R J Whittington

University of Sydney, Sydney, New South Wales, Australia

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Publications (204)463.96 Total impact

  • [Show abstract] [Hide abstract]
    ABSTRACT: Abstract Mycobacteria have a complex cell wall with a high lipid content that confers unique advantages for bacterial survival in the hostile host environment, leading to long-term infection. There is a wealth of evidence suggesting the role cell wall-associated lipid antigens play at the host-pathogen interface by contributing to bacterial virulence. One pathway that pathogenic mycobacteria use to subvert host immune pathways to their advantage is host cholesterol/lipid homeostasis. This review focuses on the possible role of pathogen- and host-associated lipids in the survival and persistence of pathogenic mycobacteria with emphasis on Mycobacterium avium subsp. paratuberculosis. We draw upon literature in diverse areas of infectious and metabolic diseases and explain a mechanism by which mycobacterial-induced changes in the host cellular energy state could account for phenomena that are a hallmark of chronic mycobacterial diseases.
    Critical reviews in microbiology. 08/2014;
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    PA Windsor, J Eppleston, NK Dhand, RJ Whittington
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    ABSTRACT: Objective Examine the prevalence of shedding of Mycobacterium avium subsp. paratuberculosis (Mptb) at least 5 years after starting vaccination with Gudair™ in flocks of varying initial prevalence of ovine Johne's disease (OJD) and identify risk factors for variation in vaccine efficacy.Methods Pooled faecal culture (PFC) was conducted for 41 flocks from southern NSW and Victoria to determine estimates of current OJD prevalence. The data were compared to estimates of prevalence at or prior to commencement of vaccination at least 5 years earlier, based on available serological or PFC tests when vaccination commenced. A cross-sectional study was conducted to identify risk factors for differing prevalence levels in 36 of the flocks.ResultsHistorical data enabled classification of 37 flocks as high (13; 35.1%), medium (10; 27.0%) or low (14; 37.8%) estimated initial OJD prevalence. Results of PFC in 2008–09 identified that 81.1% (30/37) of flocks had detectable shedders, with 48.6% (18/37) flocks still classified as medium or high OJD prevalence, including 50% (7/14) of flocks initially classified as low prevalence. Shedding was not detected in 18.9% (7/37) flocks. Flocks with OJD prevalence exceeding 1% at 5 years or more following the commencement of vaccination were associated with reports of sheep straying and introduction of new sheep.Conclusion Despite significant declines in estimated OJD prevalence following vaccination for ≥5 years, 81.1% of flocks were shedding Mptb and considered at risk of spreading the disease or suffering recrudescence of losses if vaccination were to cease. Flock managers are advised to persist with vaccination.
    Australian Veterinary Journal 07/2014; 92(7). · 0.92 Impact Factor
  • Om Dhungyel, James Hunter, Richard Whittington
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    ABSTRACT: Research on footrot in small ruminants, which is caused by Dichelobacter nodosus, has led to development of vaccines and their application for control, treatment and eradication of the disease in sheep. Footrot vaccines have evolved over decades to contain monovalent whole cell, multivalent recombinant fimbrial, and finally mono or bivalent recombinant fimbrial antigens. Initially whole cell vaccines made against the few known serogroups of D. nodosus were found to be inefficient in control of the disease in the field, which was attributed to the presence of other unidentified serogroups and also the use of inefficient adjuvants. Fimbriae or pili, which are the basis for antigenic variation, were found to be the major protective and also curative antigens but they are not cross protective between the different serogroups. Multivalent vaccines incorporating all the known serogroups have been proven to be of limited efficacy due to the phenomenon of antigenic competition. Recent studies in Nepal, Bhutan and Australia have shown that outbreak-specific vaccination which involves targeting identified serogroups with mono- or bivalent recombinant fimbrial vaccines, can be very effective in sheep and goats. Where multiple serogroups are present in a flock, antigenic competition can be overcome by sequentially targeting the serogroups with different bivalent vaccines every 3 months. A common antigen which would confer immunity to all serogroups would be the ideal immunogen but the initial studies were not successful in this area. Until universal antigen/s are available, flock specific mono or bivalent fimbrial vaccines are likely to be the most effective tool for control and eradication of footrot in sheep and goats. Future research in footrot vaccines should be focused on improving the duration of prophylaxis by incorporating new and emerging immunomodulators or adjuvants with modified delivery vehicles, discovering a common antigen and understanding the mechanisms of acquired immunity.
