Statistical physics of vaccination

Historically, infectious diseases caused considerable damage to human societies, and they continue to do so today. To help reduce their impact, mathematical models of disease transmission have been studied to help understand disease dynamics and inform prevention strategies. Vaccination–one of the most important preventive measures of modern times–is of great interest both theoretically and empirically. And in contrast to traditional approaches, recent research increasingly explores the pivotal implications of individual behavior and heterogeneous contact patterns in populations. Our report reviews the developmental arc of theoretical epidemiology with emphasis on vaccination, as it led from classical models assuming homogeneously mixing (mean-field) populations and ignoring human behavior, to recent models that account for behavioral feedback and/or population spatial/social structure. Many of the methods used originated in statistical physics, such as lattice and network models, and their associated analytical frameworks. Similarly, the feedback loop between vaccinating behavior and disease propagation forms a coupled nonlinear system with analogs in physics. We also review the new paradigm of digital epidemiology, wherein sources of digital data such as online social media are mined for high-resolution information on epidemiologically relevant individual behavior. Armed with the tools and concepts of statistical physics, and further assisted by new sources of digital data, models that capture nonlinear interactions between behavior and disease dynamics offer a novel way of modeling real-world phenomena, and can help improve health outcomes. We conclude the review by discussing open problems in the field and promising directions for future research

Studies on the biology of some parasites of the three-spined stickleback, Gasterosteus aculeatus L. with special reference to myxosporea

A population of three-spined stickleback, Gasterosteus aculeatus L., was sampled every two weeks for 14 months from Airthrey Loch on the campus of the University of Stirling. A total of 857 fish were collected and three species of parasites were studied. The monogenean Gyrodactylus gasterostei was found on the skin and fins and two myxosporean parasites, Sphaerospora elegans and Myxobilatus gasterostei, were present in the kidney. All parasite species were present throughout the year but abundance was correlated with the yearly life cycle of the host fish. Lower prevalence and intensity were observed in summer due to the large number of young fish in the samples. The comparative ultrastructure and development of the two myxosporeans was studied by light and transmission and scanning electron microscopy. Both myxosporeans followed the general pattern of myxosporean development but showed some novel features. Sphaerospora e/egans had two distinct developmental cycles. A proliferative cycle involving extrasporogonic stages occurred in the blood whereas spore production occurred in the kidney. Light microscopy of Giemsa stained blood smears suggested proliferation of extra-sporogonic stages by external budding or plasmotomy. Structural similarities between extra-sporogonic blood stages and sporogonic kidney stages are discussed. Although S. elegans mostly formed disporous plasmodia, monosporous plasmodia were also occasionally observed. Before the appearance of sporogonic cells within the early pseudoplasmodia, certain areas of pseudoplasmodial cytoplasm became electron lucent, eventually acquired cell organeUes and later appeared as sporogonic cells. Developing valvogenic cells contained protuberances at the posterolateral side of spores which disappeared in mature spores. Characteristic lipid bodies were seen in developing capsulogenic cells and developing uninucleated sporoplasmic cells contained abundant glycogen granules. The sporoplasmic cells were devoid of sporoplasmosomes. Plasmodia of M. gasterostei were mono, di or polysporous and showed features of both coelozoic and histozoic myxosporeans, including a unit surface membrane, simple pinocytosis aanand presence of a number of vegetative nuclei and generative cells, the latter which formed pansporoblasts before the initiation of sporogenesis. A membrane bound tubular structure and some electron dense fibrillar bundles are previously undiscovered cytoplasmic organelles of the plasmodia. Developing capsulogenic cells contained characteristic membrane bound vacuoles filled with electron dense (glycogen) material. Myxobilatus gasterostel attached to the epithelial cells by plasmodial surface projections and there were electron dense areas at the point of attachment. Sphaerospora elegans showed occasional hairlike processes projecting from the pseudoplasmodial surface to the microvillous brush border of the epithelial cells. There were no electron dense areas at the point of attachment to the epithelial cells of the kidney tubules. Early undifferentiated pre-sporogonic stages of both parasites were occasionally present intracellularly in the tubular epithelium suggesting this is a route of entry into the tubular lumen. Early stages of S. elegans were also seen in the capillary lumen of the glomerulus. Intracellular and intraluminal stages of S. elegans and M. gasterostel caused pathological changes in different ways. Histopathological changes associated with S. elegans included vacuolation and accumulation of electron dense material in the epithelium whereas M. gasterostei caused large vacuolation with necrosis of the epithelial layer. Both parasites caused destruction of glomerular tufts in heavy infections and an increased number of rodlet cells in the epithelial layer were common in both cases. The two myxosporean species were most abundant during the winter and spring. Extra-sporogonic stages of S. elegans were found only in January and June in the rete-mirabile of the eye, circulating blood and kidney. In infections with S. elegans sex of the host fish was apparently of no significance, whereas significantly lower infestations occurred in male sticklebacks infected with M. gasterostei compared with females. Host size was important in determining the prevalence and intensity of both myxosporean species. Older fish were less heavily infected, possibly due to an acquired immunity or pathogenic effects on the host. A high number of mixed infections indicated that there was no interspeciflc competition between the two parasites. There appeared to be a continuous recruitment of myxosporeans throughout the year. Studies on myxosporean spore shedding suggested that spore production and shedding was continuous throughout the year and was uninfluenced by temperature or season. Gyrodactylus gasterostel was generally more abundant in winter and spring than in summer and autumn, reflecting the greater numbers of small young of the year fish at these times. The age of the host fish was a significant factor influencing the prevalence and intensity of infestation with G. gasterostei. Sex of the host had no apparent influence on infestation. The parasite was highly overdispersed within the host population and its distribution was best fitted by the negativ

Predictive modelling of climate change impacts on disease dynamics in Tanzania

Climate and the environment are key determinants impacting various aspects of disease transmission, including lifecycle, survivability and prevalence. Recent changes in both the long-term climatology, and short term El Niño events are impacting the spatial distribution of disease, increasing the number of people being at higher risk of contracting fatal diseases. These changes are particularly detrimental in developing countries, where socioeconomic conditions hinder access to disease prevention and treatment. This thesis explores climate, environment and disease interactions using multiple epidemiological modelling methodologies to develop an informative framework within which disease risk can be assessed, to aid decision-making. Statistical analysis of the impact of extreme events indicate that El Niño has a significant impact on the Tanzanian climate, which differs by location. Spatial modelling results demonstrate that by 2050 under RCP 8.5 mean malaria risk will initially reduce by 4.7%, which then reverses to an increase of 8.9% in 2070. Overall, analysis indicates increases in mean malaria risk. Biological modelling indicates that the predicted increases in malaria risk are likely a result of the reduction in time taken to complete the sporogonic and gonotrophic cycles due to increasingly optimum environmental conditions. The novel approach applied here contributes the development of a new model in environmental epidemiology. This thesis concludes that epidemiological modelling results could be beneficial in aiding decision makers to prepare for the impact of climate and environmental change, with a recommendation to continue research in this area with a particular focus on understudied and developing countries

The role of visual adaptation in cichlid fish speciation

D. Shane Wright (1) , Ole Seehausen (2), Ton G.G. Groothuis (1), Martine E. Maan (1) (1) University of Groningen; GELIFES; EGDB(2) Department of Fish Ecology & Evolution, EAWAG Centre for Ecology, Evolution and Biogeochemistry, Kastanienbaum AND Institute of Ecology and Evolution, Aquatic Ecology, University of Bern.In less than 15,000 years, Lake Victoria cichlid fishes have radiated into as many as 500 different species. Ecological and sexual sel ection are thought to contribute to this ongoing speciation process, but genetic differentiation remains low. However, recent work in visual pigment genes, opsins, has shown more diversity. Unlike neighboring Lakes Malawi and Tanganyika, Lake Victoria is highly turbid, resulting in a long wavelength shift in the light spectrum with increasing depth, providing an environmental gradient for exploring divergent coevolution in sensory systems and colour signals via sensory drive. Pundamilia pundamila and Pundamilia nyererei are two sympatric species found at rocky islands across southern portions of Lake Victoria, differing in male colouration and the depth they reside. Previous work has shown species differentiation in colour discrimination, corresponding to divergent female preferences for conspecific male colouration. A mechanistic link between colour vision and preference would provide a rapid route to reproductive isolation between divergently adapting populations. This link is tested by experimental manip ulation of colour vision - raising both species and their hybrids under light conditions mimicking shallow and deep habitats. We quantify the expression of retinal opsins and test behaviours important for speciation: mate choice, habitat preference, and fo raging performance

Mesophilic Aeromonas in threatened Iberian leuciscids : conservation and public health implications

