the main salmonid species produced in aquaculture, Atlantic salmon (Salmo salar) and rainbow trout (Oncorhynchus mykiss). We reviewed the scientific literature on IHNV on a range of topics, including geographic distribution; host range; conditions required for infection and clinical disease; minimum infectious dose; subclinical infection; shedding of virus by infected fish; transmission via eggs; diagnostic tests; pathogen load and survival of IHNV in host tissues. This information is required for a range of purposes including import risk assessments; parameterisation of disease models; for surveillance planning; and evaluation of the chances of eradication of the pathogen to name just a few. The review focuses on issues that are of relevance for the European context, but many of the data summarised have relevance to IHN globally. Examples for application of the information is presented and data gaps highlighted.

Spring viraemia of carp (SVC) is a rhabdovirus infection, which has a significant economic impact in pond cultures of carp in Europe and western Independent States of the former Soviet Union. The causative agent of SVC, spring viraemia of carp virus (SVCV), has been divided into four subgroups, Ia, Ib, Ic and Id, on the basis of glycoprotein (G) protein gene sequences. In this study, a new primer set was designed from a G gene sequence of SVCV to identify the four subtypes of SVCV by reverse transcription polymerase chain reaction (RT-PCR). The specific PCR products of 369 bp were amplified from 15 SVCV isolates of all four subtypes. However, pike fry rhabdovirus (PFRV), which is antigenically related to SVCV, and other viruses antigenically related to SVCV and PFRV were not amplified. The four subtypes of SVCV were specifically amplified by the RT-PCR. Furthermore, the detection limit of the RT-PCR was 7.1 × 10(2) copies/reaction, and it was not influenced by the addition of RNA extracted from fish tissues. The RT-PCR will be applied not only to RNA extracted from viral suspensions, but also from fish tissue. It will contribute to rapid identification of SVCV in fish with clinical signs of SVC.

A qualitative import risk assessment was undertaken to assess the likelihood of introduction and establishment of viral haemorrhagic septicaemia virus (VHSV) genotype 1a in England and Wales (E&W), via the processing of imported rainbow trout (Oncorhynchus mykiss) carcasses from continental Europe. The likelihood was estimated for one import from an infected farm. Four main routes by which susceptible populations could be exposed to VHSV via processing waste were considered: (i) run-off from solid waste to watercourses, (ii) contamination of birds or rodents with VHSV by scavenging solid waste, (iii) discharge of liquid waste to mains drainage, and (iv) discharge of liquid waste directly to watercourses. Data on the biophysical characteristics of VHSV, its epidemiology, fish processing practices and waste management were collected. Likelihoods for each step of the four pathways were estimated. Pathway 4 (discharge of liquid waste to a watercourse) was judged as the most likely to result in infection of susceptible individuals. Levels of virus entering the aquatic environment via pathways 1-3 were judged to be many times lower than pathway 4 due mainly to the treatment of solid waste (pathways 1 and 2) and high levels of dilution (pathways 1, 2 and 3). Thirty-four trout farms process fish, of which seven have imported carcasses for processing. Compared with other processing facilities, on-farm processing results in a higher likelihood of VHSV exposure and establishment via all four pathways. Data availability was an issue; the analysis was particularly constrained by a lack of data on the prevalence of VHSV in Europe, volume of trade of carcasses into the UK and processing practices in E&W. It was concluded that the threat of VHSV introduction into E&W could be reduced by treatment of liquid effluent from processing plants and by sourcing carcasses for on-farm processing only from approved VHSV free areas.

Spring viraemia of carp (SVC) is a disease of international importance that predominantly affects cyprinid fish and can cause significant mortality. In the United Kingdom (UK), SVC was first detected in 1977 with further cases occurring in fisheries, farms, wholesale and retail establishments throughout England and Wales (but not Scotland, where few cyprinid populations exist, nor Northern Ireland where SVC has never been detected) over the subsequent 30 years. Following a control and eradication programme for the disease initiated in 2005, the UK was recognised free of the disease in 2010. This study compiles historic records of SVC cases in England and Wales with a view to understanding its routes of introduction and spread, and assessing the effectiveness of the control and eradication programme in order to improve contingency plans to prevent and control future disease incursions in the cyprinid fish sectors. Between 1977 and 2010 the presence of SVC was confirmed on 108 occasions, with 65 of the cases occurring in sport fisheries and the majority of the remainder occurring in the ornamental fish sector. The study found that throughout the history of SVC in the UK, though cases were widely distributed, their occurrence was sporadic and the virus did not become endemic. All evidence indicates that SVC was not able to persist under UK environmental conditions, suggesting that the majority of cases were a result of new introductions to the UK as opposed to within-country spread. The control and eradication programme adopted in 2005 was highly effective and two years after its implementation cases of SVC ceased. Given the non-persistent nature of the pathogen the most important aspect of the control programme focused on preventing re-introduction of the virus to the UK. Despite the effectiveness of these controls against SVC, this approach is likely to be less effective against more persistent pathogens such as koi herpesvirus, which are likely to require more stringent measures to prevent within-country spread.