    Vaccine 04/2014; · 3.77 Impact Factor
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    ABSTRACT: Johne's disease in ruminants is a chronic infection of the intestines caused by Mycobacterium avium subspecies paratuberculosis. An important strategy to control disease is the early detection and a potentially efficient method for early detection by measuring cell mediated immune responses developed by the host in response to exposure or infection. One method is to measure lymphoproliferation and cytokine release from the host cells when exposed to the organism or parts of the organism. In this study, ten recombinant MAP proteins known to be upregulated under in vitro stress conditions were evaluated by examining their ability to evoke memory as a result of exposure by vaccination or oral challenge with live Mycobacterium avium subspecies paratuberculosis. Out of ten proteins MAP2698c was found to induce higher cell mediated immune responses in vaccinated and challenged sheep in comparison to healthy controls. The findings suggest that not all stress regulated proteins have the diagnostic potential to detect cell mediated immune responses in ovine paratuberculosis.
    Clinical and vaccine Immunology: CVI 04/2014; · 2.60 Impact Factor
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    ABSTRACT: The duration of survival of both the S and C strains of Mycobacterium avium subsp. paratuberculosis in faeces were quantified in contrasting climatic zones of New South Wales and detailed environmental temperature data were collected. Known concentrations of S and C strains in faeces placed on soil in polystyrene boxes were exposed to the environment with or without the provision of shade (70%) at Bathurst, Armidale, Condobolin and Broken Hill and sub-samples taken every 2 weeks were cultured for the presence of M. avium subsp. paratuberculosis. The duration of survival ranged from a minimum of 1 week to a maximum of 16 weeks and the provision of 70% shade was the most important factor in extending survival time. The hazard of death for exposed compared to shaded samples was 20 and 9 times higher for S and C strains, respectively. Site did not affect survival of C strain but for the S strain, the hazard of death was 2.3 times higher at the two arid zone sites (Broken Hill and Condobolin) than at the two temperate sites (Bathurst and Armidale). Temperature measurements revealed maximum temperatures exceeding 60°C and large daily temperature ranges at the soil surface, particularly in exposed boxes.
    Applied and environmental microbiology 01/2014; · 3.69 Impact Factor
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    ABSTRACT: Mortality 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 site (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 site (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.
    Aquaculture. 01/2014; s 422–423:146–159.
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    ABSTRACT: Evasion of host defense mechanisms and survival inside infected host macrophages are features of pathogenic mycobacteria including Mycobacterium avium subspecies paratuberculosis, the causative agent of Johne's disease in ruminants. Protein tyrosine phosphatase A (PtpA) has been identified as a secreted protein critical for survival of mycobacteria within infected macrophages. The host may mount an immune response to such secreted proteins. In this study, the humoral immune response to purified recombinant Mycobacterium avium subsp. paratuberculosis PtpA was investigated using sera from a cohort of sheep infected with Mycobacterium avium subsp. paratuberculosis and compared with uninfected healthy controls. A significantly higher level of reactivity to PtpA was observed in sera collected from Mycobacterium avium subspecies paratuberculosis infected sheep when compared to those from uninfected healthy controls. PtpA could be a potential candidate antigen for detection of humoral immune responses in sheep infected with Mycobacterium avium subspecies paratuberculosis.
