Distribution patterns of BK polyomavirus (BKV) subtypes and subgroups in American, European and Asian populations suggest co-migration of BKV and the human race

BK polyomavirus (BKV) is ubiquitous in the human population, infecting children asymptomatically and then persisting in the kidney. Based on serological and genotyping methods, BKV isolates worldwide are classified into four subtypes (I-IV), with subtype I prevalent throughout the world, subtype IV prevalent in Asia and part of Europe, and subtypes II and III rare throughout the world. Phylogenetic analyses of complete genome sequences have identified several geographically distinct subgroups of subtypes I and IV. To explain how the geographical distribution patterns of BKV subtypes and subgroups were formed, this study hypothesized that BKV co-migrated with human populations (the co-migration hypothesis), and examined this hypothesis by comparing the BKV subtype and subgroup profiles among two American populations in North-east USA and southern California, two European populations in Finland and Ireland/England, and two Asian populations in Japan and China (both American populations were composed mainly of European Americans). The frequency of subtype I was always the highest throughout the populations, but that of subtype IV was variable among populations. A subgroup of subtype I (I/b-2) was detected primarily in all of the European and American populations, whereas subgroup I/c was predominant in the Asian populations (the observed difference was statistically significant). Additionally, all of the five fully sequenced subtype IV isolates from the American and European populations belonged to subgroup IV/c-2, whereas all subtype IV isolates from the Asian populations belonged to the other subgroups. Collectively, the current findings provide support for the co-migration hypothesis.