Effects of regional coordination of salmon louse control in reducing negative impacts of salmonid aquaculture on wild salmonids

Parasitic salmon lice (Lepeophtheirus salmonis) are a constraint to the sustainable growth of salmonids in open net pens, and this issue has caused production to level off in recent years in the most aquaculture-intensive areas of Norway. The maximum allowed biomass at a regional level is regulated by using the so-called "traffic light" system, where salmon louse-induced mortality of migrating wild salmon post-smolts is evaluated against set targets. As a case study, we have investigated how a specific aquaculture-intensive area can reduce its louse levels sufficiently to achieve a low impact on wild salmon. Analyses of the output from a virtual post-smolt model that uses data on the reported number of salmon lice in fish farms as key input data and estimates the salmon louse-induced mortality of wild out-migrating Atlantic salmon post-smolts, suggested that female louse abundance on the local farms must be halved in spring to reach the goal implied by the traffic light system. The outcome of a modelling scenario simulating a proposed new plan for coordinated production and fallowing proved beneficial, with an overall reduction in louse infestations and treatment efforts. The interannual variability in louse abundance in spring, however, increased for this scenario, implying unacceptably high louse abundance when many farms were in their second production year. We then combined the scenario with coordinated production with other louse control measures. Only measures that reduced the density of farmed salmonids in open cages in the study area resulted in reductions in salmon louse infestations to acceptable levels. This could be achieved either by stocking with larger fish to reduce exposure time or by reducing fish numbers, e.g. by producing in closed units.

Simulated effects of increasing salmonid production on sea lice populations in Norway

Norway produces more than one million tonnes of salmonids every year, almost exclusively in open-water net pens. In 2014, the Norwegian government announced plans to increase salmonid production. However, increasing the number of farmed salmonids can have negative effects on the marine environment that threaten the industry's sustainability. In particular, production growth can lead to an increase in density-dependent diseases, including parasitic sea lice. The aim of this study was to simulate the effects of increased salmonid production on sea lice abundance using different scenarios for increasing the number of fish and for the management of sea lice. We used a previously developed, partly stage-structured model based on Norwegian production and environmental data to simulate the different scenarios. Our results show that increasing the marine farmed salmonid population at a national level by two or five times the current production leads to an increase in the sea lice abundance by 3.5% and 7.1%, respectively. We also found that by lowering the maximum allowable level of sea lice to an average of 0.049 adult females per fish, weekly treatments can be used to control sea lice population growth with a five times increase in production. However, this increases the number of farms treating per week by as much as 281.3%, which can lead to high costs and increased mortality among farmed salmonids. Overall, the results from our study shed light on the effects of increasing salmonid production in Norway with respect to the ongoing threat of sea lice infestations.

Surveillance of the Sensitivity towards Antiparasitic Bath-Treatments in the Salmon Louse (Lepeophtheirus salmonis)

The evolution of drug resistant parasitic sea lice is of major concern to the salmon farming industry worldwide and challenges sustainable growth of this enterprise. To assess current status and development of L. salmonis sensitivity towards different pesticides used for parasite control in Norwegian salmon farming, a national surveillance programme was implemented in 2013. The programme aims to summarize data on the use of different pesticides applied to control L. salmonis and to test L. salmonis sensitivity to different pesticides in farms along the Norwegian coast. Here we analyse two years of test-data from biological assays designed to detect sensitivity-levels towards the pesticides azamethiphos and deltamethrin, both among the most common pesticides used in bath-treatments of farmed salmon in Norway in later years. The focus of the analysis is on how different variables predict the binomial outcome of the bioassay tests, being whether L. salmonis are immobilized/die or survive pesticide exposure. We found that local kernel densities of bath treatments, along with a spatial geographic index of test-farm locations, were significant predictors of the binomial outcome of the tests. Furthermore, the probability of L. salmonis being immobilized/dead after test-exposure was reduced by odds-ratios of 0.60 (95% CI: 0.42–0.86) for 2014 compared to 2013 and 0.39 (95% CI: 0.36–0.42) for low concentration compared to high concentration exposure. There were also significant but more marginal effects of parasite gender and developmental stage, and a relatively large random effect of test-farm. We conclude that the present data support an association between local intensities of bath treatments along the coast and the outcome of bioassay tests where salmon lice are exposed to azamethiphos or deltamethrin. Furthermore, there is a predictable structure of L. salmonis phenotypes along the coast in the data, characterized by high susceptibility to pesticides in the far north and far south, but low susceptibility in mid Norway. The study emphasizes the need to address local susceptibility to pesticides and the need for restrictive use of pesticides to preserve treatment efficacy.

Sensitivity of Caligus rogercresseyi (Boxshall and Bravo 2000) to pyrethroids and azamethiphos measured using bioassay tests-A large scale spatial study

The variety of antiparasitics that can be used against caligid copepods is limited and efforts are needed to maintain their efficacies. The objective of this study was to monitor the sensitivity of Caligus rogercresseyi, populations towards antiparasitics based on deltamethrin, cypermethrin and azamethiphos within and across geographic regions. The bioassay design consisted of exposing parasites collected from 23 farms to the different chemotherapeutants at the concentration and exposure times recommended for field treatment, under laboratory conditions, and evaluating the number of dead and live parasites 48h after exposure. Parasites were collected from 23 farms distributed in four macrozones in the Los Lagos region and three macrozones in the Aysén region. Parasite sensitivity was evaluated using a Generalized Linear Mixed Model of the Binomial family (Logit) fit by the maximum likelihood, using the lme4 package in R. Parasite gender, macrozone, and antiparasitics were used as fixed factors and farm was the random factor. The model including all the factors proved to be a useful tool for predicting parasite sensitivity. This approach identified (i) those macrozones with a greater likelihood of finding parasite populations which are more or less sensitive to the three antiparasitics, (ii) cases in which parasite sensitivity to the different antiparasitics varied within a given macrozone, (iii) differences in sensitivity between females and males and (iv) an important random effect associated with farm. The results indicate a spatial variability of parasite sensitivity to antiparasitics which, added to the continuous treatments applied on farms, suggest it is necessary to regularly update the sensitivity status in the macrozones. This would allow managers to improve their decision making processes regarding the type of antiparasitic to be used in a given situation. The one-concentration type bioassay performed in this study allowed us to perform a large spatial study with replicated tests of the sensitivity of C. rogercresseyi to pyrethroids and azamethiphos. Further studies should focus on the farm effects, the relationship between the sensitivity of parasites and field efficacy, as well as parasite population structure and connectivity with regard to parasite transmission between farms.