    Veterinary Immunology and Immunopathology 01/2014; · 1.88 Impact Factor
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    Ratna B Gurung, Auriol C Purdie, Richard J Whittington, Douglas J Begg
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    ABSTRACT: Control of Johne's disease, caused by Mycobacterium avium subspecies paratuberculosis (MAP) in ruminants using commercially available vaccine reduces production losses, mortality, fecal shedding and histopathological lesions but does not provide complete protection from infection and interferes with serological diagnosis of Johne's disease and bovine tuberculosis. At this time no recombinant antigens have been found to provide superior protection compared to whole killed or live-attenuated MAP vaccines. Therefore, there is a need to evaluate more candidate MAP antigens. In this study recombinant MAP antigens MAP2698c and MAP3567 were formulated with four different MONTANIDE™ (ISA 50V2, 61VG, 71VG, and 201VG) adjuvants and evaluated for their ability to produce specific immune responses in vaccinated sheep. The cellular immune response was measured with an interferon-gamma (IFN-γ) release assay and the humoral immune response was measured by antibody detection enzyme linked immunosorbent assay. Recombinant vaccine formulation with the antigen MAP2698c and MONTANIDE™ ISA 201VG adjuvant produced strong whole-MAP as well as MAP2698c-specific IFN-γ responses in a high proportion of the vaccinated sheep. The formulation caused less severe injection site lesions in comparison to other formulations. The findings from this study suggest that the MAP2698c + 201VG should be evaluated in a challenge trial to determine the efficacy of this vaccine candidate.
    Frontiers in Cellular and Infection Microbiology 01/2014; 4:93.
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    ABSTRACT: The international trade in ornamental fish is considered a major factor for the transboundary spread of aquatic pathogens that can affect both wild and farmed fish populations. Nearly 18 million ornamental fish were imported into Australia in 2007, including approximately 3.9 million goldfish. Despite quarantine regulations during importation, there have been several incidents in Australia where exotic pathogens from ornamental fish have become established in farmed or free-living fish species. The exotic virus Cyprinid herpesvirus 2 (CyHV2) was first found in Australia in 2003 in goldfish, suggesting that sub-clinically infected goldfish were passing through quarantine regardless of health certification and three weeks of quarantine. Repeated cross sectional surveys were conducted to determine whether CyHV2 has already established in farmed or wild ornamental fish in Australia. Goldfish populations were tested to OIE standard to detect 2% prevalence with 95% confidence assuming a test of 100% sensitivity and specificity. CyHV2 was found at retail outlets, farms and in several populations of wild goldfish in the ACT and Victoria. The prevalence and moderate to high viral loads in sub-clinically infected goldfish from different domestic populations suggested the introduction was not a recent event. This study demonstrated that CyHV2 has established in Australia and informed quarantine policy to revoke the requirement for goldfish exported to Australia to be certified free of CyHV2. The results provided clear evidence that an aquatic pathogen from imported ornamental fish can become established in farmed and wild populations. This is of particular significance to Australia as there are many endemic and ecologically sensitive populations of fish that may be severely affected by exotic pathogens. The incursion of CyHV2 in Australia should be considered a case study to inform pathway analysis for pathogen establishment.
    Aquaculture. 01/2014; 432:53–59.
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    ABSTRACT: Johne's disease (JD) is a chronic disease affecting ruminants and other species caused by the pathogenic mycobacterium, Mycobacterium avium subsp. paratuberculosis (MAP). MAP has developed a multitude of mechanisms to persist within the host, and these in turn are counteracted by the host through various immune pathways. Identifying and characterising the different strategies employed by MAP to alter the host immune system in its favour, and thereby persist intracellularly, could hold the key to developing strategies to fight this disease. In this study we analysed a subset of bovine microarray data derived from early time points after experimental infection with MAP. A specifically developed integrated approach was used to identify and validate host genes involved in cholesterol homeostasis (24DHCR, LDLR, SCD-1), calcium homeostasis and anti-bacterial defence mechanisms, (CD38, GIMAP6) which were downregulated in response to MAP exposure. A trend for upregulation of granulysin gene expression in MAP-exposed cattle in comparison to unexposed cattle was also observed. From these analyses, a model of potential pathogen-host interactions involving these novel pathways was developed which indicates an important role for host lipids in mycobacterial survival and persistence.
