Spatial distribution of mortality in Pacific oysters Crassostrea gigas: reflection on mechanisms of OsHV-1 transmission

The ostreid herpesvirus (OsHV-1) has the potential to devastate Crassostrea gigas culture in Australia as it has done in many other countries, highlighting the need for a better understanding of disease expression and transmission. The aim of this study was to assess the spatial distribution of OsHV-1 associated mortalities in one of only two infected areas in Australia, Woolooware Bay (Botany Bay New South Wales). In October 2011, healthy sentinel Pacific oysters were placed in three different locations at three different tidal levels and OsHV-1 associated mortalities were closely monitored over 7 months. The outbreak started in November 2011 and the disease remained active until April 2012. Three major mortality events were detected. Rather than being a propagating epizootic, it appeared that most oysters were infected from the same environmental source. The distribution of OsHV-1 associated mortalities was spatially clustered, highly variable and clearly dependent on the age of oysters and their position in the water column. Non-random distribution of mortalities at macro scale (sites several km apart) and micro scale (within rearing trays), and vertical clustering patterns in the water column are discussed in relation to mechanisms of transmission in water. We hypothesise that OsHV-1 may be carried through water by particles, possibly plankton. Key words: Crassostrea gigas, Ostreid herpesvirus 1, summer mortalities, spatial distribution, plankton, disease transmissionFunded by the Fisheries Research and Development Corporation, the University of Sydney and the Sydney Metropolitan Catchment Management Authorit

Experimental infections of Pacific oyster Crassostrea gigas using the Australian OsHV-1 µVar strain

In Australia the spread of the Ostreid herpesvirus OsHV-1 microvariant (OsHV-1 µVar) threatens the Pacific oyster industry. There was an urgent need to develop an experimental infection model in order to study the pathogenesis of the virus in controlled laboratory conditions. The present study constitutes the first attempt to use archived frozen oysters as a source of inoculum, based on the Australian OsHV-1 µVar strain. Experiments were conducted to test (i) the virus infectivity, (ii) the dose-response relationship for OsHV-1, and (iii) the best storage conditions to keep infective viral inoculum. Intramuscular injection of a viral inoculum consistently led to an onset of mortality 48h post injection and a final cumulative mortality exceeding 90%, in association with high viral loads (1 x 105 – 3 x 107 copies of virus mg-1) in dead individuals. For the first time an infective inoculum was produced from frozen oysters (tissues stored at -80°C for 6 months). Storage of purified viral inoculum at +4°C for 3 months provided similar results to use of fresh inoculum whereas storage at -20°C, -80°C and room temperature was detrimental to infectivity. A dose-response relationship for OsHV-1 was identified but further research is recommended to determine the most appropriate viral concentration for development of infection models that would be used for different purposes. Overall, this work highlights the best practices and potential issues that may occur in the development of a reproducible and transferable infection model for studying the pathogenicity of the Australian OsHV-1 strain in C. gigas under experimental conditions. Keywords: Ostreid herpesvirus 1; Crassostrea gigas; experimental infection model; dose-response; inoculum preparation; storage condition

Descriptive epidemiology of mass mortality due to Ostreid herpesvirus-1 (OsHV-1) in commercially farmed Pacific oysters (Crassostrea gigas) in the Hawkesbury River estuary, Australia

postprintMortality of farmed triploid Pacific oysters (Crassostrea gigas) associated with Ostreid herpesvirus-1 (OsHV-1) was first recorded in Australia in the Georges River/Botany Bay estuary (New South Wales) in late 2010. Two years later, the first sign of possible inter-estuarine spread was observed when commercial triploid Pacific oysters in the Hawkesbury River estuary, located 50 km north of Botany Bay, were affected by mass mortality. The aim of this study was to describe the epidemiological features of the Hawkesbury outbreak via a formal investigation which was conducted in real time and comprised: an assessment of stock levels, past oyster acquisitions and a trace forward investigation to identify stock at greatest risk due to transfers of oysters; passive surveillance of the spread of mortalities in the estuary; active surveillance using PCR to identify the distribution of OsHV-1 infection on farms in the estuary and mortality estimates to identify age and size classes affected; identification of the time of first infection using data from sentinel oysters; and assessment of environmental risk factors. Mortalities were recorded in all age classes but were greater in spat and juveniles than in adults. The incubation period for mass mortality was < 4 days, however subclinical OsHV-1 infection was detected three months prior to the first signs of mortality in the index case (first location affected), which suggests that low viral loads of OsHV-1 are insufficient to induce the disease. While inefficient oyster-to-oyster transmission occurred at two locations, a synchronous infection arising from a common environmental source was required to explain the mass mortalities at the index case (Mullet Creek). Estuarine hydrodynamics then assisted rapid dispersal of viral particles throughout the estuary. Seawater temperatures were consistently above 24°C during the month preceding mass mortalities with variations (± 3°C) being observed over a few days during this period; however this did not necessarily lead to mortality events when the virus was present. There was no evidence of prior movement of potentially infected oysters or farming equipment into the Hawkesbury River estuary to explain the outbreak. Key words: Disease outbreak investigation; Pacific oysters; Ostreid herpesvirus-1; disease transmission; incubation period; water temperature; epidemiologyFunded by the Fisheries Research Development and Corporation (FRDC), The University of Sydney and the Sydney Metropolitan Catchment Management Authorit