Space-time modelling of the spread of pancreas disease (PD) within and between Norwegian marine salmonid farms

Infectious diseases are a constant threat to industrialised farming, which is characterised by high densities of farms and farm animals. Several mathematical and statistical models on spatio-temporal dynamics of infectious diseases in various farmed host populations have been developed during the last decades. Here we present a spatio-temporal stochastic model for the spread of a disease between and within aquaculture farms. The spread between farms is divided into several transmission pathways, including (i) distance related spread and (ii) other types of contagious contacts. The within-farm infection dynamics is modelled by a susceptible-infected-recovered (SIR) model. We apply this framework to model the spread of pancreas disease (PD) in salmon farming, using data covering all farms producing salmonids over 9 years in Norway. The motivation for the study was partly to unravel the spatio-temporal dynamics of PD in salmon farming and partly to use the model for scenario simulation of PD control strategies. We find, for example, that within-farm infection dynamics vary with season and we provide estimates of the timing from unobserved infection events to disease outbreaks on farms are detected. The simulations suggest that if a strategy involving culling of infectious cohorts is implemented, the number of detected disease outbreaks per year may be reduced by 57% after the full effect has been reached. We argue that the high detail and coverage of data on salmonid production and disease occurrence should encourage the use of simulation modelling as a means of testing effects of extensive control measures before they are implemented in the salmon farming industry.

Large scale modelling of salmon lice (Lepeophtheirus salmonis) infection pressure based on lice monitoring data from Norwegian salmonid farms

Infection by parasitic sea lice is a substantial problem in industrial scale salmon farming. To control the problem, Norwegian salmonid farms are not permitted to exceed a threshold level of infection on their fish, and farms are required to monitor and report lice levels on a weekly basis to ensure compliance with the regulation. In the present study, we combine the monitoring data with a deterministic model for salmon lice population dynamics to estimate farm production of infectious lice stages. Furthermore, we use an empirical estimate of the relative risk of salmon lice transmission between farms, that depend on inter-farm distances, to estimate the external infection pressure at a farm site, i.e. the infection pressure from infective salmon lice of neighbouring farm origin. Finally, we test whether our estimates of infection pressure from neighbouring farms as well as internal within farm infection pressure, predicts subsequent development of infection in cohorts of farmed salmonids in their initial phase of marine production. We find that estimated external infection pressure is a main predictor of salmon lice population dynamics in newly stocked cohorts of salmonids. Our results emphasize the importance of keeping the production of infectious lice stages at low levels within local networks of salmon farms. Our model can easily be implemented for real time estimation of infection pressure at the national scale, utilizing the masses of data generated through the compulsory lice monitoring in salmon farms. The implementation of such a system should give the salmon industry greater predictability with respect to salmon lice infection levels, and aid the decision making process when the development of new farm sites are planned.

Multivariate evaluation of the effectiveness of treatment efficacy of cypermethrin against sea lice (Lepeophtheirus salmonis) in Atlantic salmon (Salmo salar)

Background

The sea louse Lepeophtheirus salmonis is the most important ectoparasite of farmed Atlantic salmon (Salmo salar) in Norwegian aquaculture. Control of sea lice is primarily dependent on the use of delousing chemotherapeutants, which are both expensive and toxic to other wildlife. The method most commonly used for monitoring treatment effectiveness relies on measuring the percentage reduction in the mobile stages of Lepeophtheirus salmonis only. However, this does not account for changes in the other sea lice stages and may result in misleading or incomplete interpretation regarding the effectiveness of treatment. With the aim of improving the evaluation of delousing treatments, we explored multivariate analyses of bath treatments using the topical pyrethroid, cypermethrin, in salmon pens at five Norwegian production sites.

Results

Conventional univariate analysis indicated reductions of over 90% in mobile stages at all sites. In contrast, multivariate analyses indicated differing treatment effectiveness between sites (p-value < 0.01) based on changes in the proportion and abundance of the chalimus and PAAM (pre-adult and adult males) stages. Low water temperatures and shortened intervals between sampling after treatment may account for the differences in the composition of chalimus and PAAM stage groups following treatment. Using multivariate analysis, such factors could be separated from those which were attributable to inadequate treatment or chemotherapeutant failure.

Conclusions

Multivariate analyses for evaluation of treatment effectiveness against multiple life cycle stages of L. salmonis yield additional information beyond that derivable from univariate methods. This can aid in the identification of causes of apparent treatment failure in salmon aquaculture.

Within-farm spread of infectious salmon anemia virus (ISAV) in Atlantic salmon Salmo salar farms in Chile

Spread of infectious salmon anemia virus (ISAV) at the cage level was quantified using a subset of data from 23 Atlantic salmon Salmo salar farms located in southern Chile. Data collected from official surveillance activities were systematically organized to obtain detailed information on infectious salmon anemia (ISA) outbreaks. Descriptive statistics for outbreak duration, proportion of infected fish, and time to secondary infection were calculated to quantify the magnitude of ISAV incursions. Linear and multiple failure time (MFT) regression models were used to determine factors associated with the cage-level reproduction number (Rc) and hazard rate (HR) for recurrent events, respectively. In addition, the Knox test was used to assess if cage-to-cage transmissions were clustered in space and time. Findings suggest that within farms, ISA outbreaks, on average, lasted 30 wk (median = 26 wk, 95% CI = 24 to 37 wk) and affected 57.3% (95% CI = 47.7 to 67.0%) of susceptible cages. The median time to secondarily diagnosed cages was 23 d. Occurrence of clinical ISAV outbreaks was significantly associated with increased Rc, whereas increased HR was significantly associated with clinical outbreaks and with a large number of fish. Spatio-temporal analysis failed to identify clustering of cage cases, suggesting that within-farm ISAV spread is independent of the spatial location of the cages. Results presented here will help to better understand ISAV transmission, to improve the design of surveillance programs in Chile and other regions in which salmon are intensively farmed, and to examine the economic impact of ISAV and related management strategies on various cost and demand shifting factors.