    Veterinary Immunology and Immunopathology 01/2014; · 1.88 Impact Factor
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    ABSTRACT: Johne's disease (JD) is a chronic enteric disease caused by Mycobacterium avium subsp. paratuberculosis that affects ruminants. Transmission is by the faecal-oral route. A commonly used ante-mortem diagnostic test for the detection of M. avium subsp. paratuberculosis in faeces is liquid culture, however a major constraint is the 2-3 months incubation period. Rapid detection methods for M. avium subsp. paratuberculosis based on PCR have been reported but comprehensive validation data are lacking. We describe a new test, High-Throughput-Johnes (HT-J), to detect M. avium subsp. paratuberculosis in faeces. Diagnostic accuracy was compared with liquid radiometric (BACTEC) faecal culture using samples from cattle (n=1330; 23 herds) and sheep (n=596; 16 flocks). The multistage protocol involves recovery of M. avium subsp. paratuberculosis cells from a faecal suspension, cell rupture by bead beating, extraction of DNA using magnetic beads and IS900 quantitative PCR. The limit of detection of the assay was 0.0005 pg and limit of quantification was 0.005 pg M. avium subsp. paratuberculosis genomic DNA. Only M. avium subsp. paratuberculosis was detected from a panel of 51 mycobacterial isolates, including 10 with IS900-like sequences. Of the 549 culture negative faecal samples from unexposed herds and flocks, 99% were negative in the HT-J test while 60% of bovine and 84% of ovine culture positive samples were positive in the HT-J test. As similar total numbers of samples from M. avium subsp. paratuberculosis-exposed animals were positive in culture and HT-J tests in both species, and as a McNemar's test was not significant, these methods probably have similar sensitivity, but the true diagnostic sensitivity of either test is unknown. These validation data meet consensus-based reporting standards for diagnostic test accuracy studies for paratuberculosis and Minimum Information for Publication of Quantitative Real-Time PCR Experiments (MIQE) guidelines. The HT-J assay has been approved for use in JD control programs in Australia and New Zealand.
    Journal of clinical microbiology 12/2013; · 4.16 Impact Factor
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    ABSTRACT: Mycobacterium avium subsp paratuberculosis (MAP) causes Johne's disease (JD) in ruminants. Proteomic studies have shown that MAP expresses certain proteins when exposed to in vitro physiological stress conditions similar to the conditions experienced within a host during natural infection. Such proteins were hypothesised to be expressed in vivo, are recognised by the host immune system and may be of potential use in diagnosis of JD. In this study, 50 recombinant maltose binding protein (MBP) fusion MAP proteins were evaluated using serum samples from sheep infected with MAP and 29 (58%) were found to be antigenic. Among 50 fusion proteins 10 were evaluated in MBP fusion and Factor Xa cleaved forms. A total of 31 (62%) proteins were found to be antigenic either in MBP fused or Factor Xa cleaved forms. Antigenicity after cleaving and removal of the MBP tag was marginally enhanced.
    Clinical and vaccine Immunology: CVI 10/2013; · 2.60 Impact Factor
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    ABSTRACT: Liquid culture of Mycobacterium avium subsp. paratuberculosis (MAP) from clinical samples such as feces is the most sensitive ante-mortem test for diagnosis of Johne's disease in ruminants. In Australia, New Zealand, the USA and some other countries the BACTEC 460 system with modified BACTEC 12B medium (Becton Dickinson) has been the most commonly used liquid culture system, but it was discontinued in 2012. In this study a new liquid culture medium M7H9C was developed. It consists of Middlebrook 7H9 medium base with added casitone, albumin, dextrose, catalase, egg yolk, mycobactin J and a cocktail of antibiotics. Polyoxyethylene stearate (POES) was not essential for cultivation of MAP in either BACTEC 12B or M7H9C medium. The limit of detection determined using pure cultures of both C and S strains of MAP was 7 bacilli per 50 μl inoculum in both media. The new medium was validated using 784 fecal and tissue samples from sheep and cattle, over 25% of which contained viable MAP. Discrepant results for clinical samples between the two media were mostly associated with samples that contained fewer than 10 viable bacilli per gram, but were relatively uncommon and the performance of the two media was not significantly different. M7H9C medium was less than half the cost of BACTEC 12B medium, did not require regular examination during incubation, but a confirmatory IS900 PCR test had to be performed on every culture after the predetermined incubation period.
