Nick G. H. Taylor

Aquatic systems: maintaining, mixing and mobilising antimicrobial resistance?

Bacteria showing antimicrobial resistance (AMR) pose a significant global healthcare problem. Although many mechanisms conferring AMR are understood, the ecological processes facilitating its persistence and spread are less well characterised. Aquatic systems represent an important milieu for the environmental release, mixing, persistence and spread of AMR bacteria and resistance genes associated with horizontally transferable genetic elements. Additionally, owing to the use and discharge of antimicrobials and biocides, and the accumulation and abundance of other pollutants, mechanisms that confer AMR might evolve in aquatic systems. In this review, we hypothesise that aquatic systems have an important ecological and evolutionary role in driving the persistence, emergence and spread of AMR, which could have consequences when attempting to reduce its occurrence in clinical settings.

The application of epidemiology in aquatic animal health -opportunities and challenges

Over recent years the growth in aquaculture, accompanied by the emergence of new and transboundary diseases, has stimulated epidemiological studies of aquatic animal diseases. Great potential exists for both observational and theoretical approaches to investigate the processes driving emergence but, to date, compared to terrestrial systems, relatively few studies exist in aquatic animals. Research using risk methods has assessed routes of introduction of aquatic animal pathogens to facilitate safe trade (e.g. import risk analyses) and support biosecurity. Epidemiological studies of risk factors for disease in aquaculture (most notably Atlantic salmon farming) have effectively supported control measures. Methods developed for terrestrial livestock diseases (e.g. risk-based surveillance) could improve the capacity of aquatic animal surveillance systems to detect disease incursions and emergence. The study of disease in wild populations presents many challenges and the judicious use of theoretical models offers some solutions. Models, parameterised from observational studies of host pathogen interactions, have been used to extrapolate estimates of impacts on the individual to the population level. These have proved effective in estimating the likely impact of parasite infections on wild salmonid populations in Switzerland and Canada (where the importance of farmed salmon as a reservoir of infection was investigated). A lack of data is often the key constraint in the application of new approaches to surveillance and modelling. The need for epidemiological approaches to protect aquatic animal health will inevitably increase in the face of the combined challenges of climate change, increasing anthropogenic pressures, limited water sources and the growth in aquaculture.

Salmonids Have an Extraordinary Complex Type I IFN System: Characterization of the IFN Locus in Rainbow Trout Oncorhynchus mykiss Reveals Two Novel IFN Subgroups

Fish type I IFNs are classified into two groups with two (group I) or four (group II) cysteines in the mature peptide and can be further divided into four subgroups, termed IFN-a, -b, -c, and -d. Salmonids possess all four subgroups, whereas other teleost species have one or more but not all groups. In this study, we have discovered two further subgroups (IFN-e and -f) in rainbow trout Oncorhynchus mykiss and analyzed the expression of all six subgroups in rainbow trout and brown trout Salmo trutta. In rainbow trout RTG-2 and RTS-11 cells, polyinosinic-polycytidylic acid stimulation resulted in early activation of IFN-d, whereas the IFN-e subgroup containing the highest number of members showed weak induction. In contrast with the cell lines, remarkable induction of IFN-a, -b, and -c was detected in primary head kidney leukocytes after polyinosinic-polycytidylic acid treatment, whereas a moderate increase of IFNs was observed after stimulation with resiquimod. Infection of brown trout with hemorrhagic septicemia virus resulted in early induction of IFN-d, -e, and -f and a marked increase of IFN-b and IFN-c expression in kidney and spleen. IFN transcripts were found to be strongly correlated with the viral burden and with marker genes of the IFN antiviral cascade. The results demonstrate that the IFN system of salmonids is far more complex than previously realized, and in-depth research is required to fully understand its regulation and function.

