Characterization of Vibrio Populations from Cultured European Seabass and the Surrounding Marine Environment with Emphasis on V. anguillarum

Vibrio species are widely distributed and can be potentially pathogenic to aquatic organisms. In this study, we isolated Vibrio spp. from environmental samples (seawater, sediment, and fish swabs) collected over a three-year period from a fish farm in Mali Ston Bay in the Adriatic Sea, Croatia, and assess their distribution. A total of 48 seawater samples and 12 sediment samples, as well as gill and skin swabs from 110 farmed European seabass, were analysed for the presence of Vibrio. Vibrio strains were identified to the species level by MALDI TOF MS. The analysis revealed that V. alginolyticus was the predominant species in European seabass, followed by V. anguillarum. V. alginolyticus was isolated from the sediments, along with V. gigantis and V. pomeroyi, while V. chagasii, V. cyclitrophicus, V. fortis, V. gigantis, V. harveyi, V. pelagius, and V. pomeroyi were isolated from seawater. V. anguillarum was isolated only twice during two different spring seasons, once from a diseased sea bass and the second time from a healthy sea bass. We analysed these two isolates and found that they differ both genetically and in terms of resistance to antibiotics. Our results confirm the seasonality of vibriosis incidence and the presence of the pathogenic V. anguillarum, which increases the risk of vibriosis.

Early detection of salmonid alphavirus in seawater from marine farm sites of Atlantic salmon Salmo salar

The traditional strategy for national surveillance of salmonid alphavirus (SAV) infection in Norwegian fish farms relies on a costly, time-consuming, and resource-demanding approach based on the monthly sampling of fish from all marine farms with salmonids. In order to develop an alternative surveillance method, a water filtration method was tested in parallel with the ongoing surveillance program at 7 Norwegian marine farm sites of Atlantic salmon Salmo salar L. with no current suspicion of SAV infection. During the period from May 2019 to January 2020, seawater samples were collected from the top layer water inside all net-pens at these 7 sites. The samples were concentrated for SAV by filtration through an MF-Millipore™ electronegative membrane filter, followed by rinsing with NucliSENS® Lysis Buffer, before RNA extraction and analysis by RT-qPCR. SAV was detected from seawater at an earlier stage compared to traditional sampling methods, at all sites where the fish tested positive for SAV. A significant negative relationship was observed at all sites between the SAV concentration found in seawater samples and the number of days until SAV was detected in the fish. This means that the fewer the SAV particles in the seawater, the more days it took until SAV was detected in the fish samples. Based on this, sampling of seawater every month for the surveillance of SAV has a great potential as an alternative method for early detection of SAV in Atlantic salmon farms.

Infectious Salmon Anemia Virus Shedding from Infected Atlantic Salmon (Salmo salar L.)-Application of a Droplet Digital PCR Assay for Virus Quantification in Seawater

Infectious salmon anemia virus (ISAV) infection is currently detected by fish sampling for PCR and immunohistochemistry analysis. As an alternative to sampling fish, we evaluated two different membrane filters in combination with four buffers for elution, concentration, and detection of ISAV in seawater, during a bath challenge of Atlantic salmon (Salmo salar L.) post-smolts with high and low concentrations of ISAV. Transmission of ISAV in the bath challenge was confirmed by a high mortality, clinical signs associated with ISA disease, and detection of ISAV RNA in organ tissues and seawater samples. The electronegatively charged filter, combined with lysis buffer, gave significantly higher ISAV RNA detection by droplet digital PCR from seawater (5.6 × 10⁴ ISAV RNA copies/L; p < 0.001). Viral shedding in seawater was first detected at two days post-challenge and peaked on day 11 post-challenge, one day before mortalities started in fish challenged with high dose ISAV, demonstrating that a large viral shedding event occurs before death. These data provide important information for ISAV shedding that is relevant for the development of improved surveillance tools based on water samples, transmission models, and management of ISA.

Filtration, concentration and detection of salmonid alphavirus in seawater during a post-smolt salmon (Salmo salar) cohabitant challenge

Currently, the prevalence of salmonid alphavirus (SAV) in Norwegian Atlantic salmon farms is largely surveyed via sacrificing fish and sampling of organ tissue on a monthly basis. However, a more cost-efficient, straightforward, rapid, reliable, reproducible and animal welfare friendly method based on the detection of SAV in water could be considered as an alternative method. In the present study, such a method was developed and optimized through a 6 wk cohabitant challenge trial, using post-smolt Atlantic salmon Salmo salar L challenged with high or low doses of SAV subtype 3 (SAV3). Tank water and tissue samples from cohabitant fish were collected at 16 time points. SAV3 was concentrated from the water by filtration, using either electronegative or electropositive membrane filters, which were subsequently rinsed with one of 4 different buffer solutions. SAV3 was detected first in tank water (7 d post-challenge, DPC), and later in cohabitant fish organ tissue samples (12 DPC). The electronegative filter (MF-Millipore™) and rinsing with NucliSENS® easyMAG® Lysis Buffer presented the best SAV3 recovery. A significant positive correlation was found between SAV3 in the tank water concentrates and the mid-kidney samples. Based on these results, detection of SAV3 in filtrated seawater is believed to have the potential to serve as an alternative method for surveillance of SAV in Atlantic salmon farms.

