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Dis Aquat Organ [journal]
- Distribution and epidemiology of genotypes of the crayfish plague agent Aphanomyces astaci from noble crayfish Astacus astacus in Finland. [Journal Article]
- Dis Aquat Organ 2013 Apr 11; 103(3):199-208.
The crayfish plague agent Aphanomyces astaci was isolated from 69 noble crayfish Astacus astacus samples in Finland between 1996 and 2006. All isolates were genotyped using randomly amplified polymorphic DNA-polymerase chain reaction (RAPD-PCR). Altogether, 43 isolates belonged to the genotype group of Astacus strains (As), which is assumed to represent the genotype originally introduced into Europe around 1860 and into Finland in 1893. There were 26 crayfish plague isolates belonging to the group of Pacifastacus strain I (Ps1), which appeared in Europe after the stocking of the North American species signal crayfish Pacifastacus leniusculus. The geographical distribution of the 2 genotypes in Finland corresponded with the stocking strategies of signal crayfish. The majority of Ps1-strains (83%) were associated with a classical crayfish plague episode involving acute mortality, compared with only 33% of the As-strains. As-strains were found more often by searching for reasons for population declines or permanently weak populations, or through cage experiments in connection with reintroduction programmes. In some water bodies, isolations of the As-strains were made in successive years. This study shows that persistent crayfish plague infection is not uncommon in noble crayfish populations. The described epidemiological features suggest a difference in virulence between these 2 genotypes.
- Laboratory tests of antifungal agents to treat tadpoles against the pathogen Batrachochytrium dendrobatidis . [Journal Article]
- Dis Aquat Organ 2013 Apr 11; 103(3):191-7.
The fungus Batrachochytrium dendrobatidis (Bd), which is the etiological agent of the disease chytridiomycosis, is threatening both wild and captive amphibians. While there are some methods of treating amphibians in captivity, no method has yet been shown to be a promising treatment for amphibian populations in natural habitats. Here we present the results of a laboratory experiment in which we tested 2 antifungal agents that might be used to treat amphibians in the field. As a first step towards the goal of developing mitigation methods, we tested the efficiency of these agents in reducing Bd prevalence and loads (zoospore counts) in the laboratory. We exposed naturally infected tadpoles of the midwife toad Alytes obstetricans to different concentrations of the antifungal agents for 7 d. We found that Virkon Aquatic® affected neither Bd prevalence nor loads. At 0.625 ml l-1 of General Tonic®, prevalence was reduced to 60%, and infected animals had greatly reduced burdens. However, tadpole length was reduced by 19% and mass by 32% on average compared to the control group, suggesting a negative effect on fitness. Tadpole survival was not affected at 0.625 ml l-1 or 1.25 ml l-1, but was reduced to 60% at 2.5 ml l-1. Keeping animals in a dilution of General Tonic® for 7 d at a concentration of 0.625 ml l-1 might be an easy way to reduce zoospore counts in large numbers of animals at relatively low cost.
- Ranavirus infection in a group of wild-caught Lake Urmia newts Neurergus crocatus imported from Iraq into Germany. [Journal Article]
- Dis Aquat Organ 2013 Apr 11; 103(3):185-9.
High mortality, in association with anorexia and skin ulcerations, occurred in a group of wild-caught Lake Urmia newts Neurergus crocatus, imported from Iraq in 2011. Predominant findings in the pathological examinations consisted of systemic hemorrhages and ulcerative dermatitis. Ranavirus DNA was detected via PCR in 2 of 3 dead animals, and a part of the major capsid protein (MCP) gene was sequenced. The analyzed portion of the MCP gene was 99% identical to the corresponding portion of the frog virus 3 genome. This is the first description of a ranavirus in Lake Urmia newts and in wild-caught amphibians from Iraq, as well as the first description of ranavirus infection in a urodele from the Middle East.
