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.

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.

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.

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.

Short communication: Evaluation of charged membrane filters and buffers for concentration and recovery of infectious salmon anaemia virus in seawater.

Infectious salmon anaemia virus (ISAV) is the cause of an important waterborne disease of farmed Atlantic salmon. Detection of virus in water samples may constitute an alternative method to sacrificing fish for surveillance of fish populations for the presence of ISA-virus. We aimed to evaluate different membrane filters and buffers for concentration and recovery of ISAV in seawater, prior to molecular detection. One litre each of artificial and natural seawater was spiked with ISAV, followed by concentration with different filters and subsequent elution with different buffers. The negatively charged MF hydrophilic membrane filter, combined with NucliSENS® lysis buffer, presented the highest ISAV recovery percentages with 12.5 ± 1.3% by RT-qPCR and 31.7 ± 10.7% by RT-ddPCR. For the positively charged 1 MDS Zeta Plus® Virosorb® membrane filter, combined with NucliSENS® lysis buffer, the ISAV recovery percentages were 3.4 ± 0.1% by RT-qPCR and 10.8 ± 14.2% by RT-ddPCR. The limits of quantification (LOQ) were estimated to be 2.2 x 103 ISAV copies/L of natural seawater for both RT-qPCR and RT-ddPCR. The ISAV concentration method was more efficient in natural seawater.

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.

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 ±â€¯1.8 % by RT-ddPCR and 25.9 ±â€¯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 ±â€¯0.1 % by RT-ddPCR and 13.3 ±â€¯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.

Natural and experimental Salmonella Typhimurium infections in foxes (Vulpes vulpes).

The red fox (Vulpes vulpes) can be considered as a relevant indicator species for Salmonella in the local environment and Salmonella faecal carriage was investigated in 215 red foxes in Norway shot during the winters 2002/2003 and 2003/2004. Fourteen (6.5%) of the foxes carried Salmonella. Four isolates were determined as serovars Kottbus (n=2) and Hessarek (n=2) of Salmonella enterica subspecies enterica, and one as S. enterica subspecies IIIb:61:k:1,5,(7). The remaining nine isolates were S. enterica subspecies enterica serovar Typhimurium 4,12:i:1,2 and all displayed the same pulsed-field gel electrophoresis (PFGE) profile designated A2. This serovar regularly causes disease outbreaks amongst small passerine birds during winter and most of these outbreaks are associated with the PFGE profile A2. The results strongly indicated that the Salmonella Typhimurium infections in red foxes were primarily acquired through ingestion of infected small passerines. To investigate the capability of the A2 strain to establish a true intestinal infection in the fox an inoculation experiment with an A2 isolate from small passerines was carried out in farmed silver foxes (V. vulpes). The experiment also included one strain with an uncommonly occurring profile (X201) from small passerines. To highlight possible differences in capability of the two inoculation strains to pass the acid gastric juice in the fox, in vitro studies of their acid tolerance was carried out. Also their catalase activity and biofilm production were studied. All three foxes inoculated with the A2 strain developed sub-clinical intestinal infection of 2 weeks duration, whereas none of the three foxes inoculated with the X201 strain shed this bacterium. The X201 strain displayed a much lower capability, than the A2 strain, to survive at pH 3 in vitro. The low acid tolerance probably made it difficult for the X201 strain to pass the stomach and establish an intestinal infection in the experimental foxes. Reduced catalase activity and biofilm production were found for the X201 strain, indicating that the low acid tolerance was caused by a defect in the stationary-phase stress response system.

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.

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).

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.

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.

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.

Serosurvey for canine distemper virus, canine adenovirus, Leptospira interrogans, and Toxoplasma gondii in free-ranging canids in Scandinavia and Svalbard.

Prevalence of antibodies reactive to canine distemper virus (CDV), canine adenovirus type 1 (CAV-1), Leptospira interrogans serovars Canicola and Icterohaemorrhagiae, and Toxoplasma gondii were examined in free-ranging Scandinavian canids. Sampling included 275 red foxes (Vulpes vulpes) from mainland Norway, 60 arctic foxes (Vulpes lagopus) from the high-arctic islands of Svalbard, and 98 wolves (Canis lupus) from the joint Swedish-Norwegian population. Methods used included virus neutralization tests for CDV and CAV-1, a microscopic agglutination test for L. interrogans, and a direct agglutination test for T. gondii. High prevalence of antibody to CAV-1 was identified in red foxes (59.6%), wolves (67.7%), and arctic foxes (37.8%). The prevalence of antibody to CDV varied between 9.6% and 12.3% in the three species. Antibodies to L. interrogans serovar Icterohaemorrhagiae were found in 9.9% of the red foxes and 8.4% of the wolves sampled, whereas no antibody-positive arctic foxes were found. All animals were antibody-negative for L. interrogans serovar Canicola. Antibodies to T. gondii were found in 66.9, 51.7, and 18.6% of red foxes, arctic foxes and wolves, respectively. Significantly more adults than juveniles were antibody-positive for CDV in red foxes and arctic foxes, for CAV-1 in wolves, and for T. gondii in red foxes and wolves. There was a general tendency for adult female red foxes to have a higher prevalence of antibodies for CDV than adult males; this difference was statistically significant. The results indicate that CDV and CAV-1 are endemic in red foxes and wolves on the Scandinavian mainland and in arctic foxes on Svalbard. Although infection with L. interrogans serovar Icterohaemorrhagiae was relatively common in wild canids on mainland Norway, it was not found on Svalbard, where the maintenance host (Rattus norvegicus) is absent. All three species are commonly exposed to T. gondii through predation on infected intermediate hosts.

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.

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.