Development and evaluation of a method for concentration and detection of salmonid alphavirus from seawater

Waterborne viral infections represent a major threat to fish health. For many viruses, understanding the interplay between pathogens, host and environment presents a major hurdle for transmission. Salmonid alphavirus (SAV) can infect and cause pancreas disease (PD) in farmed salmonids in seawater. During infection, SAV is excreted from infected fish to the seawater. We evaluated two types of filters and four different eluents, for concentration of SAV3. One L of seawater was spiked with SAV3, followed by filtration and virus elution from membrane filters. For the negatively charged MF hydrophilic membrane filter (MF-) combined with NucliSENS® lysis buffer the SAV3 recovery was 39.5 ± 1.8 % by RT-ddPCR and 25.9 ± 5.7 % by RT-qPCR. The recovery using the positively charged 1 MDS Zeta Plus® Virosorb® membrane filter (MD+), combined with NucliSENS® lysis buffer was 19.0 ± 0.1 % by RT-ddPCR and 13.3 ± 3.8 % by RT-qPCR. The limits of quantification (LOQ) and detection (LOD) were estimated to be 5.18 × 10³ and 2.0 × 10² SAV3 copies/L of natural seawater, by RT-ddPCR. SAV3 recovery from small volumes of seawater, and the requirement for standard laboratory equipment, suggest the MF-filter combined with NucliSENS® lysis buffer would be a candidate for further validation in experimental trials.

Infectious Salmon Anemia and Farm-Level Culling Strategies

Infectious salmon anemia (ISA) is an infectious disease, and outbreaks must be handled to avoid spread between salmon sea farms. Intensive culling at infected farms is an important biosecurity measure to avoid further spread but is also a costly intervention that farmers try to avoid. A lack of action, however, may lead to new outbreaks in nearby salmon sea farms, with severe impacts on both economy and animal welfare. Here, we aim to explore how a time delay between a detected outbreak and the culling of both infected cages and entire farms affects the further spread of the disease. We use a previously published model to calculate how many salmon sea farms were directly infected in each outbreak. To investigate the effect of culling on the further spread of disease, we use the number of months elapsed from the detected outbreak to (a) the first cage being depopulated, and (b) to the entire salmon sea farm being depopulated as predictors of how many new farms the virus was transmitted to, after controlling for contact between the farms. We show that the lapse in time before the first cage is depopulated correlates positively with how many new salmon sea farms are infected, indicating that infected cages should be culled with as little time delay as possible. The model does not have sufficient power to separate between culling of only cages assumed to be infected and the entire farm, and, consequently, provides no direct empirical evidence for the latter. Lack of evidence is not evidence, however, and we argue that a high probability of spread between cages in infected salmon sea farms still supports the depopulation of entire farms as the safest option.

Evaluation of aquaculture management zones as a control measure for salmon lice in Norway

We evaluated the use of coordinated fallowing as a means to control salmon lice Lepeophtheirus salmonis infestation in farmed Atlantic salmon Salmo salar. In discrete management zones, aquaculture operations such as stocking, fallowing, treatments and harvesting are synchronized at all sites in coordinated areas within the zones. The expected benefit of synchronized generations is to reduce the presence of salmon lice larvae after a period of fallowing, as well as to minimize external infestation pressure from surrounding aquaculture sites. A regression analysis was used to evaluate the effectiveness of coordinated fallowing on the progression of external salmon lice infestation pressure and abundance in Atlantic salmon farming sites in 2 areas (zones) in Norway. The overall results show that external infestation pressure was higher inside than outside the management zones, and the external infestation pressure increased with increasing biomass throughout the production cycle. However, within the zones, the external infestation pressure at the beginning of a production cycle was high and in many cases even higher than the general external infestation pressure in the non-coordinated areas. This suggests that external infestation pressure from the neighboring areas has a considerable effect on the fallowed area. Higher numbers of salmon lice were recorded within the zones than outside and, as the production cycle progressed, this phenomenon became more evident. We conclude that the high infestation pressure from salmon lice at the beginning of the grow-out period after fallowing raises severe doubts about the effectiveness of coordinated fallowing practices.

A pharmaco-epidemiological study of antibacterial treatments and bacterial diseases in Norwegian aquaculture from 2011 to 2016

The sales and prescription of antibacterials for use in Norwegian fish-farming according to diagnosis, fish species and production stage from 2011 to 2016 are analysed. The study is based on antibacterial sales data from wholesalers, pharmacies and feed mills and on prescription data obtained from a register of all prescriptions of antibacterials used in farmed fish. The results show that the fish-farming industry uses very small volumes of antibacterials. In 2016, a total of 212 kg were sold; the only antibacterial substances sold were florfenicol and oxolinic acid. The total amount corresponded to 0.16 mg kg-1 fish slaughtered, or to approximately 0.14% of the fish produced that year. The majority of prescriptions were for non-specific bacterial infections; as most common diseases are under control by vaccination. Most prescriptions for salmonid fish were during early production stages. However, due to higher biomasses of fish, the highest quantities of antibacterials were prescribed during the seawater production phase of Atlantic salmon Salmo salar. An increasing proportion of the prescriptions was for other species, including cleaner fish used for salmon lice control; in 2016 most prescriptions were for this fish category. Due to the negligible use of antibacterials in Norwegian aquaculture, in particular for on-growers, the risk of development of antimicrobial resistance and its transmission to humans through consumption of fish is considered negligible.

The epidemiology of pancreas disease in salmonid aquaculture: a summary of the current state of knowledge

Pancreas disease (PD) is a viral disease caused by Salmonid alphavirus (SAV) that affects farmed Atlantic salmon (Salmo salar L.) and rainbow trout (Oncorhynchus mykiss (Walbaum)) in the seawater phase. Since its first description in Scotland in 1976, a large number of studies have been conducted relating to the disease itself and to factors contributing to agent spread and disease occurrence. This paper summarizes the currently available, scientific information on the epidemiology of PD and its associated mitigation and control measures. Available literature shows infected farmed salmonids to be the main reservoir of SAV. Transmission between seawater sites occurs mainly passively by water currents or actively through human activity coupled with inadequate biosecurity measures. All available information suggests that the current fallowing procedures are adequate to prevent agent survival within the environment through the fallowing period and thus that a repeated disease outbreak at the same site is due to a new agent introduction. There has been no scientific evaluation of currently used on-site biosecurity measures, and there is limited information on the impact of available mitigation measures and control strategies.

Genetic characterization of salmonid alphavirus in Norway

Pancreas disease (PD), caused by salmonid alphavirus subtype 3 (SAV3), emerged in Norwegian aquaculture in the 1980s and is now endemic along the south-western coast. In 2011, the first cases of PD caused by marine salmonid alphavirus subtype 2 (SAV2) were reported. This subtype has spread rapidly among the fish farms outside the PD-endemic zone and is responsible for disease outbreaks at an increasing numbers of sites. To describe the geographical distribution of salmonid alphavirus (SAV), and to assess the time and site of introduction of marine SAV2 to Norway, an extensive genetic characterization including more than 200 SAV-positive samples from 157 Norwegian marine production sites collected from May 2007 to December 2012 was executed. The first samples positive for marine SAV2 originated from Romsdal, in June 2010. Sequence analysis of the E2 gene revealed that all marine SAV2 included in this study were nearly identical, suggesting a single introduction into Norwegian aquaculture. Further, this study provides evidence of a separate geographical distribution of two subtypes in Norway. SAV3 is present in south-western Norway, and marine SAV2 circulates in north-western and Mid-Norway, a geographical area which since 2010 constitutes the endemic zone for marine SAV2.

Ixodes ricinus infestation in free-ranging cervids in Norway--a study based upon ear examinations of hunted animals

Prevalence, abundance and instar composition of Ixodes ricinus as found on one ear collected from 1019 moose (Alces alces), red deer (Cervus elaphus) and roe deer (Capreolus capreolus), shot during hunting (August-December) 2001-2003, are reported. The animals originated from 15 coastal municipalities (CM), seven municipalities bordering to coastal municipalities (BCM) and four inland municipalities (IM), in Norway, between latitudes 58-66° N. I. ricinus occurred endemically in all CM and BCM up to 63°30' N, whereas it was non-endemic further north and in the IM. This geographical distribution of the tick along the coast of southern Norway was largely in accordance with that reported as far back as the 1940s. Our results therefore did not indicate any large scale northwards expansion of I. ricinus in Norway during the 60 year-period between the two studies. However, the prevalence of infestation and tick abundance were significantly higher in CM as compared to BCM. The prevalence and abundance by month were highest during August and September, gradually decreasing towards December. The considerable prevalence of ticks in November, as well as findings in December, would seem to indicate a prolonged tick season as compared with the studies carried out 60 years ago. A total of 8920 ticks were isolated from 439 of the 603 animals examined in endemic municipalities, and the maximum number of ticks found on one single ear was 204. Attached adult ticks were primarily found among the long hairs at base of the ear, whereas nymphs and larvae were seen all over the outer surface of the pinna, for larvae especially at the edge and tip of the ear. Nymphs were the dominant instar, constituting 74% of the total tick count. The proportion of larvae and adult ticks was 13% and 12%. A significantly higher proportion of adult ticks and lower proportion of immature stages were found in moose, as compared to red deer and roe deer. The same apparently size-associated preference of adult ticks was also found for adult animals (all species) as compared to calves. Other grossly detected ectoparasites included the lice Solenopotes burmeisteri in red deer and Damalinia meyeri in roe deer, and the deer ked fly, Lipoptena cervi, in moose and roe deer. This is believed to be the first systematic study on the instar composition by I. ricinus infestation in free-ranging cervids. The examination of ears from hunted cervids should be recognized as a rational way of obtaining data on the geographical distribution and abundance of this tick in nature.

National biosecurity approaches, plans and programmes in response to diseases in farmed aquatic animals: evolution, effectiveness and the way forward

The rapid increase in aquaculture production and trade, and increased attention to the negative effects of disease, are becoming stimuli for developing national biosecurity strategies for farmed fisheries, for which the World Organisation for Animal Health (OIE) Aquatic Animal Health Code and Manual of Diagnostic Tests for Aquatic Animals serve as an excellent framework. Using examples from a few countries and selected diseases, this paper provides a general overview of the development of approaches to implementing biosecurity strategies, including those emerging in the national legislation and regulations of some countries, and those being initiated by industries themselves. The determination of disease status in different epidemiological units (from a farm to a nation), appropriate approaches for preventing the introduction of disease and developing contingencies for disease control and eradication are also discussed. Important to the effectiveness of such strategies are provision of financial, personnel and other resources to implement them, including incentives such as indemnification or compensation in eradication programmes, and practical linkage to regulatory or government policy initiatives.

A severe outbreak of contagious ecthyma (orf) in a free-ranging musk ox (Ovibos moschatus) population in Norway

During July-October 2004, 19 (18 calves, 1 yearling) free-ranging musk oxen (Ovibos moschatus) at Dovre, Norway, were observed with contagious echtyma-like lesions, and 16 of them were euthanized. Six musk oxen were subjected to necropsy, histopathological and microbiological examinations. All euthanized animals had lesions consistent with contagious ecthyma presenting as wart-like, scabby lesions on the muzzle, lips, oral mucosa and limbs to a variable extent. The histopathological examination showed pustular dermatitis characterized by epidermal proliferation, reticular degeneration, degenerating keratinocytes with intracytoplasmic eosinophilic inclusion bodies, vesicopustules, microabscesses and multifocal ulcerations in the epidermis which was covered by a serocellular crust. Pathology and bacteriology showed evidence of secondary infections in the skin and draining lymph nodes. Electron microscopy (negative staining) of lesions from four animals detected parapoxvirus with the typical arrangement of the outer protein filaments. Parapoxvirus DNA was detected in tissue samples from two examined animals by polymerase chain reaction (PCR) with primers from the B2L-gene. A DNA sequence of 326 nucleotides from the amplicon was compared with similar DNA sequences from parapoxvirus isolated from sheep, reindeer, musk ox and cattle. The outbreak was caused by a virus similar to other circulating orf virus variants in Norway. Antibodies against parapoxvirus were detected with a virus neutralization test in 3 of 35 musk oxen (8.6%) sampled at Dovre between 2004 and 2006. This is the first report of a severe outbreak of contagious ecthyma in free-ranging musk oxen.

Malignant catarrhal fever in free-ranging cervids associated with OvHV-2 and CpHV-2 DNA

Pathologic lesions were summarized in 18 free-ranging cervids (15 moose [Alces alces], two roe deer [Capreolus capreolus], and one red deer [Cervus elaphus]) diagnosed with malignant catarrhal fever (MCF) after examination at the National Veterinary Institute, Oslo 1982-2005. Eye lesions (conjunctivitis, corneal opacity, fibrin clots in the anterior eye chamber) were the most frequent gross finding. Erosive-ulcerative mucosal lesions in the nose and mouth were also commonly found. Histopathology revealed a nonpurulent vasculitis and perivasculitis in the central nervous system (CNS) typical of MCF in 16 of the cases. The diagnosis in the remaining two animals was based upon histologic eye lesions consistent with MCF (CNS not available for examination). Polymerase chain reaction was run on samples from 15 individuals for evidence of MCF-virus DNA, and ovine herpesvirus-2 (OvHV-2) DNA was detected in five moose, one roe deer, and one red deer, and caprine herpesvirus-2 (CpHV-2) DNA was detected in two moose and one roe deer. Sera from 1,000 free-ranging cervids were tested for specific antibodies to MCF-associated viruses (MCFV) by competitive inhibition enzyme-linked immunosorbent assay. The seroprevalences were: red deer 5%, reindeer (Rangifer tarandus) 4%, roe deer 2%, and moose 0.4% (n = 250 for all four species). The results indicate that sheep and goat MCFV may cause serious disease in wild moose, roe deer, and red deer. The seropositive cervids most likely represent individuals infected with either OvHV-2 or CpHV-2, but may also reflect infections with other related MCFV.

A new system for monitoring health status in Norwegian aquaculture

In Norway there is an official system (ANISTAT) for reporting notifiable diseases to the Norwegian Food Safety Authority, which is mainly done by veterinarians and laboratories. Another separate official system (HAVBRUKSDATA) is also in place, for reporting production data from fish farms, such as the number of fish put into the sea, and their weight, density, feed consumption and mortality. The reported data are aggregated monthly with information from companies' private databases related to each production site and each production unit. There also are official procedures in place for the registration of drugs used in aquaculture, based on veterinary prescriptions. However there is no electronic system for active reporting diseases influencing production and/or welfare. It is our aim to establish a more advanced official system for monitoring the health situation in Norwegian fish farms (MFISK) by linking relevant production data from the various private databases to an official disease database. The output of the new system will be improved statistics on diseases in the Norwegian fish farming industry, with diseases sorted by their impact on production and welfare. This will enable us to identify diseases that, over time, cause such losses that they should be dealt with by the authorities, or by the farmers themselves. It will also have an early warning function regarding new/emerging diseases or disease trends. This system quantifies losses due to health problems and, in the long run, will be a useful tool for strengthening fish health. The system aims to combine data from various sources: the veterinary and fisheries authorities in Norway, farmers, veterinarians and laboratories. To be sustainable, it will need the active and constructive cooperation of all these stakeholders.

