Climate change influences on marine infectious diseases: implications for management and society

Infectious diseases are common in marine environments, but the effects of a changing climate on marine pathogens are not well understood. Here we review current knowledge about how the climate drives host-pathogen interactions and infectious disease outbreaks. Climate-related impacts on marine diseases are being documented in corals, shellfish, finfish, and humans; these impacts are less clearly linked for other organisms. Oceans and people are inextricably linked, and marine diseases can both directly and indirectly affect human health, livelihoods, and well-being. We recommend an adaptive management approach to better increase the resilience of ocean systems vulnerable to marine diseases in a changing climate. Land-based management methods of quarantining, culling, and vaccinating are not successful in the ocean; therefore, forecasting conditions that lead to outbreaks and designing tools/approaches to influence these conditions may be the best way to manage marine disease.

Development and validation of a quantitative PCR assay for Ichthyophonus spp

Members of the genus Ichthyophonus are trophically transmitted, cosmopolitan parasites that affect numerous fish species worldwide. A quantitative PCR (qPCR) assay specific for genus Ichthyophonus 18S ribosomal DNA was developed for parasite detection and surveillance. The new assay was tested for precision, repeatability, reproducibility, and both analytical sensitivity and specificity. Diagnostic sensitivity and specificity were estimated using tissue samples from a wild population of walleye pollock Theragra chalcogramma. Ichthyophonus sp. presence in tissue samples was determined by qPCR, conventional PCR (cPCR), and histology. Parasite prevalence estimates varied depending upon the detection method employed and tissue type tested. qPCR identified the greatest number of Ichthyophonus sp.-positive cases when applied to walleye pollock skeletal muscle. The qPCR assay proved sensitive and specific for Ichthyophonus spp. DNA, but like cPCR, is only a proxy for infection. When compared to cPCR, qPCR possesses added benefits of parasite DNA quantification and a 100-fold increase in analytical sensitivity. Because this novel assay is specific for known members of the genus, it is likely appropriate for detecting Ichthyophonus spp. DNA in various hosts from multiple regions. However, species-level identification and isotype variability would require DNA sequencing. In addition to distribution and prevalence applications, this assay could be modified and adapted for use with zooplankton or environmental samples. Such applications could aid in investigating alternate routes of transmission and life history strategies typical to members of the genus Ichthyophonus.

Putative phage hyperparasite in the rickettsial pathogen of abalone, "Candidatus Xenohaliotis californiensis"

Studies on the ecology of microbial parasites and their hosts are predicated on understanding the assemblage of and relationship among the species present. Changes in organismal morphology and physiology can have profound effects on host-parasite interactions and associated microbial community structure. The marine rickettsial organism, "Candidatus Xenohaliotis californiensis" (WS-RLO), that causes withering syndrome of abalones has had a consistent morphology based on light and electron microscopy. However, a morphological variant of the WS-RLO has recently been observed infecting red abalone from California. We used light and electron microscopy, in situ hybridization and16S rDNA sequence analysis to compare the WS-RLO and the morphologically distinct RLO variant (RLOv). The WS-RLO forms oblong inclusions within the abalone posterior esophagus (PE) and digestive gland (DG) tissues that contain small rod-shaped bacteria; individual bacteria within the light purple inclusions upon hematoxylin and eosin staining cannot be discerned by light microscopy. Like the WS-RLO, the RLOv forms oblong inclusions in the PE and DG but contain large, pleomorphic bacteria that stain dark navy blue with hematoxylin and eosin. Transmission electron microscopy (TEM) examination revealed that the large pleomorphic bacteria within RLOv inclusions were infected with a spherical to icosahedral-shaped putative phage hyperparasite. TEM also revealed the presence of rod-shaped bacteria along the periphery of the RLOv inclusions that were morphologically indistinguishable from the WS-RLO. Binding of the WS-RLO-specific in situ hybridization probe to the RLOv inclusions demonstrated sequence similarity between these RLOs. In addition, sequence analysis revealed 98.9-99.4 % similarity between 16S rDNA sequences of the WS-RLO and RLOv. Collectively, these data suggest that both of these RLOs infecting California abalone are "Candidatus Xenohaliotis californiensis," and that the novel variant is infected by a putative phage hyperparasite that induced morphological variation of its RLO host.

