Ostreid herpesvirus OsHV-1 µVar in Pacific oysters Crassostrea gigas (Thunberg 1793) of the Wadden Sea, a UNESCO world heritage site.

The Wadden Sea is an extensive wetland area, recognized as UNESCO world heritage site of international importance. Since the mid-1990s, the invasive Pacific oyster Crassostrea gigas (Thunberg 1793) population in the area has grown exponentially, having a distinct impact on the ecosystem. The recent spread of the emerging oyster pathogen Ostreid herpesvirus OsHV-1 µVar worldwide and specifically in the oyster culture areas in the south of the Netherlands raised the question whether the virus may also be present in the Wadden Sea. In the summer of 2012 juvenile Pacific oysters were collected from five locations in the Dutch Wadden Sea. The virus was shown to be present in three of the five locations by real-time PCR and sequencing. It was concluded that OsHV-1 µVar has settled itself in Pacific oyster reefs in the Wadden Sea. These results and the recent discoveries of OsHV-1 microvariants in Australia and Korea indicate that OsHV-1 µVar and related variants might be more widespread than can be deduced from current literature. In particular in regions with no commercial oyster culture, similar to the Wadden Sea, the virus may go undetected as wild beds with mixed age classes hamper the detection of mortality among juvenile oysters.

Development and validation of a real-time PCR assay for the detection of anguillid herpesvirus 1.

Anguillid herpesvirus 1 (AngHV1) causes a haemorrhagic disease with increased mortality in wild and farmed European eel, Anguilla anguilla (L.) and Japanese eel Anguilla japonica, Temminck & Schlegel). Detection of AngHV1 is currently based on virus isolation in cell culture, antibody-based typing assays or conventional PCR. We developed, optimized and concisely validated a diagnostic TaqMan probe based real-time PCR assay for the detection of AngHV1. The primers and probe target AngHV1 open reading frame 57, encoding the capsid protease and scaffold protein. Compared to conventional PCR, the developed real-time PCR is faster, less labour-intensive and has a reduced risk of cross-contamination. The real-time PCR assay was shown to be analytically sensitive and specific and has a high repeatability, efficiency and r(2) -value. The diagnostic performance of the assay was determined by testing 10% w/v organ suspensions and virus cultures from wild and farmed European eels from the Netherlands by conventional and real-time PCR. The developed real-time PCR assay is a useful tool for the rapid and sensitive detection of AngHV1 in 10% w/v organ suspensions from wild and farmed European eels.

First evidence of infectious hematopoietic necrosis virus (IHNV) in the Netherlands.

In spring 2008, infectious hematopoietic necrosis virus (IHNV) was detected for the first time in the Netherlands. The virus was isolated from rainbow trout, Oncorhynchus mykiss (Walbaum), from a put-and-take fishery with angling ponds. IHNV is the causative agent of a serious fish disease, infectious hematopoietic necrosis (IHN). From 2008 to 2011, we diagnosed eight IHNV infections in rainbow trout originating from six put-and-take fisheries (symptomatic and asymptomatic fish), and four IHNV infections from three rainbow trout farms (of which two were co-infected by infectious pancreatic necrosis virus, IPNV), at water temperatures between 5 and 15 °C. At least one farm delivered trout to four of these eight IHNV-positive farms. Mortalities related to IHNV were mostly <40%, but increased to nearly 100% in case of IHNV and IPNV co-infection. Subsequent phylogenetic analysis revealed that these 12 isolates clustered into two different monophyletic groups within the European IHNV genogroup E. One of these two groups indicates a virus-introduction event by a German trout import, whereas the second group indicates that IHNV was already (several years) in the Netherlands before its discovery in 2008.

Survey of the crayfish plague pathogen presence in the Netherlands reveals a new Aphanomyces astaci carrier.

North American crayfish species as hosts for the crayfish plague pathogen Aphanomyces astaci contribute to the decline of native European crayfish populations. At least six American crayfish species have been reported in the Netherlands but the presence of this pathogenic oomycete with substantial conservational impact has not yet been confirmed in the country. We evaluated A. astaci prevalence in Dutch populations of six alien crustaceans using species-specific quantitative PCR. These included three confirmed crayfish carriers (Orconectes limosus, Pacifastacus leniusculus, Procambarus clarkii), two recently introduced but yet unstudied crayfish (Orconectes cf. virilis, Procambarus cf. acutus), and a catadromous crab Eriocheir sinensis. Moderate levels of infection were observed in some populations of O. limosus and P. leniusculus. Positive results were also obtained for E. sinensis and two Dutch populations of O. cf. virilis. English population of the latter species was also found infected, confirming this taxon as another A. astaci carrier in European waters. In contrast, Dutch P. clarkii seem only sporadically infected, and the pathogen was not yet detected in P. cf. acutus. Our study is the first confirmation of crayfish plague infections in the Netherlands and demonstrates substantial variation in A. astaci prevalence among potential hosts within a single region, a pattern possibly linked to their introduction history and coexistence.