The Shape and Scale of Galactic Rotation from Cepheid Kinematics

A catalog of Cepheid variables is used to probe the kinematics of the Galactic disk. Radial velocities are measured for eight distant Cepheids toward l = 300; these new Cepheids provide a particularly good constraint on the distance to the Galactic center, R_0. We model the disk with both an axisymmetric rotation curve and one with a weak elliptical component, and find evidence for an ellipticity of 0.043 +/- 0.016 near the Sun. Using these models, we derive R_0 = 7.66 +/- 0.32 kpc and v_circ = 237 +/- 12 km/s. The distance to the Galactic center agrees well with recent determinations from the distribution of RR Lyrae variables, and disfavors most models with large ellipticities at the solar orbit.Comment: 36 pages, LaTeX, 10 figure

Different Host Exploitation Strategies in Two Zebra Mussel-Trematode Systems: Adjustments of Host Life History Traits

The zebra mussel is the intermediate host for two digenean trematodes, Phyllodistomum folium and Bucephalus polymorphus, infecting gills and the gonad respectively. Many gray areas exist relating to the host physiological disturbances associated with these infections, and the strategies used by these parasites to exploit their host without killing it. The aim of this study was to examine the host exploitation strategies of these trematodes and the associated host physiological disturbances. We hypothesized that these two parasite species, by infecting two different organs (gills or gonads), do not induce the same physiological changes. Four cellular responses (lysosomal and peroxisomal defence systems, lipidic peroxidation and lipidic reserves) in the host digestive gland were studied by histochemistry and stereology, as well as the energetic reserves available in gonads. Moreover, two indices were calculated related to the reproductive status and the physiological condition of the organisms. Both parasites induced adjustments of zebra mussel life history traits. The host-exploitation strategy adopted by P. folium would occur during a short-term period due to gill deformation, and could be defined as “virulent.” Moreover, this parasite had significant host gender-dependent effects: infected males displayed a slowed-down metabolism and energetic reserves more allocated to growth, whereas females displayed better defences and would allocate more energy to reproduction and maintenance. In contrast, B. polymorphus would be a more “prudent” parasite, exploiting its host during a long-term period through the consumption of reserves allocated to reproduction

The spatial pattern of premature mortality in Hong Kong: how does it relate to public housing?

Research into understanding the relationship between access to housing, health and wellbeing in cities has yielded mixed evidence to date and has been limited to case studies from Western countries. Many studies appear to highlight the negative effects of public housing in influencing the health of its residents. Current trends in the urban housing markets in cities of advanced Asian economies and debates surrounding the role of government in providing housing underscore the need for more focused research into housing and health. In this paper, we investigate Hong Kong as an example of a thriving Asian city by exploring and comparing the intra-urban geographies of premature mortality and public housing provision in the city. Using a fully Bayesian spatial structural model, we estimate associations between public housing provision and different types of premature mortality. We find significant geographic variations in premature mortality within Hong Kong during the five-year period 2005–2009, with positive associations between the residents of public housing and premature mortality risk. But the associations attenuate or are even reversed for premature mortality of injuries and non-communicable diseases after controlling for local deprivation, housing instability, access to local amenities and other neighbourhood characteristics. The results indicate that public housing may have a protective effect on community health, which contradicts the findings of similar studies carried out in Western cities. We suggest reasons why the association between public housing and health differs in Hong Kong and discuss the implications for housing policy in Hong Kong and other Asian cities

Genome-wide fitness analyses of the foodborne pathogen Campylobacter jejuni in in vitro and in vivo models.

Campylobacter is the most common cause of foodborne bacterial illness worldwide. Faecal contamination of meat, especially chicken, during processing represents a key route of transmission to humans. There is a lack of insight into the mechanisms driving C. jejuni growth and survival within hosts and the environment. Here, we report a detailed analysis of C. jejuni fitness across models reflecting stages in its life cycle. Transposon (Tn) gene-inactivation libraries were generated in three C. jejuni strains and the impact on fitness during chicken colonisation, survival in houseflies and under nutrient-rich and -poor conditions at 4 °C and infection of human gut epithelial cells was assessed by Tn-insertion site sequencing (Tn-seq). A total of 331 homologous gene clusters were essential for fitness during in vitro growth in three C. jejuni strains, revealing that a large part of its genome is dedicated to growth. We report novel C. jejuni factors essential throughout its life cycle. Importantly, we identified genes that fulfil important roles across multiple conditions. Our comprehensive screens showed which flagella elements are essential for growth and which are vital to the interaction with host organisms. Future efforts should focus on how to exploit this knowledge to effectively control infections caused by C. jejuni.This work was funded by Biotechnology and Biological Sciences Research Council (http://www.bbsrc.ac.uk) grant BB/K004514/1. D.P.W. was funded by a Wellcome Trust (https://wellcome.ac.uk) Infection and Immunity PhD rotation studentship. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript