• The advantages of the use of discs containing single agents in disc diffusion testing of the susceptibility of Aeromonas salmonicida to potentiated sulphonamides

      Douglas, I.; Ruane, N.M.; Geary, M.; Carroll, C.; Fleming, G.T.A.; McMurray, J.; Smith, P. (Elsevier, 2007)
      The susceptibilities of 106 strains of Aeromonas salmonicida to trimethoprim/sulfamethoxazole (SFT) were determined in two laboratories using the Clinical and Laboratory Standards Institute's M42-A disc diffusion protocols. The data generated by the use of discs containing 25 μg SFT (SFT25) allowed the strains to be placed into two groups. Strains in one group (17 strains) generated no inhibition zones and the zones obtained from the other 89 strains were distributed over a wide range but showed no natural division into separate sub-classes. A further investigation performed by one of the participating laboratories, of the susceptibility of 91 of these 106 strains used discs containing 100 μg sulfmethoxazole (SFM100) and 5 μg trimethoprim (TMP5). Application of normalised resistance interpretation to these data allowed the estimation of epidemiological cut-off values for WT strains of ≥ 9 mm for SFM100 and ≥ 21 mm for TMP5. This investigation demonstrated the presence of three distinct phenotypic classes, one containing strains manifesting wild type susceptibility to both agents, another containing strains manifesting non-wild type susceptibility to both and a third containing strains manifesting wild type susceptibility with respect to TMP but non-wild type with respect to SFM. Analysis demonstrated the inability of SFT25 discs to generate data that allowed the separate identification of strains that were fully susceptible to both TMP and SFM from those that were fully susceptible to TMP but were not fully susceptible to SFM. It is recommended that, in investigation of the susceptibility to potentiated sulphonamides of isolates from diseased fish, separate discs, containing the individual components of the mixture, should be employed.
    • Biofouling of the hydroid Ectopleura larynx on aquaculture nets in Ireland: implications for finfish health

      Baxter, E.J.; Sturt, M.M.; Ruane, N.M.; Doyle, T.K.; McAllen, R.; Rodger, H.D. (Fish Veterinary Society, 2012)
      The potential direct health problems posed to marine-farmed salmonids by the biofouling hydroid Ectopleura larynx (Phylum Cnidaria, Class Hydrozoa) and in situ net washing processes to remove the fouling organisms have not yet been addressed. In an attempt to address the possible impacts, the rate of E. larynx growth on aquaculture nets over a net-cleaning cycle was assessed and Atlantic salmon (Salmo salar) smolts were exposed to hydroid-biofouled nets under experimental challenge. After only 1 week of immersion, there was a high settlement of E. larynx on net panels, with the maximum growth observed after 3 week of immersion. For the challenges trials, experimental treatment groups of S. salar were exposed to hydroid net panels or loose hydroid material for 11 hours under controlled conditions. Gills were examined for signs of gross damage and assigned a histopathological gill score. Prior to the experiment, the gills were healthy and did not show signs of damage from any insult. After exposure to E. larynx, focal areas of epithelial sloughing, necrosis and haemorrhage were visible on the gills under histopathology and a maximum gill score of 4 was observed. These results are the first in an investigation of this kind and suggest that E. larynx can damage the gills of S. salar. Further work on this area is vital to develop a better understanding of the pathogenesis of the damage caused by hydroids and their long-term effects on fish health, growth and survival.
    • Gill damage to Atlantic salmon (Salmo salar) caused by the common jellyfish (Aurelia aurita) under experimental challenge

