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Peer Reviewed

Examining the Roles of Environment, Host, and Pathogen in the Host-Pathogen Relationship Between the Oyster Herpesvirus and the Pacific Oyster

Burge, Colleen A.

Research Theses and Dissertations (2010)

The Pacific oyster, Crassostrea gigas, an oyster species indigenous to Japan, has been introduced globally becoming the primary species of oyster cultured in many areas of the world. In Tomales Bay, California, seed mortalities have occurred in Pacific oysters nearly annually since 1993, and the oyster herpesvirus (OsHV), a virulent pathogen of larval and juvenile bivalves (particularly known in Pacific oysters) was first detected in 2002. Sentinel field studies (2000-2003) were conducted in Tomales Bay in order to better understand the role of environmental factors (temperature, phytoplankton, and salinity) and oyster health (measured using histology and/or OsHV-specific Polymerase Chain Reaction (PCR)) on Pacific oyster survival. Elevated temperatures were the only environmental factor consistently related to mortalities (2000-2003), and in 2003, elevated temperature means predicted OsHV presence (p < 0.005); OsHV presence predicted mortality (p=0.01). A separate survey conducted in 2003 detected OsHV in multiple species of bivalves grown in Tomales Bay (C. gigas, Ostrea edulis, C. virginica, C. sikamea, Mytilus galloprovincialis, and Venerupis phillipinarum) and C. gigas grown in nearby Drakes Bay using OsHV-specific PCR and/or quantitative PCR (qPCR); qPCR copy numbers were low in each species tested but were significantly greater in C. gigas (p < 0.0001) the only species that appear to be impacted by mortalities. To confirm the infectious etiology of OsHV detected in Tomales Bay, Pacific oyster larvae were exposed to either filtered homogenates from OsHV-infected Pacific oysters in Tomales Bay or uninfected oyster tissue. OsHV was detected and quantified only in oyster larvae exposed to OsHV using qPCR and reverse transcriptase qPCR, and confirmed using transmission electron microscopy. Taken together, data from field and lab-based experiments indicates an infectious disease (OsHV) acts in synergy with temperature to kill Pacific oysters in Tomales Bay, California. Preliminary gene identification of both upregulated host and OsHV genes in larvae exposed to OsHV was conducted using SOLiD sequencing and GeneFishing PCR. Genes identified may provide a foundation to better understand both host response and virus infection, ultimately better defining the hostpathogen relationship between OsHV and Pacific oysters.

Cover page: Examining the Roles of Environment, Host, and Pathogen in the Host-Pathogen Relationship Between the Oyster Herpesvirus and the Pacific Oyster

Article
Peer Reviewed

Metagenome-assembled genome of withering syndrome causative agent, Candidatus Xenohaliotis californiensis, from endangered white abalone (Haliotis sorenseni).

UC San Diego Previously Published Works (2024)

The genome of Candidatus Xenohaliotis californiensis was assembled from shotgun metagenomic sequencing of experimentally infected white abalone. Ninety-one percent genome completeness was achieved with low contamination. Sequencing this genome provides the opportunity to track pathogen evolution over time, conduct gene expression experiments, and study dynamics between this pathogen and its phage.

Cover page: Metagenome-assembled genome of withering syndrome causative agent, Candidatus Xenohaliotis californiensis, from endangered white abalone (Haliotis sorenseni).

Article
Peer Reviewed

Densovirus associated with sea-star wasting disease and mass mortality

UC Santa Cruz Previously Published Works (2014)

Populations of at least 20 asteroid species on the Northeast Pacific Coast have recently experienced an extensive outbreak of sea-star (asteroid) wasting disease (SSWD). The disease leads to behavioral changes, lesions, loss of turgor, limb autotomy, and death characterized by rapid degradation ("melting"). Here, we present evidence from experimental challenge studies and field observations that link the mass mortalities to a densovirus (Parvoviridae). Virus-sized material (i.e., <0.2 μm) from symptomatic tissues that was inoculated into asymptomatic asteroids consistently resulted in SSWD signs whereas animals receiving heat-killed (i.e., control) virus-sized inoculum remained asymptomatic. Viral metagenomic investigations revealed the sea star-associated densovirus (SSaDV) as the most likely candidate virus associated with tissues from symptomatic asteroids. Quantification of SSaDV during transmission trials indicated that progression of SSWD paralleled increased SSaDV load. In field surveys, SSaDV loads were more abundant in symptomatic than in asymptomatic asteroids. SSaDV could be detected in plankton, sediments and in nonasteroid echinoderms, providing a possible mechanism for viral spread. SSaDV was detected in museum specimens of asteroids from 1942, suggesting that it has been present on the North American Pacific Coast for at least 72 y. SSaDV is therefore the most promising candidate disease agent responsible for asteroid mass mortality.