Food safety hazards that occur during the production stage: challenges for fish farming and the fishing industry

Seafood derived from wild fish as well as farmed fish has always been an important source of protein in the human diet. On a global scale, fish and fish products are the most important source of protein and it is estimated that more than 30% of fish for human consumption comes from aquaculture. The first part of this paper outlines the hazards and challenges associated with handling fish during farming and capture. The authors describe infectious agents that cause disease in fish as well as humans, zoonotic agents, intoxications due to bacteria and allergies caused by the consumption of fish. Although only a few infectious agents in fish are able to infect humans, some exceptions exist that may result in fatalities. However, the greatest risk to human health is due to the consumption of raw or insufficiently processed fish and fish products. The second part of the paper considers environmental contaminants in seafood that may pose a risk to human health, such as medicinal products and residues associated with aquaculture, persistent lipophilic organic compounds and metals (methyl-mercury, organotin). The authors include an updated overview of the various factors associated with farmed and captured fish that may cause risks to human health after consumption. Moreover, they discuss the challenges (in the widest sense) associated with handling fish during capture and farming, as well as those encountered during processing.

Screening of feral pigeon (Colomba livia), mallard (Anas platyrhynchos) and graylag goose (Anser anser) populations for Campylobacter spp., Salmonella spp., avian influenza virus and avian paramyxovirus

A total of 119 fresh faecal samples were collected from graylag geese migrating northwards in April. Also, cloacal swabs were taken from 100 carcasses of graylag geese shot during the hunting season in August. In addition, samples were taken from 200 feral pigeons and five mallards. The cultivation of bacteria detected Campylobacter jejuni jejuni in six of the pigeons, and in one of the mallards. Salmonella diarizona 14:k:z53 was detected in one graylag goose, while all pigeons and mallards were negative for salmonellae. No avian paramyxovirus was found in any of the samples tested. One mallard, from an Oslo river, was influenza A virus positive, confirmed by RT-PCR and by inoculation of embryonated eggs. The isolate termed A/Duck/Norway/1/03 was found to be of H3N8 type based on sequence analyses of the hemagglutinin and neuraminidase segments, and serological tests. This is the first time an avian influenza virus has been isolated in Norway. The study demonstrates that the wild bird species examined may constitute a reservoir for important bird pathogens and zoonotic agents in Norway.

Prevalence of Trichinella larvae and extra-intestinal nematodes in Norwegian red foxes (Vulpes vulpes)

A survey of the parasitic fauna of the Norwegian red fox (Vulpes vulpes) population was carried out in 1994/1995 and 2002-2005. All foxes were killed during the licensed hunting season from October to April and, in total, 393 animals from all regions of the country were examined. The present study details the results of extra-intestinal nematode and Trichinella larvae examinations. All individuals were examined for Trichinella, using routine digestion methods. Parasitological examination of the internal organs of some of the foxes also identified a number of different extra-intestinal nematodes. The following prevalences were identified (number positive/number foxes examined): Trichinella larvae 19/393 (4.8%); Capillaria böhmi (C. böhmi) 88/174 (51%); Capillaria aerophila (C. aerophila) 160/181 (88%); Crenosoma vulpis (Cr. vulpis) 105/181 (58%) and Capillaria plica (C. plica) 81/154 (53%). No evidence of Angiostrongylus vasorum infection was found. The 19 different Trichinella isolates were species typed by PCR and sequence analysis; 18 isolates were identified as Trichinella nativa and one as Trichinella britovi. A wide geographical distribution of the parasites was seen. The following exceptions were recorded: C. böhmi, the prevalence of which was significantly lower in northern Norway (6%) compared to other regions (central Norway, eastern Norway and southern and western Norway; 52-57%). There was a significantly higher prevalence of Trichinella infection in eastern Norway (8.1%), when compared with the rest of the country (0.6%). Cr. vulpis prevalence was significantly higher in central Norway (83%) than in other regions (41-56%). There were no significant differences in age and sex distribution of the parasites with the exception of Cr. vulpis where juvenile foxes had a greater likelihood of infection. The data also indicated that adult foxes were more commonly infected with Trichinella larvae (5.8%) than juveniles (3.3%) (no statistical significance).

Molecular identification and characterization of novel coronaviruses infecting graylag geese (Anser anser), feral pigeons (Columbia livia) and mallards (Anas platyrhynchos)

In light of the finding of a previously unknown coronavirus as the aetiology of the severe acute respiratory syndrome (SARS), it is probable that other coronaviruses, than those recognized to date, are circulating in animal populations. Here, the results of a screening for coronavirus are presented, using a universal coronavirus RT-PCR, of the bird species graylag goose (Anser anser), feral pigeon (Columbia livia) and mallard (Anas platyrhynchos). Coronaviruses were found in cloacal swab samples from all the three bird species. In the graylag goose, 40 of 163 sampled birds were coronavirus positive, whereas two of 100 sampled pigeons and one of five sampled mallards tested positive. The infected graylag geese showed lower body weights compared with virus-negative birds, suggesting clinical significance of the infection. Phylogenetic analyses performed on the replicase gene and nucleocapsid protein sequences, indicated that the novel coronaviruses described in the present study all branch off from group III coronaviruses. All the novel avian coronaviruses harboured the conserved s2m RNA structure in their 3′ untranslated region, like other previously described group III coronaviruses, and like the SARS coronavirus. Sequencing of the complete nucleocapsid gene and downstream regions of goose and pigeon coronaviruses, evidenced the presence of two additional open reading frames for the goose coronavirus with no sequence similarity to known proteins, but with predicted transmembrane domains for one of the encoded proteins, and one additional open reading frame for the pigeon coronavirus, with a predicted transmembrane domain, downstream of the nucleocapsid gene.