Mortality related to pancreas disease in Norwegian farmed salmonid fish, Salmo salar L. and Oncorhynchus mykiss (Walbaum)

High mortality during the salmonid seawater phase is a continuous problem for the salmonid aquaculture industry, although the mortality levels show a large variation both in farms with a disease history and those without. We wanted to examine the mortality patterns in farms with pancreas disease (PD) and compare it to farms without this diagnosis. Further, we wished to investigate the factors influencing the maximum mortality in both groups. We examined data from all salmonid farms in Norway stocked after January 2003 and slaughtered before December 2007. In total, 1884 cohorts were included, and 150 of these were diagnosed with PD. We found that season accounted for more of the variation in mortality than water temperature in PD-positive cohorts and that infection pressure influenced the mortality in non-PD cohorts, suggesting outbreaks of disease that are not diagnosed. We also found that the mortality in PD cohorts decreased significantly from 2003 to 2007, suggesting that increased knowledge about PD and targeted actions have been effective. Our study further suggests that crude mortality figures may be of limited use when wanting to examine a particular disease and risk factors for increased mortality. We suggest farmers and legislation should turn to a more modern approach with cause-specific mortality records.

Low virulent infectious salmon anaemia virus (ISAV-HPR0) is prevalent and geographically structured in Norwegian salmon farming

Infectious salmon anaemia (ISA) is a severe disease in farmed Atlantic salmon Salmo salar that has caused epidemic outbreaks in most salmon-producing countries worldwide. The disease is caused by virulent ISA virus (ISAV). Low virulent variants of the virus, characterised by a full-length sequence in the highly polymorphic region of segment 6 in the virus genome, have been reported with increasing frequencies. These variants of the virus, termed HPR0, have been proposed to be ancestors of virulent ISAV. We examined this idea through studies of the phylogeographic and environmental distribution of ISAV-HPR0, as well as phylogeographic associations between virulent ISAV and ISAV-HPR0. Samples from 232 fish groups were screened for ISAV. Real-time RT-PCR was used for detection of ISAV, and the ISAV haemagglutinin esterase (HE) gene was characterised for positive samples. A Mantel test was used to test phylogeographic associations between pairs of ISAV-HPR0 HE gene sequences. A rank test was used to test associations between HE gene sequences from virulent ISAV and ISAV-HPR0. ISAV-HPR0 was detected in fish groups both in freshwater and marine environments, and in juveniles, on-grown marine salmon and broodstock salmon. Genetic and geographic distances between pairs of ISAV-HPR0 HE gene sequences were positively correlated, suggesting that the population of ISAV-HPR0 is geographically structured. Finally, we found a spatial association between fish groups with virulent ISAV (n = 21) and fish groups with ISAV-HPR0 (n = 27), supporting the hypothesis that ISAV-HPR0 may undergo a transition to virulent ISAV.

Development of a scalable image formation pipeline for multiscale gigapixel photography

We report on the image formation pipeline developed to efficiently form gigapixel-scale imagery generated by the AWARE-2 multiscale camera. The AWARE-2 camera consists of 98 "microcameras" imaging through a shared spherical objective, covering a 120° x 50° field of view with approximately 40 microradian instantaneous field of view (the angular extent of a pixel). The pipeline is scalable, capable of producing imagery ranging in scope from "live" one megapixel views to full resolution gigapixel images. Architectural choices that enable trivially parallelizable algorithms for rapid image formation and on-the-fly microcamera alignment compensation are discussed.

Sea lice as a density-dependent constraint to salmonid farming

Fisheries catches worldwide have shown no increase over the last two decades, while aquaculture has been booming. To cover the demand for fish in the growing human population, continued high growth rates in aquaculture are needed. A potential constraint to such growth is infectious diseases, as disease transmission rates are expected to increase with increasing densities of farmed fish. Using an extensive dataset from all farms growing salmonids along the Norwegian coast, we document that densities of farmed salmonids surrounding individual farms have a strong effect on farm levels of parasitic sea lice and efforts to control sea lice infections. Furthermore, increased intervention efforts have been unsuccessful in controlling elevated infection levels in high salmonid density areas in 2009-2010. Our results emphasize host density effects of farmed salmonids on the population dynamics of sea lice and suggest that parasitic sea lice represent a potent negative feedback mechanism that may limit sustainable spatial densities of farmed salmonids.

Modelling the spread of infectious salmon anaemia among salmon farms based on seaway distances between farms and genetic relationships between infectious salmon anaemia virus isolates

Infectious salmon anaemia (ISA) is an important infectious disease in Atlantic salmon farming causing recurrent epidemic outbreaks worldwide. The focus of this paper is on tracing the spread of ISA among Norwegian salmon farms. To trace transmission pathways for the ISA virus (ISAV), we use phylogenetic relationships between virus isolates in combination with space-time data on disease occurrences. The rate of ISA infection of salmon farms is modelled stochastically, where seaway distances between farms and genetic distances between ISAV isolates from infected farms play prominent roles. The model was fitted to data covering all cohorts of farmed salmon and the history of all farms with ISA between 2003 and summer 2009. Both seaway and genetic distances were significantly associated with the rate of ISA infection. The fitted model predicts that the risk of infection from a neighbourhood infectious farm decreases with increasing seaway distance between the two farms. Furthermore, for a given infected farm with a given ISAV genotype, the source of infection is significantly more likely to be ISAV of a small genetic distance than of moderate or large genetic distances. Nearly half of the farms with ISA in the investigated period are predicted to have been infected by an infectious farm in their neighbourhood, whereas the remaining half of the infected farms had unknown sources. For many of the neighbourhood infected farms, it was possible to point out one or a few infectious farms as the most probable sources of infection. This makes it possible to map probable infection pathways.

Use of molecular epidemiology to trace transmission pathways for infectious salmon anaemia virus (ISAV) in Norwegian salmon farming

BACKGROUND

Infectious Salmon Anaemia (ISA) is a disease affecting farmed Atlantic salmon, and most salmon producing countries have experienced ISA outbreaks. The aim of the present study was to use epidemiological and viral sequence information to trace transmission pathways for ISA virus (ISAV) in Norwegian salmon farming.