Friend or foe: the association of Labyrinthulomycetes with the Caribbean sea fan Gorgonia ventalina

A new syndrome in sea fans Gorgonia ventalina consisting of multifocal purple spots (MFPS) has been observed in the Caribbean Sea. Surveys of MFPS on sea fans were conducted from 2006 to 2010 at a shallow and deep site in La Parguera, Puerto Rico (PR). At the shallow site, MFPS increased between 2006 and 2010 (site average ranged from 8 to 23%), with differences found at depths over time using an analysis of covariance (ANCOVA, p < 0.0001). As a potential causative agent we examined a Labyrinthulomycota-like ovoid parasite that was observed to be abundant in MFPS lesions in light micrographs. Labyrinhylomycetes were successfully isolated, cultured and characterized in sea fans from Florida and PR. Sequence information obtained from the small subunit (SSU) rRNA gene indicated that Labyrinthulomycetes in most sea fans (healthy and MFPS sea fans from Florida; MFPS from PR) and the cultured microorganism are in the genus Aplanochytrium, although some healthy sea fans from PR contained members of the genus Thraustochytrium. Both genera fall within the family Thraustochytriidae. Histology confirmed observations of thraustochytrids within apparently healthy and MFPS sea fans from PR, and specific staining indicated a host melanization response only in colonies containing Labyrinthulomycetes or fungal infections. Growth trials indicate that the temperature-growth optima for the cultured microorganism is ~30°C. In inoculation experiments, the cultured Aplanochytrium did not induce purple spots, and histology revealed that many of the apparently healthy recipients contained Labyrinthulomycetes prior to inoculation. Taken together, these results indicate that the Labyrinthulomycetes associated with sea fans is likely an opportunistic pathogen. Further studies are needed to understand the pathogenesis of this microorganism in sea fans and its relationship with MFPS.

Inability to demonstrate fish-to-fish transmission of Ichthyophonus from laboratory infected Pacific herring Clupea pallasii to naïve conspecifics

The parasite Ichthyophonus is enzootic in many marine fish populations of the northern Atlantic and Pacific Oceans. Forage fishes are a likely source of infection for higher trophic level predators; however, the processes that maintain Ichthyophonus in forage fish populations (primarily clupeids) are not well understood. Lack of an identified intermediate host has led to the convenient hypothesis that the parasite can be maintained within populations of schooling fishes by waterborne fish-to-fish transmission. To test this hypothesis we established Ichthyophonus infections in Age-1 and young-of-the-year (YOY) Pacific herring Clupea pallasii (Valenciennes) via intraperitoneal (IP) injection and cohabitated these donors with naïve conspecifics (sentinels) in the laboratory. IP injections established infection in 75 to 84% of donor herring, and this exposure led to clinical disease and mortality in the YOY cohort. However, after cohabitation for 113 d no infections were detected in naïve sentinels. These data do not preclude the possibility of fish-to-fish transmission, but they do suggest that other transmission processes are necessary to maintain Ichthyophonus in wild Pacific herring populations.

Development of a polymerase chain reaction for the detection of abalone herpesvirus infection based on the DNA polymerase gene

A 5781-base pair (bp) fragment of genomic DNA from the Taiwanese abalone herpesvirus was obtained and showed 99% (5767/5779) homology in the nucleotide sequence and 99% (1923/1926) in the amino acid sequence with the DNA polymerase gene of the abalone herpesvirus strain Victoria/AUS/2007. Homology of the amino acid sequence with the DNA polymerase of ostreid herpesvirus 1 was 30% (563/1856). In this study, a PCR-based procedure for detecting herpesvirus infection of abalone, Haliotis diversicolor supertexta, in Taiwan was developed. The method employed primer sets targeting the viral DNA polymerase gene, and was able to amplify DNA fragments of the expected size from infected samples. Primer sets of 40f and 146r were designed for amplification of an expected PCR product of 606 bp. Combining the new PCR protocol with histopathology, this assay can serve as a reliable diagnostic for herpesvirus infections in abalone.