The anti-protozoal activity of bronopol on the key life-stages of Ichthyophthirius multifiliis Fouquet, 1876 (Ciliophora)

Pyceze™ (Novartis Animal Vaccines Ltd.) is licensed as a veterinary medicine to treat fungal infections in salmon, trout and their eggs. The active ingredient is bronopol, which due to its broad-spectrum activity has the potential to be an effective treatment against other important aquatic pathogens. In this study the efficacy of bronopol against Ichthyophthirius multifiliis was tested both in vitro and in vivo. In vitro trials demonstrated a 30 min exposure to 100 mg L(-1) bronopol killed 51.7% of the infective theronts. In vitro exposure of the protomonts to bronopol (0, 20, 50 and 100 mg L(-1)) for 30 min was observed to kill 0%, 76.2%, 97.2% and 100% respectively. Protomonts surviving treatment, demonstrated delayed development with the time taken from protomont until the release of theronts ranging from 28.3h for 0 mg L(-1) exposure, to 70 h for parasites in 20 and 50 mg L(-1) exposure groups. These concentrations also caused asymmetric cell division of the encysted tomonts. Exposure of encysted tomonts (min. 8 cell stage) to 100 mg L(-1) bronopol for 30 min, killed 50% within this period, with the remainder dying within the subsequent 42 h post exposure. Lower doses of bronopol were less effective in killing encysted tomonts than the higher doses (3.3% of parasites were killed in 20 mg L(-1); 10% in 50 mg L(-1)), but they still delayed theront release significantly (25.7 h for 0 mg L(-1) to 46.2h for parasites exposed to 20-50 mg L(-1)). Long, low dose (1 mg L(-1)) exposure to bronopol was also efficacious against theronts. Survival after 12h was 29% (c.f. 100% in control parasites), and <1% after 24 h exposure (c.f. 74% in control parasites). Theronts surviving these exposures demonstrated reduced infection success compared to control theronts. The findings of this study demonstrate that bronopol (Pyceze™) affects the survival of all free-living stages of I. multifiliis (protomonts, tomont and theronts), thus suggesting that bronopol may serve a useful role in the control of I. multifiliis infections.

Short-term exposure to a treated sewage effluent alters reproductive behaviour in the three-spined stickleback (Gasterosteus aculeatus)

Some UK sewage treatment work (STW) effluents have been found to contain high levels of anti-androgenic activity, but the biological significance of this activity to fish has not been determined. The aim of this study was to investigate the effects of exposure to a STW effluent with anti-androgenic activity on the reproductive physiology and behaviour of three-spined sticklebacks (Gasterosteus aculeatus). Fish were exposed to a STW effluent (50 and 100%, v/v) with a strong anti-androgenic activity (328.56±36.83 μgl(-1) flutamide equivalent, as quantified in a recombinant yeast assay containing the human androgen receptor) and a low level of oestrogenic activity (3.32±0.66 ngl(-1) oestradiol equivalent, quantified in a recombinant yeast assay containing the human oestrogen receptor) for a period of 21 days in a flow-through system in the laboratory. Levels of spiggin, an androgen-regulated protein, were not affected by the STW effluent exposure, nor were levels of vitellogenin (a biomarker of oestrogen exposure), but the reproductive behaviour of the males was impacted. Males exposed to full strength STW effluent built fewer nests and there was a significant reduction in male courtship behaviour for exposures to both the 50 and 100% STW effluent treatments compared with controls. The effect seen on the reproduction of male sticklebacks may not necessarily have been as a consequence of the endocrine active chemicals present in the STW effluent alone, but could relate to other features of the effluent, such as turbidity that can impair visual signalling important for courtship interactions. Regardless the specific causation, the data presented show that effluents from STW have an impact on reproductive behaviour in male sticklebacks which in turn affects reproductive performance/outcome. The study further highlights the use of fish behaviour as a sensitive endpoint for assessing potential effects of contaminated water bodies on fish reproduction.

Heat Wave–Associated Vibriosis, Sweden and Finland, 2014

During summer 2014, a total of 89 Vibrio infections were reported in Sweden and Finland, substantially more yearly infections than previously have been reported in northern Europe. Infections were spread across most coastal counties of Sweden and Finland, but unusually, numerous infections were reported in subarctic regions; cases were reported as far north as 65°N, ≈100 miles (160 km) from the Arctic Circle. Most infections were caused by non-O1/O139 V. cholerae (70 cases, corresponding to 77% of the total, all strains were negative for the cholera toxin gene). An extreme heat wave in northern Scandinavia during summer 2014 led to unprecedented high sea surface temperatures, which appear to have been responsible for the emergence of Vibrio bacteria at these latitudes. The emergence of vibriosis in high-latitude regions requires improved diagnostic detection and clinical awareness of these emerging pathogens.