METHODS

The study covers a period from January 2007 to July 2009 with a relatively high rate of ISA outbreaks, including a large cluster of outbreaks that emerged in Northern Norway (the North-cluster). Farms with ISA outbreaks and neighbouring salmon farms (At-risk-sites) were tested for the presence of ISAV, and epidemiological information was collected. ISAV hemagglutinin-esterase (HE) and fusion (F) protein genes were sequenced and phylogenetic analyses were performed. Associations between sequence similarities and salmon population data were analysed to substantiate possible transmission pathways.

RESULTS

There was a high degree of genetic similarity between ISAV isolates within the North-cluster. ISAV was detected in 12 of 28 At-risk-sites, and a high proportion of the viruses were identified as putative low virulent genotypes harbouring the full length highly polymorphic region (HPR); HPR0 of the HE protein and the amino acid glutamine (Q) in the F protein at position 266. The sequences from HPR0/F (Q(266)) genotypes revealed larger genetic variation, lower viral loads and lower prevalence of infection than HPR-deleted genotypes. Seaway distance between salmon farms was the only robust explanatory variable to explain genetic similarity between ISAV isolates.

DISCUSSION

We suggest that a single HPR-deleted genotype of ISAV has spread between salmon farms in the North-cluster. Furthermore, we find that HPR0/F (Q(266)) genotypes are frequently present in farmed populations of Atlantic salmon. From this, we anticipate a population dynamics of ISAV portrayed by low virulent genotypes occasionally transitioning into virulent genotypes, causing solitary outbreaks or local epidemics through local transmission.

Integration of hydrodynamics into a statistical model on the spread of pancreas disease (PD) in salmon farming

Pancreas disease (PD) is an emerging disease in salmon farming caused by the salmonid alphavirus (SAV). SAV is evidently spread horizontally between neighbouring salmon farms, but whether such transmission occurs by passive drift in the water current or via fomites is not known. We tested whether hydrodynamic modelling contributes to explain the spread of PD, in which case SAV is likely to spread by passive drift. We present a simple logistic regression model that accounts for the effect of PD in the neighbourhood on the probability of acquiring PD in cohorts of farmed salmonids from an area on the west coast of Norway between 2005 and 2008. For a given cohort, we calculated infection pressure (IP) based on Euclidean distance, seaway distance or estimated water contact to sites with PD, and compared the amount of variance explained in the regression model by the different variants of IP. Water contact between a discharging farm site and a receiving site was calculated by simulating particle discharge using a hydrodynamic model. IP estimated by water contact was the best predictor of PD cases and controls in the model, which performed significantly better than IP estimated by seaway distance or Euclidean distance. Since the spread of PD in the study area was best explained by modelled water velocity, we conclude that PD is likely to be spread by passive drift of SAV in the water current.

Quantification of free-living Gyrodactylus salaris in an infested river and consequences for inter-river dispersal

Gyrodactylus salaris is a major threat to wild populations of Atlantic salmon Salmo salar in Norway. Inter-river dispersal of this parasite is considered to be mainly linked to infested fish. Dispersal through movement of contaminated water is considered possible but has not been quantitatively evaluated. To approach this problem, we built a simple model to estimate (1) the water concentration of free-living G. salaris and (2) the probability that given water volumes would contain free-living parasites. The concentration was back-estimated from reported experimental observations on the number of salmon juveniles found to be infected after being caged in a heavily infested river in Norway, protected from direct contact with the substrate or fish. Monte Carlo simulation was used to account for uncertainty and variability. The average concentration of G. salaris in the water column during the experiment was estimated to be 0.12 m(-3) (95% CI = 0.05 to 0.24). The probability that a given volume would contain at least 1 parasite was 1.2 x 10(-4) (95% CI = 5 x 10(-5) to 2.4 x 10(-4)) for 1 l, increasing to 0.67 (95% CI = 0.39 to 0.91) for 10,000 l. Thus, only high volumes were likely to represent a significant risk. Since we used data from a heavily infested spot, and despite the fact that time and space variations in water concentration of G. salaris may occur, we conclude that the risk of inter-river dispersal due to transfer of infested water through common river activities by humans is probably low.

A stochastic model for the assessment of the transmission pathways of heart and skeleton muscle inflammation, pancreas disease and infectious salmon anaemia in marine fish farms in Norway

Salmon farming is threatened, economically and ecologically, by infectious diseases. To reduce the risk of epidemics, authorities have developed regulations. These are based on quantitative understanding of pathways of infection, representing disease specific risks. A stochastic model was fitted to historical data, to estimate risk factors associated with competing spread mechanisms. Three infectious diseases were compared, heart and skeletal muscle inflammation (HSMI), pancreas disease (PD) and infectious salmon anaemia (ISA). This study was based on space-time data, from Norway from 2003 to 2007, describing the susceptible fish cohorts and the reported infections. Particular interest was given to seaway distances between farms and their local management organisation. The parameter measuring the effect of distance to an infectious fish farm was positive and significant for all diseases, implying that the risk involved with proximate infectious fish farms increased with decreasing distance. For HSMI and PD there was a significant effect of sharing a contact network with an infectious farm. For HSMI, but not for PD or ISA, there was a significant effect of previous infected cohorts on the same farm. The relative contribution of each transmission pathway was dominated by seaway distance for PD and HSMI, while other non-defined pathways dominated for ISA. This comparative study highlights that the three diseases have different patterns of spread, with important consequences for disease prevention and management.