    Journal of clinical microbiology 09/2013; · 4.16 Impact Factor
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    ABSTRACT: Ovine Johne's disease (OJD) is a degenerative wasting condition of ruminants caused by Mycobacterium avium subsp. paratuberculosis (MAP). Similar to other pathogenic mycobacterial infections it is a slow-progressing chronic disease and subclinically infected individuals can spread the disease while appearing healthy. MAP infects macrophages and the host responds by mounting a cell-mediated immune response. Disease progression is associated with immune dysfunction but the reasons are unknown. Increasing our current knowledge of the immunological mechanisms involved in disease progression, including apoptotic responses, may allow advancements in the area of early diagnosis, identification of resistant animals and disease control. We describe lymphocyte apoptosis in peripheral blood mononuclear cells (PBMC) and lymph node cells from sheep exposed to MAP as well as from healthy non-exposed sheep. Apoptosis in intestinal lymph node cells from MAP-exposed infected sheep, but not in MAP-exposed uninfected sheep, increased in response to MAP antigen. In this first longitudinal study of lymphocyte apoptosis using an experimental infection model of MAP infection, we found that there was a transient increase of ex vivo PBMC apoptosis in MAP-exposed sheep soon after exposure to MAP (4 months post inoculation). MAP antigen-specific apoptosis occurred later, at 12 months post inoculation. The cells involved were mainly γδ and CD4(+) T cells. Antigen-mediated lymphocyte apoptosis during mycobacterial disease progression could contribute to the immune dysfunction in Johne's disease.
    Veterinary Immunology and Immunopathology 09/2013; · 1.88 Impact Factor
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    ABSTRACT: Johne's disease (JD) caused by Mycobacterium avium subspecies paratuberculosis (MAP) is a chronic infectious disease of ruminants. Activation of the Toll-like receptors (TLR) in response to microbial stimuli, including MAP, initiates responses in immune cells of the blood and within peripheral tissues. TLR2, 4 and 9 are believed to play a critical role in the initiation of immune responses against mycobacteria. In this study we report on the in vivo expression pattern of these receptors in sheep and cattle experimentally exposed to MAP. Experiments using the mouse macrophage cell line, RAW 264.7, and on isolated bovine monocytes were also carried out to assess the expression pattern of TLR2 and 4 in response to MAP and the non-pathogenic mycobacterial strain, M. smegmatis. Results from the in vivo study showed that there was a significant upregulation of TLR2 (P<0.05) at early time-points post-inoculation in the peripheral blood cells of sheep exposed to MAP S strain that went on to develop severe (multibacillary) disease. However, in the cattle during the initial months post-exposure to MAP C strain, TLR2 was significantly downregulated (P<0.05). TLR4 was significantly upregulated (P<0.05) at later stages (12 months post-inoculation) in MAP-exposed sheep with multibacillary disease; however significant differences in TLR4 expression were not observed in cattle. Expression of TLR9 was unchanged in MAP-exposed sheep and cattle. In vitro studies on mouse macrophages supported the findings of in vivo TLR2 gene expression increases seen in the sheep, in that the TLR2 receptor expression in response to MAP-infection was significantly increased in comparison to cells infected with a non-virulent mycobacterium, M. smegmatis. A likely role for TLR2 in the pathogenesis of Johne's disease is proposed.
    Veterinary Immunology and Immunopathology 08/2013; · 1.88 Impact Factor
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    ABSTRACT: Diagnostic tests used for Johne's disease in sheep either have poor sensitivity and specificity or only detect disease in later stages of infection. Predicting which of the infected sheep are likely to become infectious later in life is currently not feasible and continues to be a major hindrance in disease control. We conducted this longitudinal study to investigate if a suite of diagnostic tests conducted in Mycobacterium avium subspecies paratuberculosis (MAP) exposed lambs at 4 months post infection can accurately predict their clinical status at 12 months post infection. We tracked cellular and humoral responses and quantity of MAP shedding for up to 12 months post challenge in 20 controls and 37 exposed sheep. Infection was defined at necropsy by tissue culture and disease spectrum by lesion type. Data were analysed using univariable and multivariable logistic regression models and a subset of variables from the earliest period post inoculation (4 months) was selected for predicting disease outcomes later on (12 months). Sensitivity and specificity of tests and their combinations in series and parallel were determined. Early elevation in faecal MAP DNA quantity and a lower interferon gamma (IFNγ) response were significantly associated with sheep becoming infectious as well as progressing to severe disease. Conversely, early low faecal MAP DNA and higher interleukin-10 responses were significantly associated with an exposed animal developing protective immunity. Combination of early elevated faecal MAP DNA or lower IFNγ response had the highest sensitivity (75%) and specificity (81%) for identifying sheep that would become infectious. Collectively, these results highlight the potential for combined test interpretation to aid in the early prediction of sheep susceptibility to MAP infection.