Quantifying Ostreid herpesvirus (OsHV-1) genome copies and expression during transmission

Understanding the pathogenic potential of a new pathogen strain or a known pathogen in a new locale is crucial for management of disease in both wild and farmed animals. The Ostreid herpesvirus-1 (OsHV-1), a known pathogen of early-life-stage Pacific oysters, Crassostrea gigas, has been associated with mortalities of juvenile oysters in many locations around the world including Tomales Bay, California. In two trials, the California OsHV-1 strain was transmitted from infected juvenile C. gigas to naïve C. gigas larvae. Survival of control larvae was high throughout both trials (97-100%) and low among those exposed to OsHV-1. No OsHV-1-exposed larvae survived to day 9 in trial 1, while trial 2 was terminated at day 7 when survival was 36.90 ± 8.66%. To assess the amount of OsHV-1 DNA present, we employed quantitative polymerase chain reaction (qPCR) assays based on the A fragment and OsHV-1 catalytic subunit of a DNA polymerase δ (DNA pol) gene. Viral genome copy numbers based on qPCR assays peaked between 3 and 5 days. To measure the presence of viable and actively transcribing virus, the DNA pol gene qPCR assay was optimized for RNA analysis after being reverse transcribed (RT-qPCR). A decline in virus gene expression was measured using RT-qPCR: relative to earlier experimental time points copy numbers were significantly lower on day 9, trial 1 (p < 0.05) and day 7, trial 2 (p < 0.05). Peaks in copies of active virus per genome occurred during two periods in trial 1 (days 1 and 5/7, p < 0.05) and one period in trial 2 (day 1, p < 0.05). Transmission electron microscopy confirmed OsHV-1 infection; herpesvirus-like nucleocapsids, capsids, and extracellular particles were visualized. We demonstrated the ability to transmit OsHV-1 from infected juvenile oysters to naïve larvae, which indicates the spread of OsHV-1 between infected hosts in the field and between commercial farms is possible. We also developed an important tool (OsHV-1-specific RT-qPCR for an active virus gene) for use in monitoring for active virus in the field and in laboratory based transmission experiments.

Detection of the oyster herpesvirus in commercial bivalve in northern California, USA: conventional and quantitative PCR

The ostreid herpesvirus (OsHV-1) and related oyster herpesviruses (OsHV) are associated with world-wide mortalities of larval and juvenile bivalves. To quantify OsHV viral loads in mollusc tissues, we developed a SYBR Green quantitative PCR (qPCR) based on the A-region of the OsHV-1 genome. Reaction efficiency and precision were demonstrated using a plasmid standard curve. The analytical sensitivity is 1 copy per reaction. We collected Crassostrea gigas, C. sikamea, C. virginica, Ostrea edulis, O. lurida, Mytilus galloprovincialis, and Venerupis phillipinarum from Tomales Bay (TB), and C. gigas from Drakes Estero (DE), California, U.S.A., and initially used conventional PCR (cPCR) to test for presence of OsHV DNA. Subsequently, viral loads were quantified in selected samples of all tested bivalves except O. lurida. Copy numbers were low in each species tested but were significantly greater in C. gigas (p < 0.0001) compared to all other species, suggesting a higher level of infection. OsHV DNA was detected with cPCR and/or qPCR and confirmed by sequencing in C. gigas, C. sikamea, C. virginica, O. edulis, M. galloprovincialis, and V phillipinarum from TB and C. gigas from DE. These data indicate that multiple bivalve species may act as reservoirs for OsHV in TB. A lack of histological abnormalities in potential reservoirs requires alternative methods for their identification. Further investigation is needed to determine the host-parasite relationship for each potential reservoir, including characterization of viral loads and their relationship with infection (via in situ hybridization), assessments of mortality, and host responses.

Gene expression patterns of abalone, Haliotis tuberculata, during successive infections by the pathogen Vibrio harveyi

Since 1998, episodic mass mortality of the abalone Haliotistuberculata has been observed along the northern Brittany coast of France caused by a complex interaction among the host, pathogen and environmental factors. In the present study, abalone were submitted to two successive infections with the pathogen Vibrioharveyi under controlled conditions. During the first challenge, infection by V.harveyi resulted in 64% mortality of mature abalone. After a second infection of those surviving the first challenge, only 44% mortality was observed. Physiological variability in the host response appears to be a major determinant in susceptibility to V.harveyi. In order to isolate differentially expressed genes in H.tuberculata challenged with this bacterium, suppression subtractive hybridization (SSH) cDNA libraries were constructed from muscle of moribund abalone (susceptibles), surviving individuals (apparently resistant to the bacterium) and control (unexposed) animals. Of the 1152 clones sequenced, 218 different partial cDNA sequences were obtained and represented 69 known genes. Of these, 65 were identified for the first time in H.tuberculata. Using real-time PCR, a time-course study was conducted on 19 of the genes identified by SSH. A majority of differentially expressed transcripts were down-regulated in susceptible individuals as compared to their resistant counterparts. Bacterial challenge of abalone resulted in the up-regulation of three transcripts (encoding ferritin, heat shock protein HSP84 and fatty acid binding protein FABP) in those that survived exposure to V.harveyi. This study has identified potential candidates for further investigation into the functional basis of resistance and susceptibility to summer vibriosis outbreaks in abalone.

