The Effects of Spatio-Temporal Heterogeneities on the Emergence and Spread of Dengue Virus

The dengue virus (DENV) remains a considerable global public health concern. The interactions between the virus, its mosquito vectors and the human host are complex and only partially understood. Dependencies of vector ecology on environmental attributes, such as temperature and rainfall, together with host population density, introduce strong spatiotemporal heterogeneities, resulting in irregular epidemic outbreaks and asynchronous oscillations in serotype prevalence. Human movements across different spatial scales have also been implicated as important drivers of dengue epidemiology across space and time, and further create the conditions for the geographic expansion of dengue into new habitats. Previously proposed transmission models often relied on strong, unrealistic assumptions regarding key epidemiological and ecological interactions to elucidate the effects of these spatio-temporal heterogeneities on the emergence, spread and persistence of dengue. Furthermore, the computational limitations of individual based models have hindered the development of more detailed descriptions of the influence of vector ecology, environment and human mobility on dengue epidemiology. In order to address these shortcomings, the main aim of this thesis was to rigorously quantify the effects of ecological drivers on dengue epidemiology within a robust and computational efficient framework. The individual based model presented included an explicit spatial structure, vector and human movement, spatio-temporal heterogeneity in population densities, and climate effects. The flexibility of the framework allowed robust assessment of the implications of classical modelling assumptions on the basic reproduction number, R₀, demonstrating that traditional approaches grossly inflate R₀ estimates. The model's more realistic meta-population formulation was then exploited to elucidate the effects of ecological heterogeneities on dengue incidence which showed that sufficient levels of community connectivity are required for the spread and persistence of dengue virus. By fitting the individual based model to empirical data, the influence of climate and on dengue was quantified, revealing the strong benefits that cross-sectional serological data could bring to more precisely inferring ecological drivers of arboviral epidemiology. Overall, the findings presented here demonstrate the wide epidemiological landscape which ecological drivers induce, forewarning against the strong implications of generalising interpretations from one particular setting across wider spatial contexts. These findings will prove invaluable for the assessment of vector-borne control strategies, such as mosquito elimination or vaccination deployment programs

Scattering and Iron Fluorescence Revealed During Absorption Dips in Circinus X-1

We show that dramatic spectral evolution associated with dips occurring near phase zero in RXTE observations of Cir X-1 is well-fit by variable and at times heavy absorption (N_H > 10^24 cm^-2) of a bright component, plus an underlying faint component which is not attenuated by the variable column and whose flux is ~10% of that of the unabsorbed bright component. A prominent Fe emission line at ~6.5 keV is evident during the dips. The absolute line flux outside the dips is similar to that during the dips, indicating that the line is associated with the faint component. These results are consistent with a model in which the bright component is radiation received directly from a compact source while the faint component may be attributed to scattered radiation. Our results are also generally consistent with those of Brandt et al., who found that a partial- covering model could explain ASCA spectra of a low-to-high transition in Cir X-1. The relative brightness of the two components in our model requires a column density of ~2*10^23 cm^-2 if the faint component is due to Thomson scattering in material that mostly surrounds the source. We find that illumination of such a scattering cloud by the observed direct component would produce an Fe K-alpha fluorescence flux that is in rough agreement with the flux of the observed emission line. We also conclude that if the scattering medium is not highly ionized, our line of sight to the compact source does not pass through it. Finally, we discuss simple pictures of the absorbers responsible for the dips themselves.Comment: Accepted for publication in The Astrophysical Journal (23 pages, including 11 figures

Stochastic parameterization: uncertainties from convection

In 2005, the ECMWF held a workshop on stochastic parameterisation, at which the convection was seen as being a key issue. That much is clear from the working group reports and particularly the statement from working group 1 that “it is clear that a stochastic convection scheme is desirable”. The present note aims to consider our current status in comparison with some of the issues raised and hopes expressed in that working group report