    Preventive Veterinary Medicine 08/2013; · 2.39 Impact Factor
  • Ika Paul-Pont, Navneet K. Dhand, Richard J. Whittington
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    ABSTRACT: In 2010 Ostreid herpesvirus-1 (OsHV-1) was detected in Australia and had a disastrous impact on Pacific oyster Crassostrea gigas aquaculture and coastal communities. The acronymPOMS (Pacific OysterMortality Syndrome) was created in Australia to refer to mass mortalities due to OsHV-1. While management of this disease mainly involves active surveillance, rigorous biosecurity protocols and mollusc breeding programs targeting production of resistant animals, the effects of aquaculture practices on mortality outbreaks are still poorly understood. The present study aimed to determine the effect of growing heights on OsHV-1 associated mortality in C. gigas in Woolooware Bay (Australia) during the summer 2011/2012. Growing height influences the immersion time of inter-tidally cultivated oysters during each tide cycle, and could be an important risk factor for OsHV-1 exposure and mortality. Pacific oysters of different ages (2 and 12 month) were placed in intertidal rearing structures at three different sites in the bay. Mortality and growth rates, infection prevalence and seawater parameters (temperature and salinity) were monitored over 7 months. The outbreak started in November 2011 and mortalities were observed until late April 2012. The pattern of disease expression was time and site dependent as the mortalities started immediately after infection with OsHV-1 at two of the three sites, while the infection preceded the onset of mortality by two months at the third site. No clear difference in salinity or temperature of water was observed among sites suggesting that other environmental features influence the onset of the disease. Extreme mortalities were observed in the younger class of oysters, while the modification of growing height led to a significant increase in survival of adult oysters. Infection prevalence and intensity decreased in surviving oysters suggesting that some individuals may be able to clear the virus. Differences in mortality among sites and growing heights are discussed in relation to OsHV-1 infection intensity and prevalence in oysters, and the environmental data recorded during the outbreak.
    Aquaculture 07/2013; 412-413:202-214. · 2.01 Impact Factor
  • Ika Paul-Pont, Navneet K Dhand, Richard J Whittington
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    ABSTRACT: The ostreid herpesvirus OsHV-1 has the potential to devastate Pacific oyster 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 3 different locations at 3 different tidal levels, and OsHV-1 associated mortalities were closely monitored over 7 mo. 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 a common 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 regard to factors known to influence mechanism of disease transmission in aquatic environments (hydrodynamics, physical disturbances, host density/distribution, and variations of environmental parameters). A new hypothesis proposing that OsHV-1 may be carried through water by particles, possibly plankton, is also suggested to explain the patchy distribution of mortalities in Woolooware Bay.