Withering syndrome in the abalone Haliotis diversicolor supertexta

Abalone aquaculture is a small but growing industry in Thailand and is based on both the exotic Haliotis diversicolor supertexta and the native H. asinina. Withering syndrome (WS) in abalone is caused by an infection with the Rickettsia-like organism (RLO) 'Candidatus Xenohaliotis californiensis' and has been spread to many countries globally. The present study reports the first observation of the WS-RLO agent in the small abalone, H. diversicolor supertexta in Thailand, Taiwan (ROC) and the People's Republic of China (PRC). Under light microscopy, the RLO was observed as intracytoplasmic inclusions within epithelial cells lining the post-esophagus and, to a minor extent, the intestine of H. diversicolor. Under transmission electron microscopy, inclusions were characterized as colonies of rod-shaped bacteria, 200 x 1800 nm in size, within a vesicle in the cytoplasm of the infected cell. The RLO from the small abalone bound with WS-RLO-specific in situ hybridization probes and was amplified by polymerase chain reaction (PCR), using primers designed from the 16S rDNA sequence of the original WS-RLO from California, USA. The PCR product of RLO samples from both the PRC and Thailand showed extremely high identity with the California WS-RLO (100 and 99%, respectively). These data combined with the history of abalone movements for aquaculture purposes indicate that RLOs observed in Thailand, Taiwan and the PRC are the WS-RLO that originated from California.

Pathogenic Vibrio harveyi, in contrast to non-pathogenic strains, intervenes with the p38 MAPK pathway to avoid an abalone haemocyte immune response

Vibrio harveyi is a marine bacterial pathogen responsible for episodic abalone epidemics associated with massive mortalities in France, Japan, and Australia. The aim of this study was the understanding of a possible role of the p38 MAPK in abalone haemocyte responses towards this bacterium. First, the pathogenicity of different V. harveyi strains was compared in both immersion and injection trials, and clear differences were detected. The three strains, ORM4, 04/092, and 05/053, all isolated from moribund abalone, induced up to 80% mortalities in immersion or injection challenges (LD(50) (ORM4) = 2.5 x 10(2) CFU animal(-1)). The two strains, LMG 4044T and LMG 7890 were non-pathogenic towards abalone in immersion trials, and needed very high numbers for killing by intramuscular injections (LD(50) = 8.9 x 10(4) and 1.6 x 10(5) CFU animal(-1), respectively). To start unraveling the mechanism explaining these differences, the p38-MAPK, a keyplayer in antimicrobial immune response, was studied. The non-pathogenic strain, LMG 7890 can be eliminated by abalone haemocytes and induces haemocyte phagocytosis and high ROS production. With different concentrations of a p38-specific inhibitor, SB203580, p38 implication was shown. This inhibitor reduced phagocytosis and ROS induction leading to LMG 7890 proliferation. In the case of the pathogenic ORM4 which can not be eliminated by abalone haemocytes, no phagocytosis and ROS production was induced, and a retarded p38 activation was observed. Taken together, our results suggest that p38 MAPK modulation may be one of the ways of virulent V. harveyi to attack its host and escape abalone immune response.

Detection of ostreid herpesvirus 1 DNA by PCR in bivalve molluscs: A critical review

Herpes-like viral infections have been reported in different bivalve mollusc species throughout the world. High mortalities among hatchery-reared larvae and juveniles of different bivalve species have been associated often with such infections. The diagnosis of herpes-like viruses in bivalve molluscs has been performed traditionally by light and transmission electron microscopy. The genome sequencing of one of these viruses, oyster herpesvirus 1 (OsHV-1), allowed the development of DNA-based diagnostic techniques. The polymerase chain reaction (PCR) has been used for the detection of OsHV-1 DNA in bivalve molluscs at different development stages. In addition, the PCR used for detection of OsHV-1 has also allowed the amplification of DNA from an OsHV-1 variant. The literature on DNA extraction methods, primers, PCR strategies, and confirmatory procedures used for the detection and identification of herpesviruses that infect bivalve molluscs are reviewed.

Mortality and herpesvirus infections of the Pacific oyster Crassostrea gigas in Tomales Bay, California, USA

Seed losses of Pacific oysters Crassostrea gigas have been associated with an ostreid herpesvirus-1 (OsHV-1) in Europe, and in 2002, a similar OsHV was detected in Tomales Bay, California, USA. In May of 2003, 5 stocks of seed Pacific oysters were planted at 2 sites (Inner Bay and Outer Bay) in Tomales Bay and monitored for mortality, presence/prevalence of OsHV (using polymerase chain reaction [PCR] and histology), and growth. Temperature (degrees C) and salinity data were collected every half an hour at each site. OsHV was detected at both the Inner and Outer Bay sites on the same sample date and mean temperature predicted OsHV presence (p < 0.005). High levels of mortality occurred 2 wk (Inner Bay site) and 4 wk (Outer Bay site) after OsHV detection. OsHV presence predicted mortality (p = 0.01). Temperature maximums and overall temperature exposure were greater at the Inner Bay site and may explain why mortality affected these oysters sooner than oysters planted at the Outer Bay site. Differences in cumulative mortality were significant among stocks (p < 0.0001), but not between sites (p > 0.05). OsHV prevalence was similar among stocks (p > 0.05) and between sites (p > 0.05). No evidence of herpesvirus-induced Cowdry type A nuclear inclusions or other pathogens were observed. Changes in tissue and cellular architecture including dilation of the digestive tubules and nuclear chromatin margination and pycnosis were observed in OsHV-infected oysters, consistent with previously observed OsHV infections. Stocks with smaller oysters had higher mortality rates than those with larger oysters; growth rate did not correlate with mortalities (p > 0.05). Taken together, these data suggest that the OsHV may cause or act in synergy with temperature to kill Pacific oyster seed in Tomales Bay, but further investigation of OsHV etiology in seed oysters is needed.

Health and survival of red abalone, Haliotis rufescens, under varying temperature, food supply, and exposure to the agent of withering syndrome

Withering syndrome (WS) is a disease of wild and cultured abalone caused by a Rickettsiales-like prokaryote (WS-RLP). This study compared the pathologic changes that occur during the progression of WS in red abalone to those caused by environmental stresses consisting of elevated temperature and food limitation and determined the impact of these stressors on WS prevalence and intensity. Farmed red abalone were administered a feed-based oxytetracycline therapeutic treatment to assure WS-RLP-free status prior to initiation of the experiment. Groups were then held in each of eight combinations of exposed vs. unexposed to WS-RLP, elevated vs. ambient temperature, and high vs. low food supply, for 447 days. Mortality was associated with starvation and disease but not elevated temperature alone. Elevated temperature significantly affected WS-RLP transmission: only 1.7% of WS-RLP- exposed abalone held at ambient temperature (12.3 degrees C) became infected compared to at least 72% of those held at elevated temperature (18.7 degrees C). Among exposed abalone at elevated temperature, fed animals exhibited greater infection prevalence but not greater infection intensity or digestive gland changes than starved animals, suggesting that abalone acquire infections by ingesting contaminated food. Food, temperature, WS-RLP exposure, and most of their interactions had significant effects on body condition and foot atrophy. Immunohistochemical detection of cell proliferation and apoptosis revealed no differences between normal digestive gland and that infected with WS-RLP. Body mass shrinkage, foot atrophy, elevated mortality, and decreased foot and digestive gland glycogen were observed in both WS-affected and starved, unexposed abalone, with the WS-RLP-exposed, starved group held at elevated temperature faring worst. Among exposed and unexposed animals, food supply but not temperature affected body mass and growth. These data demonstrate that the high morbidity and mortality exhibited by WS-RLP-infected abalone is a consequence of disease and not direct thermal stress. Drug residue analysis indicated oxytetracycline concentrations of up to 600 ppm in the digestive gland at 38 days post-treatment, an unusual degree of tissue retention of this therapeutant.

Pilot study of the Olympia oyster Ostrea conchaphila in the San Francisco Bay estuary: description and distribution of diseases

Olympia oysters Ostrea conchaphila have declined markedly during the last century and are a focus of restoration in many embayments, including the San Francisco Bay (SFB) estuary. Oysters were collected from 17 sites in this estuary and nearby Tomales Bay in an effort to characterize diseases that may impact recovery of this species and captive rearing programs. Three diseases/disease agents including a Mikrocytos-like protist (microcell), a haplosporidian and hemic neoplasia were observed from several sites along the western margins of the SFB estuary suggesting a geographic localization of disease presence. Based on fluoresecent in situ hybridization (FISH) assays, the microcell is distinct from M. mackini and Bonamia spp. These data highlight the need for further elucidation of the haplosporidian and for careful health management of a declining species destined for captive rearing and supplementation.