Tese de Doutoramento em Ciências Veterinárias na Especialidade de Sanidade AnimalDespite the high risk of extinction of the Iberian leuciscids, the impact of bacterial diseases on their conservation is unknown. A comprehensive knowledge of the interaction between these species and pathogens, such as mesophilic Aeromonas, as well as the development of biosafety measures for ex situ programs, are considered essential for the success of their conservation. The main objectives of this thesis are the evaluation of the epidemiology of mesophilic Aeromonas in Iberochondrostoma lusitanicum, as well as the characterization of their antimicrobial resistance and virulence profiles, the detection of differences in the diversity of Aeromonas spp. of I. lusitanicum and Squalius pyrenaicus, the evaluation of the potential of biosecurity measures in the control of Aeromonas spp. in ex situ programs and testing the effect of climate change on Aeromonas spp. The results showed that I. lusitanicum presented lower general health status in the dry season, varying with location. Aeromonas communities varied between seasons and locations, while their pathogenic potential increased in the dry season. Relevant resistance phenotypes (carbapenems and fluoroquinolones) were detected. Furthermore, I. lusitanicum and S. pyrenaicus showed different levels of skin lesions, with S. pyrenaicus being the most affected species. Aeromonas communities differed between the two fish species. Additionally, the use of biosecurity measures suggests a decrease in the prevalence of Aeromonas spp. in ex situ programs, as well as its pathogenicity to fish, while an increase in antimicrobial resistance was observed throughout the program. Finally, climate change predicted by the International Panel on Climate Change for water temperature and pH influenced the growth, biofilm production and antimicrobial resistance profiles of Aeromonas spp. The current results clarify the epidemiology of mesophilic Aeromonas in threatened Iberian leuciscids and contribute to the establishment of adequate conservation measures.RESUMO - Apesar do elevado risco de extinção dos leuciscídeos ibéricos, desconhece-se o impacto das doenças bacterianas na sua conservação. Um conhecimento abrangente sobre a interação entre estas espécies e agentes patogénicos, como Aeromonas mesofílicas, bem como o desenvolvimento de medidas de biossegurança para programas ex situ, são considerados essenciais para o sucesso da sua conservação. Os principais objetivos desta tese são a avaliação da epidemiologia de Aeromonas mesofílicas em Iberocondrostoma lusitanicum, bem como a caracterização dos seus perfis de resistência antimicrobiana e virulência, a deteção de diferenças na diversidade de Aeromonas spp. de I. lusitanicum e Squalius pyrenaicus, a avaliação do potencial de medidas de biossegurança no controlo de Aeromonas spp. em programas ex situ e a testagem do efeito de alterações climáticas em Aeromonas spp. Os resultados mostraram que I. lusitanicum apresentaram estado geral de saúde inferior na época seca, variando com a localização. As comunidades de Aeromonas variaram entre épocas e localizações, enquanto o seu potencial patogénico aumentou na época seca. Foram detetados fenótipos de resistência relevantes (carbapenemos e fluroquinolonas). Além disso, I. lusitanicum e S. pyrenaicus apresentaram diferentes níveis de lesões cutâneas, sendo S. pyrenaicus a espécie mais afetada. As comunidades de Aeromonas diferiram entre as duas espécies de peixes. Adicionalmente, o uso de medidas de biossegurança sugere uma diminuição na prevalência de Aeromonas spp. em programas ex situ, bem como da sua patogenicidade para peixes, enquanto foi observado um aumento da resistência antimicrobiana ao longo do programa. Finalmente, as alterações climatéricas previstas pelo Painel Internacional sobre Mudanças Climáticas para a temperatura e pH da água influenciaram o crescimento, a produção de biofilme e os perfis de resistência antimicrobiana de Aeromonas spp. Os resultados atuais esclarecem sobre a epidemiologia de Aeromonas mesofílicas em leuciscídeos ibéricos ameaçados e contribuem para o estabelecimento de medidas de conservação adequadasN/

Stochastic Periodic Solution of a Susceptible-Infective Epidemic Model in a Polluted Environment under Environmental Fluctuation

It is well known that the pollution and environmental fluctuations may seriously affect the outbreak of infectious diseases (e.g., measles). Therefore, understanding the association between the periodic outbreak of an infectious disease and noise and pollution still needs further development. Here we consider a stochastic susceptible-infective (SI) epidemic model in a polluted environment, which incorporates both environmental fluctuations as well as pollution. First, the existence of the global positive solution is discussed. Thereafter, the sufficient conditions for the nontrivial stochastic periodic solution and the boundary periodic solution of disease extinction are derived, respectively. Numerical simulation is also conducted in order to support the theoretical results. Our study shows that (i) large intensity noise may help the control of periodic outbreak of infectious disease; (ii) pollution may significantly affect the peak level of infective population and cause adverse health effects on the exposed population. These results can help increase the understanding of periodic outbreak patterns of infectious diseases