BITING OFF MORE MAN ONE CAN CHEW: A RECENT TREND IN THE INTERPRETATION OF JUVENAL'S 15TH SATIRE

In his discussion of Juvenal's 15th Satire, entitled "Philosophers and Cannibals", Richard McKim (1986:58) observes that the poem "has traditionally been an object of distaste and neglect".1 He describes the tirade against the Egyptians as "a tissue of hysterical racism, stupid morbidity, and smug self-congratulation" and concludes that "on the traditional assumption of identity between the Satire's first-person bigot and its author, it seems merely another unpleasant document in the history of bigotry". McKim endeavours to give a more palatable interpretation of the Satire's purpose, and scope for this is provided by the dichotomy which the persona-theory postulates between the author and his "speaker". Rejecting the assumption that Juvenal is giving expression to his own views, he suggests that Juvenal is presenting the character of his "speaker" to the reader for critical inspection and that his intention is to direct the reader's scorn "not against the Egyptians whom his speaker is attacking but against the speaker himself for his delusion that Roman society is superior" (McKim 1986:59)

Robustness of the reproductive number estimates in vector-borne disease systems

This is the final version. Available on open access from Public Library of Science via the DOI in this recordData Availability: All relevant data are within the paper and its Supporting Information files.Background: The required efforts, feasibility and predicted success of an intervention strategy against an infectious disease are partially determined by its basic reproduction number, R0. In its simplest form R0 can be understood as the product of the infectious period, the number of infectious contacts and the per-contact transmission probability, which in the case of vector-transmitted diseases necessarily extend to the vector stages. As vectors do not usually recover from infection, they remain infectious for life, which places high significance on the vector’s life expectancy. Current methods for estimating the R0 for a vector-borne disease are mostly derived from compartmental modelling frameworks assuming constant vector mortality rates. We hypothesised that some of the assumptions underlying these models can lead to unrealistic high vector life expectancies with important repercussions for R0 estimates. Methodology and principal findings: Here we used a stochastic, individual-based model which allowed us to directly measure the number of secondary infections arising from one index case under different assumptions about vector mortality. Our results confirm that formulas based on age-independent mortality rates can overestimate R0 by nearly 100% compared to our own estimate derived from first principles. We further provide a correction factor that can be used with a standard R0 formula and adjusts for the discrepancies due to erroneous vector age distributions. Conclusion: Vector mortality rates play a crucial role for the success and general epidemiology of vector-transmitted diseases. Many modelling efforts intrinsically assume these to be age-independent, which, as clearly demonstrated here, can lead to severe over-estimation of the disease’s reproduction number. Our results thus re-emphasise the importance of obtaining field-relevant and species-dependent vector mortality rates, which in turn would facilitate more realistic intervention impact predictions.Engineering and Physical Sciences Research Council (EPSRC

REFLECTIONS ON A MIRROR: POSSIBLE EVIDENCE FOR THE EARLY ORIGIN OF THE CANONICAL VERSION OF THE ROMAN FOUNDATION LEGEND

T.P. Wiseman (1991: 115-124) suggests that the whole story of the twins - and in particular the life and death of Remus - was progressively invented between the Lex Licinia Sextia in 367 and the battle of Sentinum in 295, a period which "saw the establishment of a new mythology, a new way of making sense of Rome and her destiny in an era of cataclysmic change".1 Wiseman has not beel) the only scholar to postulate a relatively late development of the Romulus and Remus legend: H. Strasburger (1968) argued that it was created during the last decades of the 4th century or, more probably, during the first decades of the 3rd. Furthermore, he maintained that, because the tale contained elements - notably that of fratricide - which did not reflect favourably on the image of Rome, it was essentially the product of anti-Roman propaganda. Wiseman, on the other hand, suggests that Remus represents the Roman plebs and that the twins actually symbolise the "power-sharing" between patricians and plebeians brought about by the Licinio-Sextian laws. The starting point of Wiseman's thesis is that the plebs' "lateness" in coming to power is reflected in the name "Remus", which signifies "slowness"; and he cites the etymology given in the Origo Gentis Romanae (21.5), where "Romulus" is derived from "rhome" ("strength") and "Remus" from "remores", because that is what the ancients called people who were "slow" by nature