Herpes virus in juvenile Pacific oysters Crassostrea gigas from Tomales Bay, California, coincides with summer mortality episodes

Pacific Crassostrea gigas and eastern C. virginica oysters were examined between June 2002 and April 2003 from 8 locations along the east, west and south USA coasts for oyster herpes virus (OsHV) infections using the A primer set in a previously developed PCR test. Only surviving Pacific oysters from a mortality event in Tomales Bay, California, USA, where annual losses of oysters have occurred each summer since 1993, were infected with a herpes-like virus in 2002. PCR examination using template amounts of both 50 and 500 ng were essential for OsHV detection. Sequence analysis indicated that the Tomales Bay OsHV was similar to that identified in France with the exception of a single base pair substitution in a 917 bp fragment of the viral genome. However, unlike the French OsHV-1, the Tomales Bay OsHV did not amplify with the primer pair of a second OsHV-1 PCR assay, suggesting that further characterization of these viruses is warranted. No evidence of Cowdry type A viral infections characteristic of herpes virus infections or other pathogens were observed in OsHV-infected oysters. Hemocytosis, diapedesis and hemocyte degeneration characterized by nuclear pycnosis and fragmentation were observed in infected oysters, which is consistent with previous observations of OsHV infections in France. Together these data suggest that OsHV may be associated with the annual summer Pacific oyster seed mortality observed in Tomales Bay, but establishment of a causal relationship warrants further investigation.

Evaluation of mussel immune responses as indicators of contamination in San Francisco Bay

Several immune parameters were evaluated in two species of mussels (Mytilus californianus and M. galloprovincialis/M. trossulus) as bioindicators of contaminant effects. The mussels were deployed in San Francisco Bay Estuary and a control site at Bodega Marine Laboratory. Assays for phagocytosis and phagocytic index (average number of particles engulfed per hemocyte) were conducted with hemocytes in their own hemolymph-the "Serum" method. The responses were compared with contaminant concentrations in those mussels. For both species, the contaminated South Bay Dumbarton Bridge and Redwood Creek sites had elevated phagocytosis relative to the Bodega control site, indicating contaminant stress. The results also showed that M. californianus had higher percentages of phagocytosis (74%) and a higher phagocytic index (4.6 particles per cell) than those of M. galloprovincialis/M. trossulus (60% phagocytosis and 3.5 particles per cell). As there is a difference in immune response to contaminants, it is suggested that future San Francisco Estuary monitoring should be conducted with endemic M. galloprovincialis/M. trossulus rather than with the currently utilized M. californianus, which is not found in the estuary.

Pathogenicity testing of shellfish hatchery bacterial isolates on Pacific oyster Crassostrea gigas larvae

Bacterial diseases are a major cause of larval mortality in shellfish hatcheries. Even with proper sanitation measures, bacterial pathogens cannot be eliminated in all cases. The pathogenicity of bacteria isolated from Pacific Northwest shellfish hatcheries to Pacific oyster Crassostrea gigas larvae was investigated. We found 3 highly pathogenic strains and 1 mildly pathogenic strain among 33 isolates tested. These strains appear to be members of the genus Vibrio. Although there have been many studies of bivalve bacterial pathogens, a standard method to assess bacterial pathogenicity in bivalve larvae is needed. Thus, we developed 2 methods using either 15 ml conical tubes or tissue culture plates that were employed for rapidly screening bacterial strains for pathogenicity to Pacific oyster larvae. The tissue culture plates worked well for screening both mildly pathogenic strains and LD50 (lethal dose) assays. This method allowed for non-intrusive and non-destructive observation of the oyster larvae with a dissecting microscope. The LD50 for the 3 highly pathogenic strains ranged between 1.6 and 3.6 x 10(4) colony forming units (CFU) ml(-1) after 24 h and between 3.2 x 102 and 1.9 x 10(3) CFU ml(-1) after 48 h.

