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M Pawlikowski A Lewiński E Sewerynek M Szkudliński J Kunert-Radek E Wajs 《Biochemical and biophysical research communications》1990,166(3):1171-1175
The effects of a long-acting somatostatin analog SMS 201-995 injections on the basal and angiotensin II-stimulated [3H]-thymidine uptake by the rat adrenal glands incubated in vitro were examined. It was shown that SMS 201-995 significantly inhibited the [3H]-thymidine uptake and, additionally, suppressed the stimulatory effect of a single angiotensin II injection. 相似文献
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Assaf Zvuloni Yael Artzy-Randrup Guy Katriel Yossi Loya Lewi Stone 《PLoS computational biology》2015,11(6)
Coral reefs are in global decline, with coral diseases increasing both in prevalence and in space, a situation that is expected only to worsen as future thermal stressors increase. Through intense surveillance, we have collected a unique and highly resolved dataset from the coral reef of Eilat (Israel, Red Sea), that documents the spatiotemporal dynamics of a White Plague Disease (WPD) outbreak over the course of a full season. Based on modern statistical methodologies, we develop a novel spatial epidemiological model that uses a maximum-likelihood procedure to fit the data and assess the transmission pattern of WPD. We link the model to sea surface temperature (SST) and test the possible effect of increasing temperatures on disease dynamics. Our results reveal that the likelihood of a susceptible coral to become infected is governed both by SST and by its spatial location relative to nearby infected corals. The model shows that the magnitude of WPD epidemics strongly depends on demographic circumstances; under one extreme, when recruitment is free-space regulated and coral density remains relatively constant, even an increase of only 0.5°C in SST can cause epidemics to double in magnitude. In reality, however, the spatial nature of transmission can effectively protect the community, restricting the magnitude of annual epidemics. This is because the probability of susceptible corals to become infected is negatively associated with coral density. Based on our findings, we expect that infectious diseases having a significant spatial component, such as Red-Sea WPD, will never lead to a complete destruction of the coral community under increased thermal stress. However, this also implies that signs of recovery of local coral communities may be misleading; indicative more of spatial dynamics than true rehabilitation of these communities. In contrast to earlier generic models, our approach captures dynamics of WPD both in space and time, accounting for the highly seasonal nature of annual WPD outbreaks. 相似文献
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A spatial metapopulation is a mosaic of interconnected patch populations. The complex routes of colonization between the patches are governed by the metapopulation''s dispersal network. Over the past two decades, there has been considerable interest in uncovering the effects of dispersal network topology and its symmetry on metapopulation persistence. While most studies find that the level of symmetry in dispersal pattern enhances persistence, some have reached the conclusion that symmetry has at most a minor effect. In this work, we present a new perspective on the debate. We study properties of the in- and out-degree distribution of patches in the metapopulation which define the number of dispersal routes into and out of a particular patch, respectively. By analysing the spectral radius of the dispersal matrices, we confirm that a higher level of symmetry has only a marginal impact on persistence. We continue to analyse different properties of the in–out degree distribution, namely the ‘in–out degree correlation’ (IODC) and degree heterogeneity, and find their relationship to metapopulation persistence. Our analysis shows that, in contrast to symmetry, the in–out degree distribution and particularly, the IODC are dominant factors controlling persistence. 相似文献
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We study the attack rate, that is the total fraction of the population infected each year, for a disease with seasonally varying transmission rate. The attack rate is shown to be governed by both the reproductive number, reflecting the transmissibility of the disease, and the birth rate, which provides a source of new susceptibles. For the case of epidemics which have an annual period (like the seasonality), we prove inequalities which show that the attack rate is close to that of the non-seasonal model, so that it is nearly independent of the strength of the forcing, despite the fact that the shape of the epidemic curve depends strongly on the degree of seasonality of the forcing. Numerical simulations show that this holds to an even stronger extent than is implied by our rigorous results. When the system has subharmonic or chaotic solutions, we show that similar results hold when the attack rate is replaced by the average attack rate over several years. Consequences of these findings for analyzing the effect of vaccination in seasonally-forced models are noted. 相似文献
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Pulse vaccination strategy in the SIR epidemic model 总被引:34,自引:0,他引:34
Theoretical results show that the measles ‘pulse’ vaccination strategy can be distinguished from the conventional strategies
in leading to disease eradication at relatively low values of vaccination. Using the SIR epidemic model we showed that under
a planned pulse vaccination regime the system converges to a stable solution with the number of infectious individuals equal
to zero. We showed that pulse vaccination leads to epidemics eradication if certain conditions regarding the magnitude of
vaccination proportion and on the period of the pulses are adhered to. Our theoretical results are confirmed by numerical
simulations. The introduction of seasonal variation into the basic SIR model leads to periodic and chaotic dynamics of epidemics.
We showed that under seasonal variation, in spite of the complex dynamics of the system, pulse vaccination still leads to
epidemic eradication. We derived the conditions for epidemic eradication under various constraints and showed their dependence
on the parameters of the epidemic. We compared effectiveness and cost of constant, pulse and mixed vaccination policies. 相似文献