Disposal of fish by-products in the European Community must comply with Regulation (EC) No 1069/2009 which categorizes animal by-products according to risk, and specifies methods of disposal of by-products according to that risk. There is provision under the regulation for composting or ensiling to be used for by-products from aquatic animals. Biosecurity considerations require knowledge of the parameters of time and temperature, or time and pH, required to inactivate any fish pathogens that may be present. To provide those data, we undertook laboratory studies on the inactivation of a number of fish pathogenic viruses and bacteria at 60 °C, pH 4.0 and pH 12.0 as a preliminary to conducting subsequent trials with the most resistant viruses and bacteria in fish tissues. The most resistant bacterium to 60 °C, pH 4.0 as well as pH 12.0 was Lactococcus garvieae. Its concentration was reduced to the level of sensitivity of the test after 24-48 h exposure to 60 °C, but it survived for at least 7 days at pH 4.0 and 14 days at pH 12.0. The most resistant virus to 60 °C was infectious pancreatic necrosis virus, and to pH 12.0 was infectious salmon anaemia virus. The majority of the viruses tested survived exposure to pH 4.0 for up to 28 days. The results suggest that the process of acid ensiling alone is not an effective method for the inactivation of many viral and bacterial pathogens, and fish by-products would need further treatment by a method approved under the regulation following ensiling, whereas alkaline or heat treatment are likely to provide an increased degree of biosecurity for on-farm processing of mortalities.

Movements of commodity fish present a potential risk of transferring pathogens. Within a study to estimate the risk from imported rainbow trout Oncorhynchus mykiss carcases, fry were exposed to tissue homogenates from market size rainbow trout infected experimentally with viral haemorrhagic septicaemia (VHS) by waterborne exposure to VHS virus (VHSV, isolate of genotype Ia). Tissues were collected from fish that showed clinical signs and from recent mortalities. Homogenates of (i) internal organs, (ii) brain/gills and (iii) muscle tissue were prepared and added to tanks holding the fry. Virus transmission occurred from all tissues tested, causing high mortality of the fry. The results underline the potential risk of introduction of VHSV through the trade of fish products.

Market-sized rainbow trout Oncorhynchus mykiss were challenged by waterborne exposure to viral haemorrhagic septicaemia virus (VHSV isolate of genogroup Ia). Fish were sampled at 4 stages of infection (before onset of clinical signs, clinically affected fish, mortalities and survivors) and the viral load determined in (1) internal organs, (2) muscle tissue and (3) brain and gill tissue. Virus levels were determined by virus titration and real-time RT-PCR. VHSV was detected by either method in the majority of fish before onset of clinical signs and in the survivor group as well as in all fish in the clinically affected fish and mortality groups. Mean virus amounts per mg of tissue determined by virus titration (TCID50) or real-time RT-PCR (copy number) were > 10(4) in preclinical fish, > 10(3.8) in clinically affected fish, > 10(3.9) in mortalities and > 10(1.2) in survivors. Virus levels tended to be highest in the internal organs of subclinical and clinically affected fish and in brain and gill tissue of survivors. The results demonstrate that significant levels of VHSV can be found in tissues of rainbow trout that may be marketed for human consumption, which may have relevance for the biosecurity of VHS-free areas.

This study investigated the use of alkaline hydrolysis at ambient temperature for inactivation of selected fish pathogens in fish tissues under conditions approximating those that are likely to be found in the aquaculture industry. Infectious salmon anaemia virus (ISAV) and Lactococcus garvieae have been determined in a previous study to be the most resistant virus and bacteria to pH 12 from a wide range of viruses and bacteria tested. They were spiked at high titres into fish extracts that were then treated with 1 m sodium hydroxide (NaOH). Viable L. garvieae was not detected in the treated fish extract after 1 h, and ISAV was not detected after 24-h exposure. Field mortalities of Atlantic salmon, Salmo salar L., caused by infectious pancreatic necrosis virus were treated by alkaline hydrolysis at ambient temperature. The macerated fish mortalities contained a high titre of virus (3.38 × 10⁸ TCID₅₀ g⁻¹) that was reduced to approximately 2.2 × 10³ TCID₅₀ g⁻¹ after 24-h exposure to NaOH, and virus was not detected after exposure for 48 h. The results suggest that alkaline hydrolysis at ambient temperature has potential as a biosecure treatment method for fish by-products containing fish pathogens.