- Susceptibility of the European common frog Rana temporaria to a panel of ranavirus isolates from fish and amphibian hosts. [Journal Article]
- Dis Aquat Organ 2013 Apr 11; 103(3):171-83.
Ranaviruses are an emerging group of viruses and have been implicated in an increase of epidemics in susceptible species. They have a wide host range, infecting fish, amphibians and reptiles, with some isolates able to infect multiple species from different animal classes. Whilst some information exists on the pathogenicity of ranaviruses to novel hosts, there is none on the pathogenicity of fish ranaviruses to amphibians; this information is needed to develop measures to prevent the further spread of ranaviral disease in the aquatic environment. We undertook bath infection trials to assess the susceptibility of the European common frog Rana temporaria to 9 ranavirus isolates comprising doctor fish virus (DFV), European sheatfish virus (ESV), epizootic haematopoietic necrosis virus (EHNV), guppy virus 6 (GV6), pike-perch iridovirus (PPIV) and short-finned eel ranavirus (SERV) from fish hosts, and Bohle iridovirus (BIV), frog virus 3 (FV3) and Rana esculenta virus 282/I02 (REV) from amphibians. Animals were challenged as tadpoles at 15 and 20°C and as recent metamorphs at room temperature (20 ± 1°C) to investigate the effect of temperature and amphibian developmental stage on virus pathogenicity. Tadpoles were susceptible to FV3, PPIV and REV, but refractory to the other ranaviruses. Post-metamorphs were susceptible to FV3 and REV but refractory to BIV (the other ranaviruses were not tested). Significant mortality occurred in post-metamorphs and in tadpoles challenged at 20°C but was low in tadpoles challenged at 15°C. This study presents the first evidence of mortality in an amphibian species after challenge with ranavirus originally isolated from fish.
- Aphanomyces astaci in wild crayfish populations in Slovenia: first report of persistent infection in a stone crayfish Austropotamobius torrentium population. [Journal Article]
- Dis Aquat Organ 2013 Mar 26; 103(2):157-69.
All 5 crayfish species inhabiting Slovenian freshwaters, of which 3 are indigenous crayfish species (ICS: Astacus astacus, Austropotamobius pallipes, and A. torrentium) and 2 are non-indigenous (NICS: Pacifastacus leniusculus and Cherax quadricarinatus), were inspected for the presence of Aphanomyces astaci, the causative agent of crayfish plague. Wild crayfish populations showing no clinical signs of infection were inspected using A. astaci-specific real-time PCR. In addition, a conventional PCR assay was employed and confirmative sequencing was performed. Out of 88 analyzed crayfish, 15/27 (55.6%) specimens of A. torrentium from Borovnišcˇ%%KERN_ERR%%ica Brook and 4/35 (11.4%) of P. leniusculus from the Mura River tested positive, showing low to moderate levels of infection (agent levels A1-A4 and A1-A3, respectively). Results revealed the presence of A. astaci not only in the resistant NICS but also in ICS, since the infected population of A. torrentium presumably had no contact with the NICS carrier and appeared to sustain A. astaci infection in the 2 sampling years. Although the A. astaci genotype has not yet been identified, a connection between the latent infection in ICS and a Group A strain of A. astaci, co-evolving with A. torrentium since its first introduction to Slovenia, is suggested as the most plausible conclusion. This is the first reported population of the genus Austropotamobius with persistent infection, in addition to the already known populations of the genus Astacus. Findings of the presumed co-evolution of A. astaci and ICS hosts open new perspectives, necessitating additional studies on the presence of A. astaci genotypes in the persistently infected ICS populations.
- Self-limiting outbreak of crayfish plague in an Austropotamobius pallipes population of a river basin in the Abruzzi region (central Italy). [Journal Article]
- Dis Aquat Organ 2013 Mar 26; 103(2):149-56.