Epidemiological investigation of infectious salmon anaemia (ISA) outbreaks in Norway 2003-2005

Epidemiological information was summarized from 32 outbreaks of infectious salmon anaemia (ISA) on salmon farming sites in Norway in 2003-2005. Virus isolates from the outbreak sites were genotyped, and the genotyping was used to assess possible associations between outbreak sites due to adjacent location, sharing fish farming authorisation, sharing smolt suppliers or sharing broodfish origin of the fish. The ISA outbreaks were distributed along most of the Norwegian coast and showed a variable clinical picture. The virus genotypes clustered into three genogroups. Pairs of outbreak sites matched for adjacent location or registered under the same authorisation, all shared genogroup, which was a significantly higher number of corresponding genogroups than expected by chance. For outbreak sites sharing smolt suppliers, corresponding genogroups appeared in 7 out of 12 matched pairs, which was not significant. An evaluation of broodfish origin associated with genogroups did not support transmission linked to broodfish origin. In conclusion, genotyping of virus isolates from ISA outbreaks supports associations between adjacent outbreaks. This is consistent with horizontal transmission. The present study failed to find evidence for vertical transmission (patterns of genogroups related to smolt suppliers or broodfish companies were not identified).

A stochastic model for infectious salmon anemia (ISA) in Atlantic salmon farming

Infectious salmon anemia (ISA) is one of the main infectious diseases in Atlantic salmon farming with major economical implications. Despite the strong regulatory interventions, the ISA epidemic is not under control, worldwide. We study the data covering salmon farming in Norway from 2002 to 2005 and propose a stochastic space-time model for the transmission of the virus. We model seaway transmission between farm sites, transmission through shared management and infrastructure, biomass effects and other potential pathways within the farming industry. We find that biomass has an effect on infectiousness, the local contact network and seaway distance of 5 km represent similar risks, but a large component of risk originates from other sources, among which are possibly infected salmon smolt and boat traffic.

Geographic risk factors for inter-river dispersal of Gyrodactylus salaris in fjord systems in Norway

Gyrodactylus salaris has been recorded in 46 Norwegian rivers since 1975 and is considered a threat to Atlantic salmon stocks. The primary introductions of G. salaris (primary infected rivers) have been accounted for by specific events, as reported in the literature. The parasite has subsequently dispersed to adjacent localities (secondary infected rivers). The objective of this paper is to address the occurrence of secondary infections by examining the hypothesis of inter-river dispersal of G. salaris. A dispersal model for the secondary river infections via migrating infected fish is proposed. Due to the limited tolerance of G. salaris to salinity, both freshwater inflow to dispersal pathways and dispersal distance were expected to influence the probability of inter-river dispersal. Eighteen rivers were categorised as primary infected rivers, 28 as secondary infected rivers, and 54 as rivers at risk. Four risk factors: the log10 freshwater inflow; the dispersal distance; the time at risk; and the salmon harvest were combined in a multi-variable logistic regression model of the probability of secondary infection. The final multi-variable model included log10 freshwater inflow (Wald chi-square = 9.93) and dispersal distance (Wald chi-square = 6.48). Receiver operating characteristic analyses of the final model supported freshwater inflow as a strong predictor of G. salaris infection status. The strong influence of the freshwater inflow on the probability of secondary infection adds further support to the hypothesis of inter-river dispersal of G. salaris through fjords.

Crabs, leeches and trypanosomes: an unholy trinity?

The red king crab Paralithodes camtschaticus was deliberately introduced to the Barents Sea in the 1960s and 1970s from its native area in the North Pacific. The carapace of these crabs is a favoured substrate for the leech Johanssonia arctica to deposit its eggs, and the leech is a vector for a trypanosome blood parasite of marine fish, including cod. We examined cod for trypanosome infections during annual cruises along the coast of Finnmark in North Norway over three successive years from stations along a gradient of over 1000 km. In every year the level of trypanosome infection in cod was significantly highest in the area with the greatest density of king crabs. We propose the hypothesis that the burgeoning population of red king crabs in this area is indirectly responsible for increased transmission of trypanosomes to cod by promoting an increase in the population of the leech vector.

Risk of extrapyramidal syndromes with haloperidol, risperidone, or olanzapine

OBJECTIVE

To compare the risk of extrapyramidal syndrome (EPS) between risperidone, olanzapine, and haloperidol, taking into account patients' past antipsychotic drug use and past EPS.

METHODS

Data were obtained from the PHARMO-database, containing filled prescriptions of 450,000 community-dwelling people in the Netherlands from 1986 through 1999. We defined cohorts of first-time users of haloperidol, risperidone, or olanzapine aged 15 to 54 years. In the first 90 days of treatment, we assessed the occurrence of EPS, defined as first use of any antiparkinsonian agent. We estimated relative risks of EPS for risperidone and olanzapine versus haloperidol using a Cox proportional hazards model. Patients were subdivided according to prior use of antipsychotic and antiparkinsonian drugs.

RESULTS

We identified 424 patients starting treatment with haloperidol, 243 with risperidone, and 181 with olanzapine. Prior use of antipsychotic plus antiparkinsonian medication was significantly more frequent among users of risperidone and olanzapine than in those using haloperidol (36.2%, 40.3%, and 4.5%, respectively; p < 0.001). Within most subgroups of comparable treatment history, patients using risperidone and olanzapine showed reduced risks of EPS compared with haloperidol, although some of these findings did not reach statistical significance (RR 0.03-0.22). However, this was not observed for patients using risperidone who had experienced EPS in the past (RR 1.30; 95% CI 0.24 to 7.18).

CONCLUSIONS

In general, we observed reduced risks of EPS for risperidone and olanzapine compared with haloperidol within subgroups of patients with a similar treatment history. However, the added value of risperidone in patients who have experienced EPS in the past needs further study.

Estimation of incidence and prevalence of Parkinson's disease in the elderly using pharmacy records

PURPOSE

We determined the prevalence and incidence of Parkinson's disease among persons aged 55 years and older in pharmacy records.

METHODS

Data came from the PHARMO database which includes information on drug dispensing for all residents of six Dutch cities. We selected all persons aged 55 years and older who had used antiparkinsonian drugs, and calculated a chance for having Parkinson's disease with use of a previously validated logistic regression model. We used a cut-off of 0.5 (sensitivity 62%, positive predictive value 92%). Prevalence was estimated on the first Wednesday of October 1997, incidence on the first Wednesday of October 1993 until 1997. A patient was incident, if the first prescription for an anti-parkinsonian drug was dispensed at least 180 days after entry into PHARMO. Prevalence and incidence were standardized to the Netherlands population of 1 January 1998. The prevalence was adjusted for the sensitivity and positive predictive value of the model.