    Diseases of Aquatic Organisms 07/2013; 105(2):127-38. · 1.73 Impact Factor
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    Ratna B Gurung, Douglas J Begg, Auriol C Purdie, Richard J Whittington
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    ABSTRACT: Serum antibody enzyme-linked immunosorbent assay is the most commonly used test for diagnosis of Mycobacterium avium subsp. paratuberculosis infection in ruminants. However, the assay requires serum preabsorption with Mycobacterium phlei proteins to reduce cross reactions potentially contributed by the exposure of livestock to environmental mycobacteria. To trial the discovery of novel antigens which do not require serum absorption, synthetic MAP-specific peptides were selected based on in silico research to identify putative B cell epitopes. Four peptides from previously identified stress-regulated proteins were synthesized and evaluated using enzyme linked immunosorbent assay to detect Mycobacterium avium subsp. paratuberculosis specific antibodies in sheep. Two peptides were from hypothetical MAP proteins (MAP3567 and MAP1168c) and two were from proteins with known function (MAP2698c, an acyl-acyl carrier protein desaturase-DesA2 and MAP2487c a carbonic anhydrase). The ability of each peptide to discriminate between unexposed and MAP exposed (infected and vaccinated) animals was similar to that of the parent recombinant MAP antigen, with area under receiver operating curve values of 0.86-0.93. Assays run with a combination of two peptides showed slightly higher reactivity than those of individual peptides. Peptides evaluated in this study had diagnostic potential similar to corresponding recombinant proteins but not superior to a complex native MAP antigen or a commercial assay. Further study is required to investigate other peptides for their diagnostic potential, and this may be simpler and cheaper than subunit protein-based research.
    Veterinary Immunology and Immunopathology 06/2013; · 1.88 Impact Factor
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    ABSTRACT: This study was conducted to evaluate the effectiveness of Gudair™ vaccine in decreasing the prevalence of shedding of Mycobacterium avium subsp. paratuberculosis (MAP) in flocks of varying initial prevalence. Thirty-seven self-replacing Merino flocks from New South Wales and Victoria (Australia) that had been vaccinating lambs with Gudair™ for at least five years were enrolled in the study. These flocks had been tested prior to or at commencement of vaccination using pooled faecal culture, agar gel immunodiffusion or both tests. These pre-vaccination test results were used to estimate pre-vaccination prevalence. Post-vaccination prevalence was estimated from culture of usually 7 pools of 50 sheep collected from the enrolled flocks in 2008-2009, approximately five or more years after commencement of vaccination. A Bayesian model was developed to estimate and compare the pre- and post-vaccination prevalences for the enrolled flocks. Apparent pre- and post-vaccination prevalences for flocks were modelled as functions of the true pre- and post-vaccination prevalences, respectively, and the sensitivities and specificities of the respective diagnostic tests. Logit-normal models were specified on pre- and post-vaccination true prevalences and were then used to make inferences about the median and 90th percentile of the prevalence distributions and their differences. Priors were mostly specified based on published literature or analysis of abattoir surveillance data for this population of flocks. The analysis found a significant decline in ovine Johne's disease prevalence from a pre-vaccination median prevalence of 2.72% [95% probability interval (PI): 1.40; 6.86%] to a post-vaccination median prevalence of 0.72% (0.39; 1.27%). However 30 of the 37 flocks still contained sheep that were shedding MAP in their faeces. The results suggest that vaccination with Gudair™ is usually effective in reducing the prevalence of faecal shedding but the response to vaccination is variable among flocks. The Bayesian approach reported here could be implemented in similar situations to compare prevalences where information from multiple diagnostic tests with varied sensitivities and specificities is available.
    Preventive Veterinary Medicine 04/2013; · 2.39 Impact Factor

Publication Stats

3k Citations
463.96 Total Impact Points

Institutions

  • 1996–2013
    • University of Sydney
      • Faculty of Veterinary Science
      Sydney, New South Wales, Australia
  • 2010
    • New South Wales Department of Primary Industries
      Орандж, New South Wales, Australia
    • Colorado State University
      • Animal Population Health Institute
      Fort Collins, CO, United States
  • 2003–2010
    • Monash University (Australia)
      • • Department of Biochemistry and Molecular Biology
      • • ARC Centre of Excellence in Structural and Functional Microbial Genomics
      • • Department of Microbiology
      Melbourne, Victoria, Australia
  • 1992–2009
    • Elizabeth Macarthur Agricultural Institute
      Cambelltown, South Australia, Australia
  • 2008
    • Department of Fisheries, Western Australia
      Perth City, Western Australia, Australia
  • 2004
    • Royal Veterinary College
      Londinium, England, United Kingdom
  • 2001
    • University of Pennsylvania
      • School of Veterinary Medicine
      Philadelphia, PA, United States
  • 1998
    • Australian Animal Health Laboratory
      Geelong, Victoria, Australia