Koi herpesvirus (KHV) causes a highly virulent disease affecting carp, Cyprinus carpio L., and poses a serious socio-economic threat to the UK carp industry. This study aimed to determine the geographic distribution and prevalence of KHV exposed fish in England and Wales through ELISA antibody testing. Only three of the 82 farms sampled produced positive results, suggesting fish farms provide a relatively safe source of fish. Of the 71 'high-risk' fisheries tested, 26 were positive. All eight geographic areas within England and Wales studied had at least one KHV positive site. Twelve consignments of imported koi carp from seven S.E. Asian countries were tested for KHV antibody. Six consignments from six different countries were positive. Although a high proportion of consignments were positive, the results indicate that lower risk stocks of fish exist that could be sourced by the ornamental carp sector. The study provides evidence that KHV is widespread and prevalent in 'high-risk' fisheries. There are, however, prospects for controlling KHV as English and Welsh farms appear to be relatively free of the virus, and in most cases fish are not moved from fisheries to other waters.

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Estimates of strain effects, heritabilities and genetic correlations for pond survival, resistance to Aeromonas hydrophila and resistance to koi herpesvirus (KHV) were obtained from a diallel cross of 92 full-sib families of common carp produced from four strains (Szarvas 15, Tata, Duna and Amur) and using five females and ten males per strain. Disease resistance was obtained from survival data from challenge-tests using intraperitoneal injection for A hydrophila and cohabitation for KHV. Two separate challenge-tests were conducted for each disease. The overall survival rates were 44% and 34% for the two tests of A. hydrophila, and 7% and 5% for the two tests of KHV. Pond survival (averaging 78%) was observed over a six months period prior to harvest (at approximately 18 months of age). The three traits were analysed jointly in a multivariate threshold model. For KHV the strain Szarvas 15 had the lowest observed (purebred) survival (0%) followed by Amur (11%), Duna (12%) and Tata (21%), while for A hydrophila, the lowest (purebred) survival was observed for Duna (28%) followed by Amur (31%), Szarvas 15 (38%) and Tata (48%). Heterosis was not significant for KHV and A. hydrophila resistance, although highly significant for pond survival. The estimated heritability (on the underlying liability scale) was low (0.04 +/- 0.03) for A. hydrophila resistance, very high (0.79 +/- 0.15) for KHV resistance, and moderate (0.34 +/- 0.09) for pond survival. The genetic correlation between the two challenge-tested diseases (KHV and A. hydrophila) was moderately high (0.61 +/- 0.29), although uncertain, while the estimated genetic correlations between pond survival and the two challenge-tested diseases were low and not significantly different from zero (0.01 +/- 0.28 and -0.22 +/- 0.21 for A. hydrophila and KHV, respectively). The latter may be expected for KHV, as no outbreaks of the disease had been observed in Hungary. Based on the favourable heritabilities of KHV and pond survival there is good prospect for joint improvement of these two traits in common carps through genetic selection. (C) 2010 Elsevier B.V. All rights reserved.

There is a need for standardised comparative data on the efficacy of aquaculture disinfectants to guide their use by farmers and health professionals, as well as Competent Authorities for authorisation or listing purposes. Towards this aim, two already available CEN (Comité Européen de Normalisation) quantitative suspension test standards for the evaluation of bactericidal and virucidal activity of disinfectants and antiseptics for use in the veterinary field were modified by using agents and testing conditions representative of aquaculture conditions. For evaluating bactericidal activity, BS EN1656:2000 was modified to test disinfectant activity against Aeromonas salmonicida subsp. salmonicida (ATCC 14174), Yersinia ruckeri (ATCC 29473), Carnobacterium piscicola (ATCC 35586) and Lactococcus garvieae (NCIMB 702927) for a contact time of 30 min and temperature of 4 °C. Interfering substance was used as described for dirty conditions in the standard (10 g l−1 yeast extract plus 10 g l−1 bovine serum albumin solution).