      Baxter, E.J.; Sturt, M.M.; Ruane, N.M.; Doyle, T.K.; McAllen, R.; Harman, L.; Rodger, H.D. (PLoS ONE, 2011)
      Background: Over recent decades jellyfish have caused fish kill events and recurrent gill problems in marine-farmed salmonids. Common jellyfish (Aurelia spp.) are among the most cosmopolitan jellyfish species in the oceans, with populations increasing in many coastal areas. The negative interaction between jellyfish and fish in aquaculture remains a poorly studied area of science. Thus, a recent fish mortality event in Ireland, involving Aurelia aurita, spurred an investigation into the effects of this jellyfish on marine-farmed salmon. Methodology/Principal Findings: To address the in vivo impact of the common jellyfish (A. aurita) on salmonids, we exposed Atlantic salmon (Salmo salar) smolts to macerated A. aurita for 10 hrs under experimental challenge. Gill tissues of control and experimental treatment groups were scored with a system that rated the damage between 0 and 21 using a range of primary and secondary parameters. Our results revealed that A. aurita rapidly and extensively damaged the gills of S. salar, with the pathogenesis of the disorder progressing even after the jellyfish were removed. After only 2 hrs of exposure, significant multi-focal damage to gill tissues was apparent. The nature and extent of the damage increased up to 48 hrs from the start of the challenge. Although the gills remained extensively damaged at 3 wks from the start of the challenge trial, shortening of the gill lamellae and organisation of the cells indicated an attempt to repair the damage suffered. Conclusions: Our findings clearly demonstrate that A. aurita can cause severe gill problems in marine-farmed fish. With aquaculture predicted to expand worldwide and evidence suggesting that jellyfish populations are increasing in some areas, this threat to aquaculture is of rising concern as significant losses due to jellyfish could be expected to increase in the future.
    • Impact of inter-lab variation on the estimation of epidemiological cut-off values for disc diffusion susceptibility test data for Aeromonas salmonicida

      Smith, P.; Ruane, N.M.; Douglas, I.; Carroll, C.; Kronvall, G.; Fleming, G.T.A. (Elsevier, 2007)
      Two laboratories investigated the susceptibility of 106 Aeromonas salmonicida strains (from Denmark, France, Ireland, Norway and Scotland) to erythromycin, gentamicin, oxytetracycline and oxolinic acid using the disc diffusion protocols (M42-A) published by the Clinical and Laboratory Standards Institute. In studies of susceptibility to florfenicol an additional 15 Canadian strains were included. Comparison of the data generated by the two laboratories demonstrated that for each disc both detected a similar pattern of distribution but that there was a significant numerical difference in the zone sizes they recorded. Analysis of the extent of this lateral shift between the data generated in two laboratories indicated that the application of a single laboratory-independent epidemiological cut-off value for each disc could result in disagreement between the laboratories as to whether a strain should be classified as wild-type or non wild-type. Normalised resistance interpretation was employed to generate epidemiological cut-off values from the data obtained by each laboratory. The use of these laboratory-specific cut-off values resulted in both laboratories achieving complete agreement as to the classification of all strains to all agents.
    • Isolation of Streptococcus agalactiae and an aquatic birnavirus from doctor fish Garra rufa L.

      Ruane, N.M.; Collins, E.M.; Geary, M.; Swords, D.; Hickey, C.; Geoghegan, F. (BioMed Central, 2013)
      Background The doctor fish, Garra rufa, has become increasingly popular as a treatment for skin disorders and for pedicures in recent years. Despite this there is very little information available regarding the welfare of these fish and the range of potential pathogens they may carry. In this study, a group of fish suffering from post-transport mortalities were examined and the isolated pathogens identified. Findings Group B Streptococcus agalactiae was isolated from kidney swabs of the fish and found to be resistant to a number of antibiotics. In addition to this, a fish virus belonging to the aquabirnavirus group, serogroup C was isolated for the first time in Ireland. However, no clinical signs of disease typical of bacterial or viral infections were observed in any fish examined. Conclusions As no clinical signs of disease attributable to either of the pathogens identified were found it was concluded that the mortalities were most likely due to transport related stress exacerbated by the presence of the pathogens. Further work is required to assess the suitability of current transport strategies and to examine the potential risk associated with the transport of live ornamental fish.
    • A longitudinal study of amoebic gill disease on a marine Atlantic salmon farm utilising a real-time PCR assay for the detection of Neoparamoeba perurans