Pathology of cultured paua Haliotis iris infected with a novel haplosporidian parasite, with some observations on the course of disease

Mortalities among juvenile paua Haliotis iris Martyn 1784 in a commercial culture facility were reported in April 2000. Histology of moribund paua showed heavy systemic infections of a uni- to multi-nucleate stage of a novel organism later confirmed by transmission electron microscopy (TEM) and molecular studies to be a haplosporidian. Multinucleate plasmodia up to 25 microm diameter with up to 17 nuclei were detectable in wet preparations of hemolymph from heavily infected paua. The presence of the haplosporidian in the affected facility was associated with mortalities of slow growing 'runt' paua during the summer months. Total mortalities in affected raceways 6 mo after mortalities began were between 82.5 and 90%. Heavily infected paua exhibited behavioural abnormalities including lethargy, loss of righting reflex, and were easily detached from surfaces. Some heavily infected paua exhibited oedema and pale lesions in the foot and mantle, but no reliable gross signs of disease were noted. Light infections of the haplosporidian were also found in apparently healthy paua from the facility. Histology indicated that the early stages of infection were characterised by small numbers of plasmodia in the connective tissue surrounding the gut, amongst glial cells adjacent to nerves in the mantle and foot and within gill lamellae. In heavy infections, large numbers of small plasmodia (mean size 5.5 x 7 microm in histological sections) were present in the hemolymph, gills, heart, kidneys, mantle, foot, epipodium and connective tissue of the digestive gland. Infections were not transferred horizontally at 14 and 19 degrees C after cohabiting heavily infected paua with uninfected paua for 3 mo in aquaria, or 3 mo after injecting healthy paua with hemolymph containing haplosporidian plasmodia. This may indicate that the prepatent period for disease is longer than 3 mo, that disease is not expressed below 20 degrees C, or that an intermediate host is required for transmission. Spore formation was not observed in juvenile paua but sporocyst-like bodies containing putative spores were observed amongst haplosporidian plasmodia in the right kidney of poorly performing adult paua collected from the wild.

Detection of 'Candidatus Xenohaliotis californiensis' (Rickettsiales-like prokaryote) inclusions in tissue squashes of abalone (Haliotis spp.) gastrointestinal epithelium using a nucleic acid fluorochrome

Rickettsiales-like prokaryotes appear to be etiologic agents of a number of newly described diseases of fish and shellfish. 'Candidatus Xenohaliotis californiensis' is a Rickettsiales-like prokaryote responsible for withering syndrome, a fatal disease of wild and farmed Eastern Pacific abalone, Haliotis spp. The bacterium proliferates in gastrointestinal epithelial cells, forming large intracytoplasmic inclusions. We describe a method of rapidly detecting and assessing the intensity of 'Candidatus Xenohaliotis californiensis' infections in abalone gastrointestinal tissue using the nucleic acid-specific fluorochrome Hoechst 33258. In excised tissue pieces dried onto slides, rehydrated in the Hoechst stain and viewed with ultraviolet light, the large bacterial inclusions were strongly fluorescent and could be easily distinguished from smaller host cell nuclei. This provided a rapid, inexpensive alternative to paraffin section microscopy or molecular techniques, allowing detection of the pathogen within minutes of tissue excision. Comparison of the fluorochrome method with conventional histological analysis for the ability to detect inclusions in 109 samples was 90% accurate, with discrepancies due to false negative diagnosis of low-level infections. An alternative nucleic acid-specific fluorochrome, propidium iodide, showed a staining pattern identical to that of Hoechst 33258. These methods should prove useful for the rapid detection of inclusion-forming Rickettsiales-like prokaryotes in tissues from many host species.

Combined effects of pentachlorophenol and salinity stress on phagocytic and chemotactic function in two species of abalone

