451 research outputs found
Immunogenicity and protective efficacy of an anti-Streptococcus pyogenes vaccine candidate in multiple animal species
Streptococcus pyogenes, also known as Group A Streptococcus (GAS) has been associated with a range of diseases from the mild pharyngitis and pyoderma to more severe invasive infections such as streptococcal toxic shock. GAS also causes a number of non-suppurative post-infectious diseases such as rheumatic fever, rheumatic heart disease and glomerulonephritis. The large extent of GAS disease burden necessitates the need for a prophylactic vaccine that could target the diverse GAS emm types circulating globally. Anti-GAS vaccine strategies have focused primarily on the GAS M-protein, an extracellular virulence factor anchored to GAS cell wall. As opposed to the hypervariable N-terminal region, the C-terminal portion of the protein is highly conserved among different GAS emm types and is the focus of a leading GAS vaccine candidate, J8-DT/alum. The vaccine candidate J8-DT/alum was shown to be immunogenic in mice, rabbits and the non-human primates, hamadryas baboons. Similar responses to J8-DT/alum were observed after subcutaneous and intramuscular immunization with J8-DT/alum, in mice and in rabbits. Further assessment of parameters that may influence the immunogenicity of J8-DT demonstrated that the immune responses were identical in male and female mice and the use of alum as an adjuvant in the vaccine formulation significantly increased its immunogenicity, resulting in a long-lived serum IgG response. Contrary to the previous findings, the data in this thesis indicates that a primary immunization with J8-DT/alum (50ƒÊg) followed by a single boost is sufficient to generate a robust immune response in mice. As expected, the IgG response to J8- DT/alum was a Th2 type response consisting predominantly of the isotype IgG1 accompanied by lower levels of IgG2a. Intramuscular vaccination of rabbits with J8-DT/alum demonstrated that an increase in the dose of J8-DT/alum up to 500ƒÊg does not have an impact on the serum IgG titers achieved. Similar to the immune response in mice, immunization with J8-DT/alum in baboons also established that a 60ƒÊg dose compared to either 30ƒÊg or 120ƒÊg was sufficient to generate a robust immune response. Interestingly, mucosal infection of naive baboons with a M1 GAS strain did not induce a J8-specific serum IgG response. As J8-DT/alum mediated protection has been previously reported to be due to the J8- specific antibody formed, the efficacy of J8-DT antibodies was determined in vitro and in vivo. In vitro opsonization and in vivo passive transfer confirmed the protective potential of J8-DT antibodies. A reduction in the bacterial burden after challenge with a bioluminescent M49 GAS strain in mice that were passively administered J8-DT IgG established that protection due to J8-DT was mediated by antibodies. The GAS burden in infected mice was monitored using bioluminescent imaging in addition to traditional CFU assays. Bioluminescent GAS strains including the ‘rheumatogenic’ M1 GAS could not be generated due to limitations with transformation of GAS, however, a M49 GAS strain was utilized during BLI. The M49 serotype is traditionally a ‘nephritogenic’ serotype associated with post-streptococcal glomerulonephritis. Anti- J8-DT antibodies now have been shown to be protective against multiple GAS strains such as M49 and M1. This study evaluated the immunogenicity of J8-DT/alum in different species of experimental animals in preparation for phase I human clinical trials and provided the ground work for the development of a rapid non-invasive assay for evaluation of vaccine candidates
Triggered fragmentation in gravitationally unstable discs: forming fragments at small radii
We carry out three dimensional radiation hydrodynamical simulations of
gravitationally unstable discs using to explore the movement of mass in a disc
following its fragmentation. Compared to a more quiescent state before it
fragments, the radial velocity of the gas increases by up to a factor of ~2-3
after fragmentation. While the mass movement occurs both inwards and outwards,
the inwards motion can cause the inner spirals to be sufficiently dense that
they may become unstable and potentially fragment. Consequently, the dynamical
behaviour of fragmented discs may cause subsequent fragmentation at smaller
radii after an initial fragment has formed in the outer disc.Comment: Submitted to the conference proceedings of: Instabilities and
Structures in Proto-Planetary Disks. 5 pages; 4 figure
Non-convergence of the critical cooling timescale for fragmentation of self-gravitating discs
We carry out a resolution study on the fragmentation boundary of
self-gravitating discs. We perform three-dimensional Smoothed Particle
Hydrodynamics simulations of discs to determine whether the critical value of
the cooling timescale in units of the orbital timescale, beta_{crit}, converges
with increasing resolution. Using particle numbers ranging from 31,250 to 16
million (the highest resolution simulations to date) we do not find
convergence. Instead, fragmentation occurs for longer cooling timescales as the
resolution is increased. These results suggest that at the very least, the
critical value of the cooling timescale is longer than previously thought.