      Downes, J.K.; Henshilwood, K.; Collins, E.M.; Ryan, A.; O'Connor, I.; Rodger, H.D.; MacCarthy, E.; Ruane, N.M. (Inter Research, 2015)
      Amoebic gill disease (AGD) is a proliferative gill disease of marine cultured Atlantic salmon Salmo salar, with the free-living protozoan Neoparamoeba perurans being the primary aetiological agent. The increased incidence of AGD in recent years presents a significant challenge to the Atlantic salmon farming industry in Europe. In this study, a real-time TaqMan® PCR assay was developed and validated to detect Neoparamoeba perurans on Atlantic salmon gills and further used to monitor disease progression on a marine Atlantic salmon farm in Ireland in conjunction with gross gill pathology and histopathology. The assay proved specific for N. perurans, with no cross-reactivity with the related species N. pemaquidensis, N. branchiphila or N. aestuarina, and was capable of detecting 2.68 copies of N. perurans DNA μl−1. Although the parasite was detected throughout the 18 mo period of this study, mortality peaks associated with clinical AGD were only recorded during the first 12 mo of the marine phase of the production cycle. The initial AGD outbreak resulted in peak mortality in Week 17, which was preceded by PCR detections from Week 13 onwards. Freshwater treatments were an effective method for controlling the disease, resulting in a reduction in the weekly mortality levels and also a reduction in the number of PCR-positive fish. In comparison to traditional diagnostic methods, our PCR assay proved to be highly sensitive and a valuable tool to monitor disease progression and, therefore, has the potential to provide information on the timing and effectiveness of treatments.
    • Modelling origin and spread of Infectious Pancreatic Necrosis Virus in the Irish salmon farming industry: the role of inputs

      Ruane, N.M.; Murray, A.G.; Geoghegan, F.; Raynard, R.S. (Elsevier, 2009)
      Observed emergence of IPNV in farmed Irish salmon is simulated using a model originally developed to analyse the spread of the virus in Scotland [Murray, A.G., 2006a. A model of the spread of infectious pancreatic necrosis virus in Scottish salmon farms 1996–2003. Ecol. Model. 199, 64–72]. IPNV appears to have become established relatively recently in Ireland and the model is altered to explicitly simulate the origin of the spread of the virus. Input to freshwater farms was key to initiation of infection, but modelling suggests that endogenous spread was responsible for much of the subsequent increase in prevalence of IPNV. From the modelling, it is unlikely that direct imports accounted for most IPNV cases. If this is the case, cessation of imports, without a substantial improvement in biosecurity, would be likely to be of only limited effect in controlling IPNV. Marine IPNV prevalence appears to be insensitive to direct interventions in the marine environment (as in the Scottish model). A multi-element control strategy, targeting both endogenous spread and external input of infection and prioritising freshwater sites, but extending to marine sites, would probably now be required to eradicate IPNV from Ireland.
    • An outbreak of francisellosis in wild-caught Celtic Sea Atlantic cod, Gadus morhua L., juveniles reared in captivity

      Ruane, N.M.; Bolton-Warberg, M.; Rodger, H.D.; Colquhoun, D.J.; Geary, M.; McCleary, S.J.; O´Halloran, K.; Maher, K.; O´Keeffe, D.; Mirimin, L.; et al. (Wiley, 2013)
    • Phylogenetic analysis of infectious pancreatic necrosis virus in Ireland reveals the spread of a virulent genogroup 5 subtype previously associated with imports

      Ruane, N.M.; McCleary, S.J.; McCarthy, L.J.; Henshilwood, K. (Springer Verlag, 2015)
      Infectious pancreatic necrosis is a significant disease of farmed salmonids resulting in direct economic losses due to high mortality and disease-management costs. Significant outbreaks of the disease occurred in farmed Atlantic salmon in Ireland between 2003 and 2007, associated with imported ova and smolts. As the virus was known to occur in the country since the development of aquaculture in the 1980s, this study examined archived samples to determine whether these older isolates were associated with virulent forms. The study showed that two genotypes of IPNV were present in the 1990s, genotype 3 and genotype 5. A more virulent subtype of the virus first appeared in 2003 associated with clinical outbreaks of IPN, and this subtype is now the most prevalent form of IPNV found in the country. The data also indicated that IPNV in Ireland is more closely related to Scottish and continental European isolates than to Norwegian, Chilean and Australasian genogroup 5 isolates.