Human BK and JC polyomaviruses: Molecular insights and prevalence in Asia

Polyomaviridae family consists of small circular dsDNA viruses. Out of the 14 human polyomaviruses described so far, BKPyV and JCPyV have been studied extensively since their discovery in 1971. Reportedly, both BKPyV and JCPyV are widely distributed across the globe with the frequency of 80-90 % in different populations. The primary infection of these viruses is usually asymptomatic and latent which is activated as a consequence of immunosuppression. Activated BKPyV and JCPyV viruses lead to the development of BK Virus Associated Nephropathy and Progressive Multifocal Leukoencephalopathy, respectively. Immense progress has been made during the last few decades regarding the molecular understanding of polyomaviruses. Epidemiology of polyomaviruses has also been studied extensively. However, most of the epidemiological studies have focused on European and American populations. Therefore, limited data is available regarding the geographical distribution of these potentially oncogenic viruses in Asian countries. In this article, we have presented a compendium of latest advances in the molecular understanding of polyomaviruses and their pathobiology. We also present a comprehensive review of published literature regarding the epidemiology and prevalence of BKPyV and JCPyV in Asian regions. For this purpose, a thorough search of available online resources was performed. As a result, we retrieved 24 studies for BKPyV and 22 studies for JCPyV, that describe their prevalence in Asia. These studies unanimously report high occurrence of both BKPyV and JCPyV in Asian populations. The available data from these studies was categorized into two groups: on the basis of prevalence (low, medium and high) and disease development (healthy and diseased). Altogether, Korean population hasbeen evidenced to possess highest frequency of BKPyV (66.7 %), while JCPyV was found to be most prevalent in Taiwan (88 %). Due to high and ubiquitous distribution of these viruses, frequent studies are required to develop a better understanding regarding the epidemiology and pathobiology of these viruses in Asia.

Evolution and molecular epidemiology of polyomaviruses

Polyomaviruses (PyVs) are small DNA viruses that infect several species, including mammals, birds and fishes. Their study gained momentum after the report of previously unidentified viral species in the past decade, and especially, since the description of the first polyomavirus clearly oncogenic for humans. The aim of this work was to review the most relevant aspects of the evolution and molecular epidemiology of polyomaviruses, allowing to reveal general evolutionary patterns and to identify some unaddressed issues and future challenges. The main points analysed included: 1) the species and genera assignation criteria; 2) the hypotheses, mechanisms and timescale of the ancient and recent evolutionary history of polyomaviruses; and 3) the molecular epidemiology of human viruses, with special attention to JC, BK and Merkel cell polyomaviruses.

Utility of JC polyomavirus in tracing the pattern of human migrations dating to prehistoric times

JC virus (JCV) is a double-stranded DNA polyomavirus co-evolving with humans since the time of their origin in Africa. JCV seems to provide new insights into the history of human populations, as it suggests an expansion of humans from Africa via two distinct migrations, each carrying a different lineage of the virus. A possible alternative to this interpretation could be that the divergence between the two lineages is due to selective pressures favouring adaptation of JCV to different climates, thus making any inference about human history debatable. In the present study, the evolution of JCV was investigated by applying correspondence analysis to a set of 273 fully sequenced strains. The first and more important axis of ordination led to the detection of 61 nt positions as the main determinants of the divergence between the two virus lineages. One lineage includes strains of types 1 and 4, the other strains of types 2, 3, 7 and 8. The distinctiveness of the Caucasian lineage (types 1 and 4), largely diffused in the northern areas of the world, was almost entirely ascribed to synonymous substitutions. The findings provided by the subsequent axes of ordination supported the view of an evolutionary history of JCV characterized by genetic drift and migration, rather than by natural selection. Correspondence analysis was also applied to a set of 156 human mitochondrial genome sequences. A detailed comparison between the substitution patterns in JCV and mitochondria brought to light some relevant advantages of the use of the virus in tracing human migrations.