RESULTS

The unadjusted prevalence (per 100,000) for those aged 55-64 years was 111, 65-74 years 598, 75-84 years 1551 and for persons aged 85 years and older 1847. The adjusted and standardized prevalence was 970 per 100,000 (95% confidence interval 869 to 1071). The incidence (per 100,000 person years) for persons aged 55-64 years was 12, 65-74 years 108, 75-84 years 257 and for persons aged 85 years and older 247. The standardized incidence was 109 per 100,000 person years (96 to 121).

CONCLUSIONS

Prevalence and incidence were in range with the literature. Pharmacy records therefore seem to be a useful tool for continuous monitoring of incidence and prevalence of Parkinson's disease.

Antipsychotic-induced extrapyramidal syndromes. Risperidone compared with low- and high-potency conventional antipsychotic drugs

AIM

To compare the risk of extrapyramidal syndromes (EPS) between patients using risperidone and those using low-potency conventional antipsychotic drugs (APDs) in outpatient clinical practice, as measured by the use of anticholinergic medication. We tried to replicate results from previous clinical trials that compared risperidone with high-potency APDs.

METHOD

Data was obtained from the PHARMO database containing filled prescriptions of 450,000 community-dwelling people in The Netherlands from 1986 to 1998. From the patients aged 15-54 years who had been newly treated with APDs, we defined mutually exclusive cohorts according to the APD first prescribed to a patient. APD exposure was followed until the first prescription of anticholinergic medication and was censored when APD prescribing was interrupted or switched. We estimated relative risks between risperidone and commonly used low-potency and high-potency APDs using Cox proportional hazards models, adjusting for age, gender, dose and other potential confounders.

RESULTS

In 4094 patients who had been newly prescribed antipsychotic drugs, the overall incidence rate of anticholinergic drug therapy was 556 per 1000 person-years, which was dose dependent. Prescribed doses of all antipsychotics were low. While, in accordance with previous trials, risperidone showed a lower risk of EPS than the high potency APDs such as haloperidol (RR 0.26; 95% CI 0.10-0.64), we did not observe a lower EPS rate than low-potency APDs (risperidone vs thioridazine RR 1.73, 95% CI 0.49-6.13; risperidone vs pipamperone RR 2.50, 95% CI 0.78-8.04).

CONCLUSION

The reduced EPS rates observed when comparing risperidone with high-potency antipsychotics such as haloperidol may not apply to comparisons with low-potency drugs.

Quick titration of pergolide in cotreatment with domperidone is safe and effective

The purpose of the study was to analyze efficacy and safety of quick pergolide titration combined with domperidone. In an open-label prospective study, pergolide was titrated in 16 days to a maximum of 3 mg/d doses as adjunctive treatment to L-Dopa in 10 elderly patients with Parkinson's disease. Sixty milligrams domperidone was started 2 days before and and continued during the pergolide titration period to prevent side effects. Adverse events were studied for 6 weeks. Efficacy was measured with the motor part ("on" condition) of the Unified Parkinson's Disease Rating Scale (UPDRS), the 2-minute walking test, the Timed Up and Go test, and the Postural-Locomotor-Manual test. After quick titration of pergolide with domperidone cotreatment, no symptomatic side effects were seen except for lightheadedness in one patient, which disappeared after dose reduction. The UPDRS motor score improved significantly from 21 +/- 8 at baseline to 16 +/- 7 and 12 +/- 7 after 1 and 2 weeks, respectively. The 2-minute walking distance improved significantly from 123 +/- 36 m at baseline to 136 +/- 41 m after 6 weeks. The Timed Up and Go and Postural-Locomotor-Manual test results, overall, did not show significant changes. Quick titration of pergolide to a maximum of 3 mg/d with domperidone cotreatment is safe and effective. Therefore, we recommend domperidone cotreatment in the titration period to prevent unnecessary failure of dopamine agonist treatment because of adverse effects.

Muscle strength, functional mobility and vitamin D in older women

Vitamin D deficiency may lead to loss of type II muscle fibres, and thereby to atrophy of proximal muscles with an increased risk of falling and bone fractures. The aim of the study was to determine if six months of vitamin D treatment (0.5 microg alphacalcidol) could positively influence values for muscle strength and functional mobility in vitamin D-deficient older women. Twenty-seven women entered the study which took place at a teaching hospital outpatient department. Ten vitamin D-deficient (serum 25(OH)D3 <20 nmol/L) older (>70 years) women and 13 age-matched female subjects with normal vitamin D levels (serum 25(OH)D3 >30 nmol/L) completed the study. Preand post-treatment data were obtained for isometric knee extensor strength, handgrip strength and functional mobility (walking distance over 2 minutes and the timed i'Up & Go" test). Six months of treatment with alphacalcidol led to significant improvements (compared to the controls) in values of isometric knee extensor strength (left leg: 14.6% +/- 5.7%. p=0.03; right leg: 11.5% +/- 5.0%, p=0.02) (mean +/- SEM). The achievements in the timed "Up & Go" test and 2-minute walking test did not improve in the alphacalcidol group compared to the controls after 6 months. However, within the vitamin D-deficient group, 6 months of alphacalcidol treatment led to a significant increase in the walking distance over 2 minutes (increase from 137.6 +/- 12.6 to 151.3 +/- 11.2 meters, p=0.03). The controls, with normal vitamin D levels, did not exhibit improvements in performance of any of the tests over a period of 6 months. Summarized, alphacalcidol seems to improve muscle strength and walking distance over 2 minutes in vitamin D-deficient older women.

Lactic acid bacteria associated with the digestive tract of Atlantic salmon (Salmo salar L.)

The present study reports the effect of excessive handling stress and starvation on the lactic acid bacteria associated with the digestive tract of Atlantic salmon (Salmo salar L.). A relatively low population level (approximately 2 x 103 bacteria per gram wet tissue) of viable adherent heterotrophic bacteria was associated with the digestive tract (foregut, midgut and hindgut). Of the 752 bacterial isolates isolated from diet, water and the digestive tract, 201 isolates belonged to the carnobacteria. Of these isolates, one from the diet, one from the rearing water and 80 from the gastrointestinal tract, were further identified on the basis of 16S rDNA sequence analysis. All these isolates were identified as being Carnobacterium piscicola-like. Daily repeated stress and starvation of the fish over 11 d had no influence on the total culturable bacterial numbers or population level of C. piscicola associated with the digestive tract. C. piscicola-like isolates colonizing the various intestinal regions (foregut, midgut and hindgut) were also screened for their ability to produce growth inhibitory compounds active against the fish pathogen Aeromonas salmonicida. Of the 199 C. piscicola isolates tested, 139 inhibited growth of the pathogen.