Ultrastructural comparison of Bonamia spp. (Haplosporidia) infecting ostreid oysters.

The ultrastructure of Bonamia from Ostrea angasi from Australia, Crassostrea ariakensis from the USA, O. puelchana from Argentina and O. edulis from Spain was compared with described Bonamia spp. All appear conspecific with B. exitiosa. The Bonamia sp. from Chile had similarities to the type B. exitiosa from New Zealand (NZ), but less so than the other forms recognized as B. exitiosa. Two groups of ultrastructural features were identified; those associated with metabolism (mitochondrial profiles, lipid droplets and endoplasmic reticulum), and those associated with haplosporogenesis (Golgi, indentations in the nuclear surface, the putative trans-Golgi network, perinuclear granular material and haplosporosome-like bodies). Metabolic features were regarded as having little taxonomic value, and as the process of haplosporogenesis is not understood, only haplosporosome shape and size may be of taxonomic value. However, the uni-nucleate stages of spore-forming haplosporidians are poorly known and may be confused with Bonamia spp. uni-nucleate stages. The many forms of NZ B. exitiosa have not been observed in other hosts, which may indicate that it has a plastic life cycle. Although there are similarities between NZ B. exitiosa and Chilean Bonamia in the development of a larger uni-nucleate stage and the occurrence of cylindrical confronting cisternae, the clarification of the identity of Chilean Bonamia must await molecular studies.

Vibrio vulnificus outbreaks in Dutch eel farms since 1996: strain diversity and impact.

Vibrio vulnificus is a potentially zoonotic bacterial pathogen of fish, which can infect humans (causing necrotic fasciitis). We analysed 24 V. vulnificus isolates (from 23 severe eel disease outbreaks in 8 Dutch eel farms during 1996 to 2009, and 1 clinical strain from an eel farmer) for genetic correlation and zoonotic potential. Strains were typed using biotyping and molecular typing by high-throughput multilocus sequence typing (hiMLST) and REP-PCR (Diversilab®). We identified 19 strains of biotype 1 and 5 of biotype 2 (4 from eels, 1 from the eel farmer), that were subdivided into 8 MLST types (ST) according to the international standard method. This is the first report of V. vulnificus biotype 1 outbreaks in Dutch eel farms. Seven of the 8 STs, of unknown zoonotic potential, were newly identified and were deposited in the MLST database. The REP-PCR and the MLST were highly concordant, indicating that the REP-PCR is a useful alternative for MLST. The strains isolated from the farmer and his eels were ST 112, a known potential zoonotic strain. Antimicrobial resistance to cefoxitin was found in most of the V. vulnificus strains, and an increasing resistance to quinolones, trimethoprim + sulphonamide and tetracycline was found over time in strain ST 140. Virulence testing of isolates from diseased eels is recommended, and medical practitioners should be informed about the potential risk of zoonotic infections by V. vulnificus from eels for the prevention of infection especially among high-risk individuals. Additional use of molecular typing methods such as hiMLST and Diversilab® is recommended for epidemiological purposes during V. vulnificus outbreaks.

The occurrence of haplosporidian parasites, Haplosporidium nelsoni and Haplosporidium sp., in oysters in Ireland.

The phylum Haplosporidia is a group of obligate protozoan parasites that infect a number of freshwater and marine invertebrates. Haplosporidian parasites have caused significant mortalities in commercially important shellfish species worldwide. In this study, haplosporidia were detected in Pacific oysters Crassostrea gigas originating in Ireland and were subsequently identified independently in laboratories both in Ireland and in Spain as Haplosporidium nelsoni. In Ireland, H. nelsoni plasmodia were also observed in the heart tissue of a single Ostrea edulis. A range of techniques including heart smear screening, histology, standard polymerase chain reaction (PCR), direct sequencing and in situ hybridisation with an H. nelsoni specific DNA probe were carried out to confirm diagnosis. This is the first reporting of H. nelsoni in oysters in Ireland and this is the first reporting of the detection of this haplosporidian in O. edulis. In Ireland, another haplosporidian was also observed in a single O. edulis during heart smear screening. PCR and DNA sequencing were carried out and indicated the presence of a Haplosporidium sp., most likely Haplosporidium armoricanum. The low prevalence and intensity of infection of both haplosporidian species in Irish C. gigas and in particular O. edulis may indicate that their presence is inconsequential.