Campylobacter spp., Salmonella spp., verocytotoxic Escherichia coli, and antibiotic resistance in indicator organisms in wild cervids

Faecal samples were collected, as part of the National Health Surveillance Program for Cervids (HOP) in Norway, from wild red deer, roe deer, moose and reindeer during ordinary hunting seasons from 2001 to 2003. Samples from a total of 618 animals were examined for verocytotoxic E. coli (VTEC); 611 animals for Salmonella and 324 animals for Campylobacter. A total of 50 samples were cultivated from each cervid species in order to isolate the indicator bacterial species E. coli and Enterococcus faecalis / E. faecium for antibiotic resistance pattern studies. Salmonella and the potentially human pathogenic verocytotoxic E. coli were not isolated, while Campylobacter jejuni jejuni was found in one roe deer sample only. Antibiotic resistance was found in 13 (7.3%) of the 179 E. coli isolates tested, eight of these being resistant against one type of antibiotic only. The proportion of resistant E. coli isolates was higher in wild reindeer (24%) than in the other cervids (2.2%). E. faecalis or E. faecium were isolated from 19 of the samples, none of these being reindeer. All the strains isolated were resistant against one (84%) or more (16%) antibiotics. A total of 14 E. faecalis-strains were resistant to virginiamycin only. The results indicate that the cervid species studied do not constitute an important infectious reservoir for either the human pathogens or the antibiotic resistant microorganisms included in the study.

Prevalence of Vancomycin Resistant Enterococci on Poultry Farms Established After the Ban of Avoparcin

Fecal samples from poultry on farms established after the ban of avoparcin (study farms) and from poultry on farms previously exposed to avoparcin (control farms) were examined for the presence of vancomycin-resistant enterococci (VRE). The samples were collected during the autumn and winter of 2001-2002. One isolate from each positive sample was selected, identified to species level, and examined for the presence of the vanA gene. The concentration of VRE and generic enterococci in the samples were also determined. In addition, the susceptibility to the ionophoric coccidiostat narasin was examined in a number of enterococcal isolates from poultry and in some enterococci of porcine origin that had not been exposed to narasin. VanA-type VRE was detected in samples from 64% of the study farms and 96% of the control farms. However, the concentration of VRE in the control samples was about six times larger than in the samples from the study farms. The minimum inhibitory concentration values for narasin differed between the poultry (1-4 mg/liter) and the porcine (0.25-0.5 mg/liter) isolates, indicating a decreased susceptibility towards narasin among enterococci from poultry.

Antibodies to ruminant alpha-herpesviruses and pestiviruses in Norwegian cervids

A serologic survey revealed that Norwegian populations of free-ranging reindeer (Rangifer tarandus tarandus), roe deer (Capreolus capreolus), red deer (Cervus elaphus), and moose (Alces alces) have been exposed to alpha-herpesviruses and pestiviruses. A total of 3,796 serum samples collected during the period 1993-2000 were tested in a neutralization test for antibodies against bovine herpesvirus 1 (BHV-1) or cervid herpesvirus 2 (CerHV-2), and 3,897 samples were tested by a neutralization test and/or enzyme-linked immunosorbent assay for antibodies against bovine viral diarrhea virus (BVDV). Antibodies against alpha-herpesvirus were found in 28.5% of reindeer, 3.0% of roe deer, and 0.5% of red deer, while all moose samples were negative. In reindeer, the prevalence of seropositive animals increased with age and was higher in males than females. Antibodies against BVDV were detected in 12.3% of roe deer, 4.2% of reindeer, 2.0% of moose and 1.1% of red deer. The results indicate that both alpha-herpesvirus and pestivirus are endemic in reindeer and pestivirus is endemic in roe deer in Norway. The viruses may be specific cervid strains. Seropositive red deer and moose may have become exposed as a result of contact with other ruminant species.

Maternal vaccination against subclinical necrotic enteritis in broilers

The inclusion of antibacterial feed additives has until now been the major strategy for controlling Clostridium perfringens-associated necrotic enteritis in broilers. In the present study, the effect of maternal immunization against the disease was examined. Broiler breeder hens were injected intramuscularly with candidate vaccines based on C. perfringens type A and type C toxoids adjuvanted with aluminium hydroxide. Vaccination resulted in a strong serum immunoglobulin G response to C. perfringens alpha-toxin in parent hens, and specific antibodies were transferred to their progeny. Subclinical necrotic enteritis in broilers was induced under field conditions or in a disease model, and the occurrence of specific enteric and hepatic lesions was evaluated in randomly selected birds. In three experiments, estimates of odds ratio for developing such lesions were 0.23, 0.33 and 0.56 in maternally toxoid C-immunized broilers compared with non-immunized controls. In toxoid A-immunized birds, odds ratios were estimated at 0.41, 0.61 and 0.63. From these results, immunoprophylaxis seems to be an interesting alternative for the control of necrotic enteritis in broilers.