Effect of a program of diverse activities on disturbed behavior in three severely demented patients

The effects of a daily program of various activities on disturbed behavior were studied prospectively in three patients with severe dementia. Prior to the study, patients had not responded to treatment with benzodiazepines and/or neuroleptics. The study consisted of three periods, each lasting for 4 weeks: i.e., baseline, intervention, and follow-up. During each period, behavior was assessed by means of observation scales: GIP, SDAS, and CGI. Psychotropic medication was held as constant as possible. During intervention, the patients took part in a program of activities, including group, musical, physical, and social activities. During baseline and follow-up, patients followed the regular ward activities. The patients showed different responses, probably related to personal interests. Possible implications for the treatment of patients with dementia, complicated by disturbed behavior, and suggestions for future research are discussed. The enthusiasm of the nursing staff dealing with these patients was a promising result.

[Drug use on admission and discharge in a geriatric department of a psychiatric hospital]

Change in medication use was studied in patients admitted to a short-stay geriatric ward of a psychiatric hospital. One hundred ten patients were followed up until discharge from the short-stay ward, or, after transfer, until discharge from the medium-stay ward to home or to a nursing-home. Mean drug use on admission was 2.6 drugs; at discharge mean use was 2.1 drugs. Drugs most prescribed at admission were neuroleptics (41%) and benzodiazepines (39%). At discharge 15% used neuroleptics and 22% benzodiazepines. A reduction in use of cardiovascular drugs, and especially of digoxin, was found. Prescription of laxatives and vitamins, especially folic acid and vitamin B12, increased. In comparison with studies on two other geriatric wards in general hospitals in The Netherlands the most marked difference was a reduction of 17% in this study of the number of patients using benzodiazepines on discharge in contrast to an increase of 18 and 3% in the two other studies. The number of patients using neuroleptics on discharge decreased in the present study with 26%; in the two other studies respectively a decrease of 7% and a constant prescription level was found.

The population age structure and reproductive biology of Gyrodactylus salaris Malmberg (Monogenea)

Gyrodactylus salaris has recently become a major pathogen of Atlantic Salmon (Salmo salar) in Norway. The survivorship, population age structure and pattern of insemination of G. salaris were studied to determine the extent to which this species reproduces sexually. The age-specific mortality schedule of G. salaris could be described by an exponential model but day to day variations were large, with an increase in mortality after each birth. Modelling population growth using the best fit mortality schedule indicated that, at stable age structure, 35% of the population would consist of newborn and pre-1st birth flukes. Using testis, penis and embryo development, pre-1st birth and immediately post-1st birth flukes could be unambiguously identified, and established infections were found to contain 35% pre-1st birth flukes, as predicted. The proportion of pre-1st birth flukes in newly established infections was significantly smaller, probably because of differences in the rate of transmission between newborn and older flukes. Gyrodactylus salaris is relatively long-lived, and more than 40% of the population may survive to give birth for the third time. As gyrodactylids are protogynous, and the first daughter is probably produced asexually, this long-lived strategy ensures that a large part of the G. salaris population possesses a functional male system, and that the asexually derived flukes are a smaller component of the total population in this species. Flukes with whorls of inseminated spermatozoa within the seminal receptacle were found in all age groups possessing a functional male system, and were interpreted as having been cross-inseminated.(ABSTRACT TRUNCATED AT 250 WORDS)

Temperature-dependent reproduction and survival of Gyrodactylus salaris Malmberg, 1957 (Platyhelminthes: Monogenea) on Atlantic salmon (Salmo salar L.)

The relationship of survival and reproduction of Gyrodactylus salaris Malmberg on the Atlantic salmon (Salmo salar) to water temperature (2.5-19.0 degrees C), was studied on the basis of temporal sequence of births and age at death of individual parasites on isolated salmon, and of infrapopulation growth on isolated and grouped salmon. Mean life-span of the parasite was negatively correlated with water temperature: 33.7 days at 2.5 degrees C and 4.5 days at 19.0 degrees C. The average number of offspring per parasite peaked between 6.5 and 13.0 degrees C, and was approximately 2.4 at these two temperatures. Both the period between the successive births of the offspring (max 4) and the estimated generation time were negatively correlated with temperature. The innate capacity for increase (rm) was positively correlated with temperature: from 0.02 (/parasite/day) at 2.5 degrees C to 0.22 (/parasite/day) at 19.0 degrees C. Growth of the infrapopulations was positively correlated with water temperature and was higher on isolated fish than on grouped fish, though less than the potential parasite population growth estimated from rm. In the infrapopulations the mean intensity of parasites continued to increase throughout all the experiments on both isolated fish and on grouped fish.

Lithium augmentation in geriatric depression

In the geriatric department of a Dutch psychiatric hospital the charts of 51 patients treated with lithium in addition to cyclic antidepressants were reviewed. A response was seen in 33 patients (65%). For patients with recurrent depressive episodes, a statistical trend was found towards more responders with more complete responses, compared to patients with first depressive episodes. During lithium augmentation, 10 patients suffered from severe adverse effects 12 times. In spite of adverse effects, with expert monitoring lithium augmentation can, in our opinion, be of value in the treatment of older depressed patients.

[Lithium in the treatment of depressed elderly patients]

In the geriatric department of a Dutch psychiatric hospital the charts of 65 patients treated with lithium for depression were reviewed. We assessed efficacy and adverse effects. The sample included 65 patients, 12 men and 53 women, mean age 77 (64-91) years. A complete or partial response was seen in 30 out of 43 patients (70%) treated with lithium in addition to a cyclic antidepressant. Six out of 22 patients treated with lithium as a sole antidepressant responded completely or partially. During lithium therapy 16 patients suffered from severe adverse effects. In our view and in spite of severe adverse effects, with expert monitoring lithium can be of value in the treatment of (very) old and depressed patients.