Tularaemia in a brown hare (Lepus europaeus) in 2013: first case in the Netherlands in 60 years.

Tularaemia has not been reported in Dutch wildlife since 1953. To enhance detection, as of July 2011, brown hares (Lepus europaeus) submitted for postmortem examination in the context of non-targeted wildlife disease surveillance, were routinely tested for tularaemia by polymerase chain reaction (PCR). Francisella tularensis subspecies holarctica infection was confirmed in a hare submitted in May 2013. The case occurred in Limburg, near the site of the 1953 case. Further surveillance should clarify the significance of this finding.

Bonamia exitiosa (Haplosporidia) observed infecting the European flat oyster Ostrea edulis cultured on the Spanish Mediterranean coast.

Bonamia exitiosa and Bonamia ostreae are parasites that reproduce within the haemocytes of several oyster species. In Europe, the host species is the flat oyster Ostrea edulis. The parasite B. ostreae has been responsible for mortalities since the late 1970s throughout the European Atlantic coast. B. exitiosa was first detected, in 2007, on this continent in flat oysters cultured in Galicia (NW Spain). Since then, the parasite has also been detected in France, Italy and the United Kingdom. The bays of the Ebro Delta in the south of Catalonia represent the main bivalve culture area in the Mediterranean coast of Spain. Previous information from the area includes reports of several flat oyster pathogens, including the notifiable parasite Marteilia refringens. However, the status with regard to Bonamia parasites was uncertain. In the present study, a Bonamia parasite was observed in flat oysters cultured in the Alfacs Bay of the Ebro Delta by histology and real-time PCR. PCR-RFLP and sequencing suggested the presence of B. exitiosa. Finally, phylogenetic analyses of the studied Bonamia isolates corroborated B. exitiosa infection. M. refringens was also observed in the same oyster batch, and co-infection with both parasites was also detected. This is the first detection of B. exitiosa, in Catalonia and the Spanish Mediterranean coast. The impact of the parasite on the Mediterranean flat oyster activity needs to be urgently addressed.

Inter-relationships of haplosporidians deduced from ultrastructural studies.

We reviewed papers reporting haplosporidian ultrastructure to compare inter-relationships based on ultrastructure with those based on molecular data, to identify features that may be important in haplosporidian taxonomy, and to consider parasite taxonomy in relation to host taxonomy. There were links between the following: (1) the plasmodia of an abalone parasite, Haplosporidium nelsoni and Urosporidium crescens in the release of haplosporosomes; (2) H. costale and H. armoricanum in haplosporosome shape and presence and shape of Golgi in spores; (3) basal asporous crustacean haplosporidians which form haplosporosomes from formative bodies (FBs) in vegetative stages--H. nelsoni, which forms haplosporosomes from FBs in plasmodial cytoplasm, and H. louisiana, Minchinia spp. and Bonamia perspora, which form haplosporosomes from FBs in spores; (4) crustacean haplosporidians, Bonamia spp. and M. occulta in the predominance of uni- and binucleate stages; and (5) lipid-like vesicles in sporoplasms of H. costale, H. armoricanum, H. lusitanicum, H. pickfordi, H. montforti, and B. perspora. In general, these relationships reflect phylogenies based on molecular studies. As well as spore form and ornamentation, haplosporogenesis in spores appears to be taxonomically important. Parasite and host taxonomy were linked in the infection of lower invertebrates by Urosporidium spp., the infection of oysters by Bonamia spp., and of molluscs by Minchinia spp. Haplosporidium spp. are patently an artificial, paraphyletic group probably comprising many taxa. Consequently, the taxonomy of haplosporidians needs a thorough revision.

Pooling of genital swabs for detection by PCR of Taylorella equigenitalis, the cause of contagious equine metritis.