Epidemiology of bacterial diseases in Norwegian aquaculture--a description based on antibiotic prescription data for the ten-year period 1991 to 2000

In Norway, antibacterial drugs for use in farmed fishes have to be prescribed by a veterinarian. Moreover, a national surveillance programme requires that copies of all prescriptions be sent to the Directorate of Fisheries. The prescriptions give information regarding fish farm and locality, weight and species of fish to be medicated, diagnosis, type and amount of drug prescribed, and date. These prescription data for the 10 yr period 1991 to 2000 have been recorded and systematised. A total of 6322 prescriptions issued for 11 fish species were registered; Atlantic salmon represented 87% of the prescriptions, rainbow trout 4.5%, arctic char 0.3%, turbot 3.8%, halibut 2.1%, Atlantic cod 1.2%, and European eel 0.3%. European sea-bass, wolf-fish, coalfish and wrasse represented a total of 0.4% of the prescriptions. Furunculosis was the most frequently given diagnosis in Atlantic salmon, accounting for 79% of all prescriptions for this species. Furunculosis was more frequent during the summer and early autumn, and in the western parts of Norway. Fish weighing more than 1 kg seemed to be the most susceptible. However, furunculosis has almost disappeared in Norwegian aquaculture since 1993. Vibriosis gave cause for antibiotic treatments in almost all fish species, and was the most common diagnosis in rainbow trout, halibut, turbot, cod and European eel. In Atlantic salmon, fish of small and medium size (up to 1 kg) seemed to be more at risk from vibriosis, and outbreaks were more frequent during summer, and in the western counties. Cold-water vibriosis was the second most frequently treated disease in Atlantic salmon, creating severe problems mainly in larger fish, in the northern parts of the country, and during winter and spring. The seasonal distribution was similar for winter ulcer disease, the only disease which seemed to be of increasing importance in Atlantic salmon. Non-specific diagnoses, such as 'bacterial infection' and 'fry disease', were given in a much higher proportion of prescriptions for marine fish species than in prescriptions for salmonids.

Prudent use of antibacterial drugs in Norwegian aquaculture? Surveillance by the use of prescription data

Antibacterial drug treatment in aquaculture during 1991-1996 was investigated using prescription data provided by the Norwegian Government Fish Inspection and Quality Control Service (NFCS). The majority of prescriptions (n = 5401) were for Atlantic salmon and rainbow trout (salmonids), while 383 prescriptions were for other species. Of the 13 different single substances or combinations prescribed during the study period, only 5 were approved for or had been subjected to clinical trials in salmonids. Of the prescriptions for the salmonids, 99% were for approved drugs or drugs subjected to clinical trials. The major proportion of the antibacterial drugs prescribed for other fish species were drugs which were approved for or which had been subjected to clinical trials in salmonids. In all fish species, the prescribing of antibacterial drugs which were neither approved for nor had been subjected to clinical trials was mainly for fish far below slaughter weight. The prescription data were validated against the drug statistics from the wholesalers and feed mills. It was concluded that the data indeed represented antibacterial drug prescribing in Norwegian aquaculture. The prescribing of antibacterial drugs proved to be almost completely reported to NFCS, which is responsible for the control of drug residues in farmed fish in Norway.

Recent developments in fish vaccinology

During the last 10 to 20 years vaccination has become established as an important method for prevention of infectious diseases in farmed fish, mainly salmonid species. So far, most commercial vaccines have been inactivated vaccines administered by injection or immersion. Bacterial infections caused by Gram-negative bacteria such as Vibrio sp., Aeromonas sp., and Yersinia sp. have been effectively controlled by vaccination. With furunculosis, the success is attributed to the use of injectable vaccines containing adjuvants. Vaccines against virus infections, including infectious pancreatic necrosis, have also been used in commercial fish farming. Vaccines against several other bacterial and viral infections have been studied and found to be technically feasible. Pasteurellosis, streptococcosis (lactococcosis) and infections with iridoviruses are candidate diseases for control by immunoprophylaxis in the near future. The overall positive effect of vaccination in farmed fish is reduced mortality. However, for the future of the fish farming industry it is also important that vaccination contributes to a sustainable biological production with negligible consumption of antibiotics. A potential side-effect associated with injectable vaccines is local reactions in the peritoneal cavity. The paper presents recent developments in immunoprophylaxis of fish and some problems that should be addressed by the research community in the years to come.

Prudent use of antibacterial drugs in Norwegian aquaculture? Surveillance by the use of prescription data

Antibacterial drug treatment in aquaculture during 1991-1996 was investigated using prescription data provided by the Norwegian Government Fish Inspection and Quality Control Service (NFCS). The majority of prescriptions (n = 5401) were for Atlantic salmon and rainbow trout (salmonids), while 383 prescriptions were for other species. Of the 13 different single substances or combinations prescribed during the study period, only 5 were approved for or had been subjected to clinical trials in salmonids. Of the prescriptions for the salmonids, 99% were for approved drugs or drugs subjected to clinical trials. The major proportion of the antibacterial drugs prescribed for other fish species were drugs which were approved for or which had been subjected to clinical trials in salmonids. In all fish species, the prescribing of antibacterial drugs which were neither approved for nor had been subjected to clinical trials was mainly for fish far below slaughter weight. The prescription data were validated against the drug statistics from the wholesalers and feed mills. It was concluded that the data indeed represented antibacterial drug prescribing in Norwegian aquaculture. The prescribing of antibacterial drugs proved to be almost completely reported to NFCS, which is responsible for the control of drug residues in farmed fish in Norway.