Pharmacokinetics of high-dosage naproxen in elderly patients

After multiple oral doses of 500 mg naproxen twice daily, eight young healthy male volunteers and six male and female elderly patients participated in a pharmacokinetic study. Serum naproxen levels were measured by high-pressure liquid chromatography; protein-unbound drug was determined after equilibrium dialysis. A significantly lower maximal serum concentration (Cpeak), smaller area under the curve during one dose interval [AUC(0-12)], larger total body clearance (CL/F) and apparent volume of distribution (V/F body wt-1) were found for the total drug in elderly patients. The pharmacokinetics of the protein-unbound drug showed higher trough and peak concentrations, larger AUC(0-12)u, and smaller (CL/F)u and (V/F)u in the elderly patients. The unbound fraction (less than 1% of total naproxen) showed concentration dependency; in the elderly, a larger unbound fraction was found. Pharmacokinetic differences between the elderly and the young may be explained by a lower serum albumin concentration in the aged, together with a decrement in binding affinity of naproxen to albumin; moreover, the clearance of unbound drug was significantly reduced in the elderly (281 +/- 96 l/h) as compared with the young (713 +/- 164 l/h). We conclude that age-related factors increase serum unbound naproxen concentrations. It is, therefore, advisable to start treatment with naproxen in the elderly at a low dosage.

Blood pressure and both venous and urinary catecholamines after cerebral infarction

Blood pressure, both venous and urinary catecholamines and plasma renin activity (PRA) were studied in 10 patients (6 men and 4 women, mean age 70 +/- 10 years) on the first three days after cerebral infarction. Blood pressure fell significantly (p less than 0.02) on the second and third day after stroke. There was a small but significant (p less than 0.01) decrease in plasma epinephrine concentration on the third day. The norepinephrine values remained constant on the three days. The PRA showed a significant (p less than 0.01) rise on the third day. No significant correlation was detected between the course of the blood pressure and the plasma catecholamines or PRA. When blood pressure was correlated with the urinary catecholamines, however, a significant correlation with epinephrine (r = 0.45; p less than 0.05) and with norepinephrine (r = 0.44; p less than 0.05) was found. We conclude that the changes in blood pressure after stroke are at least partly mediated by the changes in catecholamine production.

Course of blood pressure after cerebral infarction and transient ischemic attack

In 63 patients, admitted for cerebral infarction or transient ischemic attack (TIA), the blood pressure course was studied. The blood pressure before the event was studied retrospectively; 32 patients were normotensive, in 31 patients existed hypertension, with antihypertensive treatment in 15 of these cases. The blood pressure after the event was studied prospectively, and turned out to be risen in 67% of the patients on the day of admission. It fell in the first day after infarction or TIA, mainly on the second day, to a plateau level reached on the fifth day. Only 3 patients (5%) remained hypertensive until discharge from the hospital. In 48 patients blood pressure values were available as measured two to six months after discharge, without a change in antihypertensive medication. Blood pressure was increased compared to the value measured before discharge. In 14 patients (29%) hypertensive blood pressure figures were measured at that time. It is concluded that blood pressure is elevated in the acute phase of cerebral infarction and TIA, but falls spontaneously in the first days to normotensive levels in most patients; because blood pressure may increase again, measurements of blood pressure within the first months after discharge are needed.

Contribution of inappropriate treatment for hypertension to pathogenesis of stroke in the elderly

One hundred and seventy eight patients admitted to hospital with acute cerebral infarction or transient ischaemic attack were studied to determine if their treatment had been changed during the previous three weeks and to compare their blood pressure after the stroke with premorbid values. Blood pressure measurements taken within one year before the stroke were available for 100 patients; seven of these had had a recent change in antihypertensive or diuretic treatment. Of these, three patients who had started taking frusemide because of hypertension and one whose dosage of a reserpine combination drug had been increased experienced an appreciable decrease in blood pressure immediately after the stroke; they also showed signs of haemoconcentration. The change in treatment probably contributed to the stroke in these four patients. The other three showed a smaller decrease or even an increase in blood pressure and no signs of haemoconcentration; the relation between the change in treatment and stroke is less likely in these patients. The use of high ceiling diuretics such as frusemide in the treatment of hypertension may induce hypovolaemia and hypotension, resulting in cerebral ischaemia, and are therefore best avoided in such treatment.

Antihypertensive treatment as a possible cause of stroke in the elderly

There have been a few reports on stroke as a side-effect of antihypertensive treatment. To study the occurrence of this side-effect, a questionnaire was sent to all Dutch nursing homes (n = 322). Thirty patients were reported with signs of cerebral ischaemia shortly after starting antihypertensive and diuretic drugs. Nine of these cases were well documented with full data on blood pressure, measured immediately after the event and compared with pretreatment levels. A review of cases reported in the literature is presented. It is concluded that, especially in elderly patients, an abrupt fall in blood pressure may induce cerebral ischaemia, sometimes resulting in stroke. Antihypertensive treatment in the elderly should therefore start with a small dose, the aim being to reduce blood pressure gradually.

Nucleotide content of isolated bovine rod outer segments

Endogenous nucleotide levels of isolated intact ROS were analyzed by high pressure liquid chromatography. Intact bovine ROS showed a total nucleotide concentration of 1.0 mM, ATP and GTP being the major components (0.1-0.2 mol per mol of rhodopsin). When intact ROS resuspended in sucrose-ficoll medium were diluted in a Ringer-Krebs bicarbonate, the nucleotide ratios were markedly changed, but the total concentration remained unchanged. The concentration of cyclic nucleotides (cAMP and cGMP) was markedly enhanced when ROS were placed in Ringer buffer, whereas ATP and GTP concentration was reduced. Total nucleotide concentration is 100% higher in intact than in leaky plasma membrane ROS. Upon illumination, no change was observed in the nucleotide levels of ROS in sucrose-ficoll medium. However ATP, GTP and cAMP levels were reduced when ROS in Ringer medium were exposed to light while cGMP concentration showed no change. Relevance of relative nucleotide content and ionic concentration to the transduction phenomenon in photoreceptor is discussed.