BACKGROUND: Sets of genital swabs are routinely taken from horses to screen for the presence of Taylorella equigenitalis, the cause of contagious equine metritis. Typically, two to four different sites are swabbed at a time and tested by culture or PCR. OBJECTIVES: This study explored the feasibility of pooling these swabs for a single PCR test per animal instead of testing each swab individually. STUDY DESIGN: In vitro. METHODS: PCR signal strengths (Ct values) from 149 historical PCR positive genital swabs, together with historical data on the number of swabs in a set expected to be positive, were used to assess the suitability of pooling for screening horses for T. equigenitalis infection in the population at large. Twenty-four sets of four equine genital swabs were tested. The sets were prepared in the laboratory using one or more swabs positive for T. equigenitalis from naturally infected cases. Positive and negative swabs were selected to reflect a typical range of PCR Ct values expected in field cases of T. equigenitalis infection. These pools were tested by an established PCR to assess the impact and suitability of a PCR test on pooled swabs compared to individual swab testing, by comparing the Ct values. RESULTS: Pooling one positive swab with three negative swabs produced a small drop in Ct value but all pools were still clearly positive. MAIN LIMITATIONS: Large numbers of field positive horses are not available, but the proof of concept approach with laboratory prepared pools shows the method is applicable to field cases. CONCLUSIONS: It was concluded that pooling of swabs would confer no appreciable drop in the ability to detect a positive animal compared to individual swab testing; pooling is therefore a suitable alternative to individual swab testing with reduced costs. The Summary is available in Spanish - see Supporting Information.

High-resolution melting PCR analysis for rapid genotyping of Burkholderia mallei.

Burkholderia (B.) mallei is the causative agent of glanders. A previous work conducted on single-nucleotide polymorphisms (SNP) extracted from the whole genome sequences of 45 B. mallei isolates identified 3 lineages for this species. In this study, we designed a high-resolution melting (HRM) method for the screening of 15 phylogenetically informative SNPs within the genome of B. mallei that subtype the species into 3 lineages and 12 branches/sub-branches/groups. The present results demonstrate that SNP-based genotyping represent an interesting approach for the molecular epidemiology analysis of B. mallei.

Ultrastructure of sporulation in Haplosporidium armoricanum.

An ultrastructural study was carried out on the tissues of an oyster (Ostrea edulis), heavily infected with Haplosporidium armoricanum, that had been fixed in Carson's fixative. The well-fixed tissues revealed details of sporulation and of the spores, which had not been previously reported from H. armoricanum. These include the initial presence of sparse haplosporosomes after thickening of the plasma membrane in early sporonts, division of sporont nuclei by multiple fission, cup-like indentations in the nuclear surface associated with putative nuclear material in both the sporonts and spores, and cytoplasmic multi-vesicular bodies in the cytoplasm of sporonts and spores. The spore wall and operculum were formed from a light matrix that occurred in short cisternae of smooth endoplasmic reticulum in the episporoplasm, and parallel bundles of microfibrils were present in some spores. Spores were rarely bi-nucleate with the nuclei occurring as a diplokaryon, with putative nuclear material at the junction of the 2 nuclei. Nuclear membrane-bound Golgi (NM-BG) cisternae were common in spores, and they appeared to synthesise a light granular material into lysosome-like granules. Dense bodies similar to those reported from H. lusitanicum, H. pickfordi and H. monforti occurred in, or outside, the peripheral endosporoplasm, which was closely apposed to the spore wall. Spore haplosporosomes were frequently axehead-shaped, more like those of H. costale than those previously reported from H. armoricanum, and in some haplosporosomes there was a small round lucent patch with a dark point near the centre of the lucent patch. Overall, H. armoricanum appears to be closely related to H. costale and Bonamia spp. Although the endosporoplasm of H. armoricanum has NM-BG and it resembles the uni-nucleate stage, it appears to be unlikely that they are the same, as the axehead-shaped haplosporosomes of the spore differ considerably from the spherical haplosporosomes of vegetative stages.

Regulation of interleukin 1 beta RNA expression in the common carp, Cyprinus carpio L.

The intron-exon organisation of the carp IL-1beta gene consists of 2455bp and comprises seven exons. Three IL-1beta RNA transcripts have been found in carp: (1) a fully spliced product; (2) exon 1-7 with introns 5 and 6; and (3) exon 1-7 with intron 5 only. The intron-containing products probably represent partially spliced transcripts. IL-1beta mRNA expression in carp was semi-quantitatively analysed by RT-PCR in multiple organs, including brain and pituitary. Constitutive expression of the IL-1beta mRNA was found in these organs with a predominant expression in the immune organs head kidney and spleen. Furthermore, a scattered distribution of IL-1beta producing cells was shown by in situ hybridisations of head kidney tissue. Administration of phorbol-myristate-acetate (PMA), lipopolysaccharide (LPS) or retinoic acid (RA), to phagocytes isolated from the head kidney, resulted in expression of IL-1beta intron-containing transcripts. Of these, only PMA and LPS were stimulators that induced the fully spliced transcript. A role for the nuclear factor (NF)-kappaB pathway in carp IL-1beta expression was shown with suppression of the LPS-induced IL-1beta expression by NF-kappaB inhibitor pyrrolidine dithiocarbamate (PDTC). Cortisol was able to inhibit in vitro constitutive expression of IL-1beta transcripts. Addition of cortisol simultaneously with LPS could not substantially inhibit transcription.