Growth of Atlantic salmon Salmo salar after intraperitoneal administration of vaccines containing adjuvants

Growth of Atlantic salmon after intraperitoneal (i.p.) administration of adjuvanted vaccines was studied using groups of individually tagged fish held together in one tank or pen under commercial farming conditions. Parallel experiments were initiated at 2 freshwater sites and 1 marine site. Trivalent (vibriosis, cold water vibriosis and furunculosis) vaccines containing oil or beta-1, 3 glucan as adjuvants were used for immunisation of pre-smolts, whereas identical formulations containing furunculosis antigens only were used in growers. Control fish remained unvaccinated. No outbreak of bacterial or viral disease was experienced at any of the sites. At all sites, the highest daily growth rate was recorded in unvaccinated fish. At one site, the average weight of post-smolts that had received oil-adjuvant vaccine was significantly reduced by 345 g (23%) after 15 mo. Impaired growth rate was associated with increasing severity of intra-abdominal lesions as determined during necropsy. At the second post-smolt site and in growers, weight development and growth rates were non-significant between groups throughout the study. The results indicate that intraperitoneal administration of oil-adjuvanted vaccines may retard growth of farmed Atlantic salmon, although the extent of this effect may vary between sites. Unidentified factors coinciding with vaccination are thought to have caused the highly variable results seen between parallel sites in this study.

Vaccination strategies in seawater cage culture of salmonids

Successful vaccination depends both on the development of protective vaccines and their correct use. In addition to deciding which diseases to vaccinate against, the choice of the method, timing, and use of revaccination must be considered. In seawater culture of salmonids, vibriosis and furunculosis are the most important diseases against which to vaccinate in many parts of the world, while cold-water vibriosis is of great significance in Atlantic salmon in some areas with low water temperatures. A vaccine against infectious pancreatic necrosis (IPN) has also been introduced recently. For optimal protection of salmonids in sea-water, vaccination should be carried out some time before sea transfer, in order to give immunity sufficient time to develop, and to avoid handling stress during smoltification. On the other hand however, vaccination should not be carried out too early, as the degree of immunity declines with time. Water temperature is an important factor when deciding when to vaccinate. Recent research has demonstrated that Atlantic salmon may be vaccinated successfully at low water temperatures. In general, vaccination by the injection method gives superior protection. Vaccines against the Vibrio-infections can also be administered successfully by immersion. However, due to lower levels of immunity, the need for a booster vaccination is greater when such a method is used. As regards vaccines against furunculosis, adjuvants are needed in order to achieve good protection, and, consequently, administration by injection is the only option.

Vaccination in European salmonid aquaculture: a review of practices and prospects

Disease control by vaccination is widely used in European salmonid aquaculture against vibriosis (Vibrio anguillarum), cold-water vibriosis (Vibrio salmonicida), yersiniosis or enteric redmouth disease (Yersinia ruckeri) and furunculosis (Aeromonas salmonicida subsp. salmonicida). The vaccines against the Vibrio spp. and Y. ruckeri have proven effective especially when administered by injection. Furunculosis vaccines have been less successful and have relied on combination with potent adjuvants to achieve acceptable protection. Application of modern molecular techniques to furunculosis research has delivered a crop of experimental vaccines that incorporate purified virulence factors and have shown increased protection during challenge. Gene technology has also been used to create a defined, nonreverting mutation in a strain of A. salmonicida, which has enhanced the feasibility of attenuated live vaccines. The development of experimental subunit vaccines against the viral infections and the continued advances in the field of immunostimulants, adjuvants and antigen carriers provide considerable promise for the future development of commercial vaccines for use in salmonid aquaculture.

Characterization of Vibrio anguillarum and closely related species isolated from farmed fish in Norway

A total of 264 bacterial strains tentatively or definitely classified as Vibrio anguillarum were examined. The strains were isolated from diseased or healthy Norwegian fish after routine autopsy. With the exception of five isolates from wild saithe (Pollachius virens), the strains originated from nine different species of farmed fish. The bacteria were subjected to morphological, physiological, and biochemical studies, numerical taxonomical analyses, serotyping by slide agglutination and enzyme-linked immunosorbent assay, DNA-plasmid profiling, and in vitro antimicrobial drug susceptibility testing. The results of the microbiological studies were correlated to anamnestic information. The bacterial strains were identified as V. anguillarum serovar O1 (n = 132), serovar O2 (n = 89), serovar O4 (n = 2), serovar O8 (n = 1), and not typeable (n = 1) as well as Vibrio splendidus biovar I (n = 36) and biovar II (n = 1), Vibrio tubiashii (n = 1), and Vibrio fischerii (n = 1). V. anguillarum serovar O1 or O2 was isolated in 176 out of 179 cases of clinical vibriosis in Atlantic salmon (Salmo salar). V. anguillarum serovar O1 was the only serovar isolated from salmonid fish species other than Atlantic salmon, while V. anguillarum serovar O2 was isolated from all marine fish suffering from vibriosis. A 48-Mda plasmid was isolated from all V. anguillarum serovar O1 isolates examined. Serovar O2 isolates did not harbor any plasmids. Resistance against commonly used antibiotic compounds was not demonstrated among V. anguillarum isolates. Neither V. splendidus biovar I nor other V. anguillarum-related species appeared to be of clinical importance among salmonid fish.(ABSTRACT TRUNCATED AT 250 WORDS)