Crayfish plague, caused by the oomycete Aphanomyces astaci, is a serious disease of European freshwater crayfish and has eliminated entire populations in several European countries. In September 2011, mortality was observed among the Austropotamobius pallipes population of a river basin in the Abruzzi region (central Italy), and A. astaci DNA was detected by PCR in dead crayfish. A systematic survey was carried out to evaluate the spread and the effects of the plague in the river basin. The source of the outbreak remained unknown since North American crayfish species, which frequently act as subclinical carriers of the infection, were not detected in the area. The A. pallipes population disappeared from a river stretch of ~1 km, where A. astaci infection was detected in dead crayfish. However, apparently unaffected crayfish were still present upstream of that area as well as in a tributary that joined the brook in the apparently depopulated stretch. A. astaci infection was not detected in dead individuals collected in the upstream area and tributary. A follow-up visit conducted in the following season showed the presence of A. pallipes in the river stretch hit by the plague. In this outbreak, the spread of the infection could have been limited by a low density of the crayfish population and by the geographic conformation of the river basin, which includes a dense network of small tributaries, characterized by high flow velocity and low water temperature. In this particular setting, crayfish plague outbreaks can remain undetected. This underlines the importance of active monitoring programs aimed at the prompt recognition of both episodes of mortality and the presence of non-indigenous crayfish species.
- Culture-independent analysis of bacterial communities in hemolymph of American lobsters with epizootic shell disease. [Journal Article]
- Dis Aquat Organ 2013 Mar 26; 103(2):141-8.
Epizootic shell disease (ESD) of the American lobster Homarus americanus H. Milne Edwards, 1837 is a disease of the carapace that presents grossly as large, melanized, irregularly shaped lesions, making the lobsters virtually unmarketable because of their grotesque appearance. We analyzed the bacterial communities present in the hemolymph of lobsters with and without ESD using nested-PCR of the 16S rRNA genes followed by denaturing gradient gel electrophoresis. All lobsters tested (n = 42) had bacterial communities in their hemolymph, and the community profiles were highly similar regardless of the sampling location or disease state. A number of bacteria were detected in a high proportion of samples and from numerous locations, including a Sediminibacterium sp. closely related to a symbiont of Tetraponera ants (38/42) and a Ralstonia sp. (27/42). Other bacteria commonly encountered included various Bacteroidetes, Pelomonas aquatica, and a Novosphingobium sp. One bacterium, a different Sediminibacterium sp., was detected in 20% of diseased animals (n = 29), but not in the lobsters without signs of ESD (n = 13). The bacteria in hemolymph were not the same as those known to be present in lesion communities except for the detection of a Thalassobius sp. in 1 individual. This work demonstrates that hemolymph bacteremia and the particular bacterial species present do not correlate with the incidence of ESD, providing further evidence that microbiologically, ESD is a strictly cuticular disease. Furthermore, the high incidence of the same species of bacteria in hemolymph of lobsters may indicate that they have a positive role in lobster fitness, rather than in disease, and further investigation of the role of bacteria in lobster hemolymph is required.
- Identification and characterization of Vibrio harveyi associated with diseased abalone Haliotis diversicolor. [Journal Article]
- Dis Aquat Organ 2013 Mar 26; 103(2):133-9.
Mass mortality of farmed small abalone Haliotis diversicolor occurred in Fujian, China, from 2009 to 2011. Among isolates obtained from moribund abalones, the dominant species AP37 exhibited the strongest virulence. After immersion challenge with 106 CFU ml-1 of AP37, abalone mortalities of 0, 53 and 67% were induced at water temperatures of 20°C, 24°C, and 28°C, respectively. Following intramuscular injection, AP37 showed a low LD50 (median lethal concentration) value of 2.9 × 102 CFU g-1 (colony forming units per gram abalone wet body weight). The LT50 (median lethal time) values were 5.2 h for 1 × 106 CFU abalone-1, 8.4 h for 1 × 105 CFU abalone-1, and 21.5 h for 1 × 104 CFU abalone-1. For further analysis of virulence, AP37 was screened for the production of extracellular factors. The results showed that various factors including presence of flagella and production of extracellular enzymes, such as lipase, phospholipase and haemolysin, could be responsible for pathogenesis. Based on its 16S rRNA gene sequence, strain AP37 showed >98.8% similarity to Vibrio harveyi, V. campbellii, V. parahaemolyticus, V. alginolyticus, V. natriegens and V. rotiferianus, so it could not be identified by this method. However, multi-locus sequence analysis (MLSA) of concatenated sequences, including the rpoD, rctB, gyrB, toxR and pyrH genes, identified strain AP37 as V. harveyi. Phenotypic characters of AP37 were identified by API 20E. In antibiotic susceptibility tests, strain AP37 exhibited susceptibility to 7 antibiotics and resistance to 13. This is the first report of a V. harveyi-related species being linked with the mass mortality of adult abalone H. diversicolor in southern China.
