Ultra-violet radiation is responsible for the differences in global epidemiology of chickenpox and the evolution of varicella-zoster virus as man migrated out of Africa

<p>Abstract</p> <p>Background</p> <p>Of the eight human herpes viruses, varicella-zoster virus, which causes chickenpox and zoster, has a unique epidemiology. Primary infection is much less common in children in the tropics compared with temperate areas. This results in increased adult susceptibility causing outbreaks, for example in health-care workers migrating from tropical to temperate countries. The recent demonstration that there are different genotypes of varicella-zoster virus and their geographic segregation into tropical and temperate areas suggests a distinct, yet previously unconsidered climatic factor may be responsible for both the clinical and molecular epidemiological features of this virus infection.</p> <p>Presentation of the hypothesis</p> <p>Unlike other human herpes viruses, varicella-zoster virus does not require intimate contact for infection to occur indicating that transmission may be interrupted by a geographically restricted climatic factor. The factor with the largest difference between tropical and temperate zones is ultra-violet radiation. This could reduce the infectiousness of chickenpox cases by inactivating virus in vesicles, before or after rupture. This would explain decreased transmissibility in the tropics and why the peak chickenpox incidence in temperate zones occurs during winter and spring, when ultra-violet radiation is at its lowest. The evolution of geographically restricted genotypes is also explained by ultra-violet radiation driving natural selection of different virus genotypes with varying degrees of resistance to inactivation, tropical genotypes being the most resistant. Consequently, temperate viruses should be more sensitive to its effects. This is supported by the observation that temperate genotypes are found in the tropics only in specific circumstances, namely where ultra-violet radiation has either been excluded or significantly reduced in intensity.</p> <p>Testing the Hypothesis</p> <p>The hypothesis is testable by exposing different virus genotypes to ultra-violet radiation and quantifying virus survival by plaque forming units or quantitative mRNA RT-PCR.</p> <p>Implications of the hypothesis</p> <p>The ancestral varicella-zoster virus, most probably a tropical genotype, co-migrated with man as he left Africa approximately 200,000 years ago. For this virus to have lost the selective advantage of resistance to ultra-violet radiation, the hypothesis would predict that the temperate, ultra-violet sensitive virus should have acquired another selective advantage as an evolutionary trade-off. One obvious advantage could be an increased reactivation rate as zoster to set up more rounds of chickenpox transmission. If this were so, the mechanism responsible for resistance to ultra-violet radiation might also be involved in reactivation and latency. This could then provide the first insight into a genetic correlate of the survival strategy of this virus.</p

Thermal Overstability Of Hydromagnetic Surface-Waves

We investigate the effects of radiative heat losses and thermal conductivity on the hydromagnetic surface waves along a magnetic discontinuity in a plasma of infinite electrical conductivity. We show that the effects of radiative heat losses on such surface waves are appreciable only when values of the plasma pressure on the two sides of the discontinuity are substantially different. Overstability of a surface wave requires that the medium in which it gives larger first-order compression should satisfy the criterion of Field (1965). Possible applications of the study to magnetic discontinuities in solar corona are briefly discussed

Modelling majority and expert influences on opinion formation in online social networks

Two most important social influences that shape the opinion formation process are: (i) the majority influence caused by the existence of a large group of people sharing similar opinions and (ii) the expert influence originated from the presence of experts in a social group. When these two effects contradict each other in real life, they may pull the public opinions towards their respective directions. Existing models on opinion formation utilised the idea of expertise levels in conjunction with the expressed opinions of the agents to encapsulate the expert effect. However, they have disregarded the explicit consideration of the majority effect, and thereby failed to capture the concurrent and combined impact of these two influences on opinion evolution. To represent the majority and expert impacts, we explicitly use the concept of opinion consistency and expertise level consistency respectively in an innovative way by capitalizing the notion of entropy in measuring the homogeneity of a group. Consequently, our model successfully captures the opinion dynamics under the concomitant influence of majority and expert. We validate the efficacy of our model in capturing opinion dynamics in a real world scenario using the opinion evolution traces collected from a widely used online social network (OSN) platform. Moreover, simulation results reveal the impact of the aforementioned effects, and confirm that our model can properly capture the consensus, polarization and fragmentation properties of public opinion. Our model is also compared with some recent models to evaluate its performance in both real world and simulated environments. © 2017, Springer Science+Business Media, LLC

An empirical testing of informational efficiency in Bangladesh capital market: Informational efficiency in Bangladesh capital market

We investigate how efficiently the stock market participants incorporate the information contained in money supply changes into stock prices in an emerging economy like Bangladesh. Of particular interest is to test how the changes inmonetary aggregates directly affect the stock prices through asset changes and indirectly through their effects on real economic activity. We have considered the monthly series of the real stock returns (P) and examine the relationship between stock returns and monetary aggregates from 1980 to 2008. We also include the exchange rate of US dollar against Bangladeshi Taka and industrial production index. The presence of cointegration between stock prices and monetary aggregates indicate long-run predictability of the Bangladesh stock market. The short-run dynamics between monetary aggregates and real stock return, relied on theoretically motivated long-run restrictions, are analyzed using an empirical structural VAR model. The dynamic response of the real stock returns to changes in macroeconomic variables (such as broad money supply, exchange rates), particularly its lagged responses to real economic activity generates inefficiency in the Dhaka Stock Exchange. The findings of this article indicate that informational inefficiency existsin the stock market of Bangladesh due to the presence of unidirectional causality. To be efficient, the infrastructure of the SEC should be modernized, revaluation of the net asset value of the companies should be audited by the affiliated firms of the SEC, demutualization should be done as early as possible, private placement, issue of preference share and book building methods must be under rule based. Insider trading should be strictly prohibited