However, the absence of convergence also raises the question of whether or not
a critical value exists. In light of these results, we caution against using
cooling timescale or gravitational stress arguments to deduce whether
gravitational instability may or may not have been the formation mechanism for
observed planetary systems.Comment: Accepted for publication by MNRAS Letters. 6 pages, 3 figure
Large grains can grow in circumstellar discs
We perform coagulation & fragmentation simulations to understand grain growth
in T Tauri & brown dwarf discs. We present a physically-motivated approach
using a probability distribution function for the collision velocities and
separating the deterministic & stochastic velocities. We find growth to larger
sizes compared to other models. Furthermore, if brown dwarf discs are
scaled-down versions of T Tauri discs (in terms of stellar & disc mass, and
disc radius), growth at the same location with respect to the outer edge occurs
to similar sizes in both discs.Comment: Submitted to the conference proceedings of the IAU Symposium 299 -
Exploring the formation and evolution of planetary systems. 2 pages; 2
figure
Island Dreaming: Applied Epidemiology in the Pacific Region
This bound volume describes four significant public health
problems in Australia and the Pacific Island Countries of Fiji
and American Samoa. The four main epidemiological components
are:
1) Australian vaccine preventable disease epidemiological review
series: varicella-zoster virus infections, 1998–2015. The
review was conducted to assess the impact of the national
varicella immunisation program and provide a baseline for
monitoring the impact of the national herpes zoster immunisation
program. The national varicella immunisation program led to
significant reductions in varicella. In Australia, the burden of
herpes zoster is substantial, and high quality and timely
surveillance will be crucial to assess the impact of the national
herpes zoster immunisation program.
2) Investigation into increased lymphogranuloma venereum (LGV) in
New South Wales, Australia. LGV is a sexually transmitted
infection (STI) caused by L1-L3 serovars of chlamydia, and can
lead to irreversible complications. LGV is notifiable condition
in New South Wales (NSW). Following a noticeable increase in
number of LGV notifications, I conducted a retrospective case
series of all cases diagnosed between 1 January 2016 and 31 March
2017. During this period, all reported cases were among men who
have sex with men. This chapter examines factors contributing to
increase in LGV cases in NSW in 2016. It also describes the
challenges associated with investigating STI outbreaks in NSW.
3) An evaluation of an early warning alert and response system
(EWARS in a Box) implemented after Cyclone Winston, Fiji 2016.
The World Health Organization recommends implementation of early
warning systems for timely disease surveillance and early
detection of outbreaks during humanitarian emergencies. This
chapter describes the EWARS system, and its usefulness at timely
monitoring of communicable diseases trends during a national
health emergency. Findings include strengths and limitations of
the system at conducting surveillance, along with practical
recommendations for improving surveillance using EWARS.
4) Identifying residual transmission of lymphatic filariasis in
post-mass drug administration surveillance phase: Comparing
school-based versus community-based surveys – American Samoa,
2016. This study compares the effectiveness of two
cross-sectional survey designs, a school-based and a
community-based survey, for assessing transmission of lymphatic
filariasis. Under the Global Programme for Elimination of
Lymphatic Filariasis, American Samoa conducted seven rounds of
mass drug administration (MDA) from 2000-2006. The World Health
Organization recommends systematic post-MDA surveillance for
epidemiological assessment of recent lymphatic filariasis
transmission. Finger prick blood samples were collected from
study participants to measure the prevalence of circulating
filarial antigen (CFA). I recruited 1143 grade 1 and 2 school
students from 29 elementary schools. For the community survey, 30
out of 70 villages were randomly selected, from which 2507
community members were recruited. The school survey was cheaper
and logistically easier to implement. The estimated CFA
prevalence by school survey was 0.7%, and was significantly lower
than the community survey (6.2%). The community survey was more
effective for collecting information required for identifying
residual transmission of lymphatic filariasis. Both surveys
provided evidence of ongoing lymphatic filariasis transmission in
American Samoa
On the gap-opening criterion of migrating planets in protoplanetary disks
We perform two-dimensional hydrodynamical simulations to quantitatively
explore the torque balance criterion for gap-opening (as formulated by Crida et
al. 2006) in a variety of disks when considering a migrating planet. We find
that even when the criterion is satisfied, there are instances when planets
still do not open gaps. We stress that gap-opening is not only dependent on
whether a planet has the ability to open a gap, but whether it can do so
quickly enough. This can be expressed as an additional condition on the
gap-opening timescale versus the crossing time, i.e. the time it takes the
planet to cross the region which it is carving out. While this point has been
briefly made in the previous literature, our results quantify it for a range of
protoplanetary disk properties and planetary masses, demonstrating how crucial
it is for gap-opening. This additional condition has important implications for
the survival of planets formed by core accretion in low mass disks as well as
giant planets or brown dwarfs formed by gravitational instability in massive
disks. It is particularly important for planets with intermediate masses
susceptible to Type III-like migration. For some observed transition disks or
disks with gaps, we expect that estimates on the potential planet masses based
on the torque balance gap-opening criterion alone may not be sufficient. With
consideration of this additional timescale criterion theoretical studies may
find a reduced planet survivability or that planets may migrate further inwards
before opening a gap.Comment: Accepted by ApJ, 22 pages, 13 figures, 6 table
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