The effect of pentachlorophenol (PCP) combined with salinity stress on specific aspects of cellular immunity was examined in two species of abalone. Chemotactic and phagocytic ability (percent phagocytosis, %P; and phagocytic index, PI), as well as gross morphological characteristics, of hemocytes withdrawn from red (Haliotis rufescens) and black abalone (H. cracherodii) after in vivo exposure to 25, 35, or 45 per thousand seawater salinity plus 1.2 mg/l PCP were determined. Abalone exposures of 3.5 and 6.5 h, respectively, were based on species-specific metabolic endpoints (MEPs) derived from previous NMR data. Hemocyte chemotaxis was found to be augmented by low salinity in red but not black abalone, while high salinity seemed to reduce chemotactic ability in both species. PCP did not potentiate the effects demonstrated by salinity variations alone in red abalone, although chemotaxis was further compromised in black abalone exposed to high salinity stress combined with PCP. Although chemotactic ability was similar among both species, both %P and PI was greater among black abalone. Low salinity may offset the effects of PCP in red but not black abalone. Whereas red abalone demonstrated a reduction in phagocytic ability upon exposure to high salinity alone, black abalone appeared more resilient to high salinity stress alone. Furthermore, while the effect of high salinity plus PCP is subadditive among red abalone, high salinity seems to potentiate the effect of PCP on black abalone. Finally, hemocytes exposed to acute salinity variations plus PCP showed varying morphological characteristics when compared to controls. Over 30% of hemocytes of high salinity plus PCP exposed abalone remained rounded and generally unattached to glass slides with only a few pseudopod extensions. Hemocyte preparations incubated in rhodamine-conjugated phalloidin were observed with fluorescence microscopy and reveal an altered actin filament pattern. Overall, black abalone demonstrate greater phagocytic ability than red abalone both in the presence and absence of PCP. Furthermore, increases in salinity are accompanied with reduced phagocytic ability with red abalone demonstrating particular sensitivity to salinity variations. While PCP inhibits ATP synthesis, salinity variations may impose an additional stress on intertidal animals exposed to transient or seasonal environmental changes.

Withering Syndrome in Farmed Red Abalone Haliotis rufescens: Thermal Induction and Association with a Gastrointestinal Rickettsiales-like Prokaryote

Withering syndrome (WS) is a chronic wasting disease responsible for mass mortality in wild populations of black abalone Haliotis cracherodii. The etiology of WS is uncertain with limited evidence for the role of a gastrointestinal Rickettsiales-like prokaryote (RLP). We documented for the first time the occurrence of animals with clinical signs of WS and associated morphological changes in another haliotid species, the red abalone H. rufescens. In this study, 60 juvenile red abalone (8 cm) were randomly selected from a farmed population raised at 14°C that was known to have low-intensity RLP infections but lacked clinical signs of WS. The abalone were held in triplicate containers receiving water of approximately 14.7°C (Control, Co) or 18.5°C (elevated temperature, ET) and were fed equally for 220 d. Survival was 100% (30/30) for the Co group and 67% (20/30) for the ET group. The ET group animals had higher RLP infection intensities and showed more clinical signs (mantle retraction, lower weight gain, lower condition index) and morphological changes (digestive gland degeneration) associated with WS. In trials conducted immediately before termination of the experiment, ET group animals fed at half the rate of Co group animals. Among ET group animals, the intensity of RLP infections in the posterior portion of the esophagus was positively correlated with WS clinical signs and morphological changes, whereas no correlations were present among Co group animals. During 1997-1998 and in conjunction with elevated seawater temperatures associated with El Niño, several abalone farms in California experienced a dramatic increase in the proportion of red abalone showing signs of WS. Examination of 66 red abalone from five commercial farms revealed that animals with more advanced RLP infections had more severe WS clinical signs and associated morphological changes. Collectively, these data demonstrate that RLP infection plays a key role in the etiology of WS in red abalone and that warm water enhances the severity of the pathogenic effects of RLP infection.

'Candidatus Xenohaliotis californiensis', a newly described pathogen of abalone, Haliotis spp., along the west coast of North America

Withering syndrome is a fatal disease of wild and cultured abalone, Haliotis spp., that inhabit the west coast of North America. The aetiological agent of withering syndrome has recently been identified as a member of the family Rickettsiaceae in the order Rickettsiales. Using a combination of morphological, serological, life history and genomic (16S rDNA) characterization, we have identified this bacterium as a unique taxon and propose the provisional status of 'Candidatus Xenohaliotis californiensis'. The Gram-negative, obligate intracellular pleomorphic bacterium is found within membrane-bound vacuoles in the cytoplasm of abalone gastrointestinal epithelial cells. The bacterium is not cultivable on synthetic media or in fish cell lines (e.g. CHSE-214) and may be controlled by tetracyclines (oxytetracycline) but not by chloramphenicol, clarithromycin or sarafloxicin. Phylogenetic analysis based on the 16S rDNA of 'Candidatus Xenohaliotis californiensis' places it in the alpha-subclass of the class Proteobacteria but not to the four recognized subtaxa of the alpha-Proteobacteria (alpha-1, alpha-2, alpha-3 and alpha-4). The bacterium can be detected in tissue squashes stained with propidium iodide, microscopic examination of stained tissue sections, PCR or in situ hybridization. 'Candidatus Xenohaliotis californiensis' can be differentiated from other closely related alpha-Proteobacteria by its unique 16S rDNA sequence.