Subtypes of HLA-B27 detected by cytotoxic T lymphocytes and their role in self-recognition.

In the present study cytotoxic T lymphocytes were generated in MLC of lymphocytes from two unrelated HLA-A, B, C-identical, B27-positive, but D/DR-different, individuals. These CTL were shown to detect subtypes of HLA-B27. CTL specific for influenza virus lysed infected target cells matched for HLA-B27 only when they shared the same subtype. This indicates that the two subtypes of HLA-B27 detected by CTL function also as distinct elements in a self-restricted CTL response. Both subtypes were found among patients with ankylosing spondylitis.

Indications for a distinct putative T cell population in mucosal tissue of carp (Cyprinus carpio L.).

A monoclonal antibody against carp intestinal T cells (WCL38; of IgM class) was produced by immunization of mice with isolated membrane molecules of carp intestinal intraepithelial lymphoid cells. Flow cytometric analysis showed that WCL38 reacted with 50-70% of the lymphoid cells isolated from intestine, gills or skin, with less than 6% of lymphoid cells isolated from thymus, head kidney or spleen and with a negligible number of PBL. WCL38+ cells were abundant in the intestinal epithelium and less numerous in the lamina propria. Immunogold labelling confirmed that WCL38 reacted with lymphoid cells; in gills and skin some of them have the morphology of large granular lymphoid cells. Immunochemical analysis showed that WCL38 reacted with dimeric membrane molecule on mucosal lymphoid cells with an Mr of 76 kDa, consisting of two 38 kDa subunits. WCL 38+ lymphoid cells are postulated to T cells, since WCL38 does not react with B cells, macrophages or non-specific cytotoxic cells. In conclusion, like higher vertebrates, carp seem to have a distinct (Putative) T cell population in their mucosal tissues.

Induction of oral tolerance in carp (Cyprinus carpio L.) after feeding protein antigens.

Induction of oral tolerance against ferritin, recombinant surface glycoprotein of viral haemorrhagic septicemia virus (KLG18) and ovalbumin (OVA) was studied in carp. Feeding of ferritin or KLG18 resulted in lower Ab titres compared to unprimed controls when animals were intramuscularly (i.m.) injected with protein 10 weeks later and sampled 21 days after this injection. After administration of OVA by different routes (oral, anal, i.m.) and i.m. injection with OVA + Freund's incomplete adjuvant 2 months later, only a few fish responded to OVA as measured by serum Ab titres. Responsiveness to OVA appeared to be carp strain dependent. When an isogenic carp strain was selected for an optimal response to i.m. injection with OVA, this carp strain did not develop oral tolerance after feeding. In contrast, 6 x feeding high doses of OVA on subsequent days, resulted in immunological memory formation. Oral tolerance can be induced in carp, but differences in tolerance induction may depend on the protein used. A possible role of genetic factors in the induction of oral tolerance in fish is discussed.

Differentiation between Cyprinid herpesvirus type-3 lineages using duplex PCR.

To date, all the isolates of Cyprinid herpesvirus type-3 (CyHV3) responsible for serious outbreaks in carps Cyprinus carpio have been found to be very similar or identical on the basis of DNA sequences of a few reference genes. However, two genetic lineages (U/I and J) are distinguished by full-length genome sequencing. Two molecular markers presenting genetic variations were targeted for developing a duplex PCR assay able to distinguish CyHV3-U/I from CyHV3-J while avoiding DNA sequencing. The method was validated on a series of 42 samples of infected carps from France, The Netherlands and Poland collected from 2001 to 2008. Among these samples, both the U/I and J genotypes were identified, but also a third genotype representing a genetic intermediate between U/I and J for one of the two molecular markers. A classification of CyHV3 genotypes, based on the alleles of the two molecular markers, is proposed. The assay is easy to perform and provides a genotype information with samples moderately or highly concentrated. This tool should improve our knowledge regarding the present distribution and future diversification of this emerging virus.

Selective determination of trace levels of phenol in river water using electrochemical concentration modulation correlation chromatography.

Electrochemical concentration modulation (ECM) was used as a sample introduction technique in the correlation chromatographic (CC) trace determination of phenol in water. The linearity and sensitivity of the method were tested and detection limits were calculated. The selectivity of the technique was confirmed by comparison with loop injection experiments using several detection methods. In preliminary experiments is was found that ECM-CC, in combination with fluorescence detection, is selective and sensitive enough to be used for the monitoring of the phenol concentration in river water at the draining points for drinking water production.