The influence of risk factors on the abundance, egg laying habits and impact of Argulus foliaceus in stillwater trout fisheries.

Fishery managers perceive the ectoparasitic crustacean, Argulus foliaceus to be a cause of significant economic loss through reduced fish capture rates. This study investigates the influence of previously identified risk factors on the abundance, egg laying habits and impact of this parasite through a longitudinal study of five trout fisheries of varying management intensity. Low water clarity, slow stock turnover and high temperatures showed a significant association with a high abundance of A. foliaceus. High infection levels, low water clarity and low temperature were also associated with reduced rates of fish capture, suggesting abundance of A. foliaceus alone may not affect the catch rates. Depth of egg laying varied in each site throughout the study, increasing in depth as temperature and water clarity increased. Eggs were found to be most abundant in natural fish holding areas and it is hypothesized that the location of egg laying is determined by the habitat usage of host fish.

Effects of long duration, low dose bronopol exposure on the control of Ichthyophthirius multifiliis (Ciliophora), parasitising rainbow trout (Oncorhynchus mykiss Walbaum)

Ichthyophthirius multifiliis Fouquet, 1876 infections on intensively reared fish stocks can increase rapidly, which if left unmanaged, can result in the heavy loss of stock. The present study explores the efficacy of long duration, low dose (1, 2 and 5 mg L(-1)) treatments of bronopol (marketed as Pyceze™, Novartis Ltd.) in reducing the number of trophonts establishing on juvenile Oncorhynchus mykiss held under small scale culture conditions. The effect of bronopol on the colonisation success of infective theronts was also investigated by adding 2 mg L(-1) bronopol to the water prior and during the infection process. The number of parasites surviving on fish treated this way was compared to groups of fish that only received treatment after infection had occurred. The effect of bronopol on exiting trophonts throughout their external development to the point of theront release was also assessed through the delivery of 1 mg L(-1), 2 mg L(-1) and 5 mg L(-1) bronopol for up to 27 days consecutively (days 9-36 post-infection). The trial showed that a nominal dose of 2 mg L(-1) bronopol administered prior to infection significantly reduced the number of theronts surviving in the water column at the time of the initial challenge by 35-40% (P<0.05). Similarly, doses of 2 and 5 mg L(-1) bronopol administered as the first wave of mature I. multifiliis trophonts exited fish (i.e. day 11 onwards) to develop externally, reduced the number of trophonts establishing on fish as the second cycle of infection by 52-83%. Continuous application of 2 and 5 mg L(-1) bronopol throughout the second and third cycles of I. multifiliis infection gave further reductions of between 90 and 98%. The number of trophonts on the fish in the control tanks and those treated with 1 mg L(-1) and the 2 mg L(-1) dose at the time of initial infection, by comparison, were observed to increase with successive cycles of infection. From these small scale tank trials, this study demonstrates that the strategic, long duration, low dose delivery of drugs like bronopol can significantly reduce the number of trophonts establishing on fish suggesting the potential of this drug at managing I. multifiliis infections.

Using length-frequency data to elucidate the population dynamics of Argulus foliaceus (Crustacea: Branchiura)

This study uses a novel method for discriminating cohorts and investigating the population dynamics of the parasitic crustacean, Argulus foliaceus. Analysis of parasite length-frequency data was carried out in order to elucidate the timings and drivers behind the parasites life cycle. Up to 6 cohorts of the parasite emerge through the course of 1 year in still-water trout fisheries in England. Recruitment ceases over the winter months; however, 3 cohorts of the parasite over-winter, 2 as eggs and 1 as a hatched stage. The technique, when used in conjunction with temperature data, also allowed for the reliable prediction of growth rates and provided estimates of egg incubation times and the length of hatching periods. These data showed that growth rates increased exponentially between the observed temperatures of 4 to 22 degrees C. The method allowed for the time taken from hatching to egg laying under field conditions to be predicted and produced estimates that were validated against independent laboratory studies on the growth of the parasite.

Spring viraemia of carp (SVC) in the UK: the road to freedom.

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