- Involvement of the cell-specific pigment genes pks and sult in bacterial defense response of sea urchins Strongylocentrotus intermedius. [Journal Article]
- Dis Aquat Organ 2013 Mar 26; 103(2):121-32.
Bacterial infections are one of the most important problems in mass aquaculture, causing the loss of millions of juvenile organisms. We isolated 22 bacterial strains from the cavity fluid of the sea urchin Strongylocentrotus pallidus and used phylogenetic analysis based on 16S rRNA gene sequences to separate the bacterial strains into 9 genera (Aliivibrio, Bizionia, Colwellia, Olleya, Paenibacillus, Photobacterium, Pseudoalteromonas, Shewanella, and Vibrio). Incubating Strongylocentrotus intermedius larvae with a strain from each of the 9 bacterial genera, we investigated the viability of the larvae, the amount of pigment cells, and the level of polyketide synthase (pks) and sulfotransferase (sult) gene expression. Results of the assay on sea urchin development showed that all bacterial strains, except Pseudoalteromonas and Bizionia, suppressed sea urchin development (resulting in retardation of the embryos' development with cellular disorders) and reduced cell viability. We found that pks expression in the sea urchin larvae after incubation with the bacteria of 9 tested genera was significantly increased, while the sult expression was increased only after the treatment with Pseudoalteromonas and Shewanella. Shikimic acid, which is known to activate the biosynthesis of naphthoquinone pigments, increased the tolerance of the sea urchin embryos to the bacteria. In conclusion, we show that the cell-specific pigment genes pks and sult are involved in the bacterial defense response of sea urchins.
- Structure of Flavobacterium psychrophilum populations infecting farmed rainbow trout Oncorhynchus mykiss . [Journal Article]
- Dis Aquat Organ 2013 Mar 26; 103(2):111-9.
Flavobacterium psychrophilum isolated from rainbow trout Oncorhynchus mykiss suffering from bacterial cold-water disease (BCWD) can dissociate into 2 morphological colony types, rough (R) and smooth (S). However, the presence of the 2 morphotypes in disease outbreaks has not yet been investigated thoroughly. We examined the occurrence of R and S morphotypes in rainbow trout from BCWD outbreaks and in unfertilized eggs from a hatchery. The isolated colony types were characterized by pulsed field gel electrophoresis (PFGE), plasmid analysis, and oxolinic acid susceptibility testing. From most outbreaks, both morphotypes were isolated, although the S type only was isolated from the majority of individual fish. PFGE analysis showed both diverse and indistinguishable genetic patterns among the concurrent morphotypes. While PFGE patterns common to both fish and egg isolates were identified, this was not always the case. Resistant and sensitive isolates of both colony types were isolated from individual disease outbreaks. The plasmid pattern was partly associated with the colony type, showing identical or completely different patterns for the R and S types isolated from the same outbreak. The study showed that within a BCWD outbreak, F. psychrophilum cells with different morphology, plasmid content, antibiotic susceptibility, and PFGE pattern can be isolated, suggesting that F. psychrophilum populations infecting rainbow trout in farm environments can be diverse and thus complicate the control of the disease.