Abstract
BackgroundVaricella (chickenpox) exhibits a characteristic epidemiological pattern which is associated with climate. In general, primary infections in tropical regions are comparatively less frequent among children than in temperate regions. This peculiarity regarding varicella-zoster virus (VZV) infection among certain age groups in tropical regions results in increased susceptibility during adulthood in these regions. Moreover, this disease shows a cyclic behavior in which the number of cases increases significantly during winter and spring. This observation further supports the participation of environmental factors in global epidemiology of chickenpox. However, the underlying mechanisms responsible for this distinctive disease behavior are not understood completely. In a recent publication, Philip S. Rice has put forward an interesting hypothesis suggesting that ultra-violet (UV) radiation is the major environmental factor driving the molecular evolution of VZV.DiscussionWhile we welcomed the attempt to explain the mechanisms controlling VZV transmission and distribution, we argue that Rice's hypothesis takes lightly the circulation of the so called "temperate VZV genotypes" in tropical regions and, to certain degree, overlooks the predominance of such lineages in certain non-temperate areas. Here, we further discuss and present new information about the overwhelming dominance of temperate VZV genotypes in Mexico regardless of geographical location and climate.SummaryUV radiation does not satisfactorily explain the distribution of VZV genotypes in different tropical and temperate regions of Mexico. Additionally, the cyclic behavior of varicella does not shown significant differences between regions with different climates in the country. More studies should be conducted to identify the factors directly involved in viral spreading. A better understanding of the modes of transmissions exploited by VZV and their effect on viral fitness is likely to facilitate the implementation of preventive measures for disease control.
Highlights
Varicella exhibits a characteristic epidemiological pattern which is associated with climate
A better understanding of the modes of transmissions exploited by varicella-zoster virus (VZV) and their effect on viral fitness is likely to facilitate the implementation of preventive measures for disease control
Contrary to the characteristic epidemiology of temperate regions, where varicellazoster virus (VZV) infection is acquired early in life, in tropical regions infections among children are comparatively less common and disease is more frequent in adolescents and young adults [1,2]
Summary
The major weakness of Rice’s hypothesis is neglecting the predominance of the temperate genotypes in tropical regions. If UV radiation was to be the major force driving VZV genotype distribution, one might expect to see a radical change in the molecular epidemiology of those regions with tropical climates. No differences in the profiles were seen, apart from the total number of cases which are higher in tropical locations This is explained since in Mexico, in general terms, more individuals live in tropical regions than in temperate areas. We believe that Rice’s hypothesis is highly biased by the results published in one large study describing the global molecular epidemiology of varicella in twenty seven different countries [13]. Larger studies including representative numbers of specimens collected from tropical, subtropical and temperate regions are required to fully understand the global molecular epidemiology of VZV. With these new clear guidelines regarding VZV classification and the arrival of new sequencing technologies, a wealth of information is expected to be generated in the very near future
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