title: Rapid molecular evolution of human bocavirus revealed by Bayesian coalescent inference.
abstract: Human bocavirus (HBoV) is a linear single-stranded DNA virus belonging to the Parvoviridae family that has recently been isolated from the upper respiratory tract of children with acute respiratory infection. All of the strains observed so far segregate into two genotypes (1 and 2) with a low level of polymorphism. Given the recent description of the infection and the lack of epidemiological and molecular data, we estimated the virus's rates of molecular evolution and population dynamics. A dataset of forty-nine dated VP2 sequences, including also eight new isolates obtained from pharyngeal swabs of Italian patients with acute respiratory tract infections, was submitted to phylogenetic analysis. The model parameters, evolutionary rates and population dynamics were co-estimated using a Bayesian Markov Chain Monte Carlo approach, and site-specific positive and negative selection was also investigated. Recombination was investigated by seven different methods and one suspected recombinant strain was excluded from further analysis. The estimated mean evolutionary rate of HBoV was 8.6x10(-4)subs/site/year, and that of the 1st+2nd codon positions was more than 15 times less than that of the 3rd codon position. Viral population dynamics analysis revealed that the two known genotypes diverged recently (mean tMRCA: 24 years), and that the epidemic due to HBoV genotype 2 grew exponentially at a rate of 1.01year(-1). Selection analysis of the partial VP2 showed that 8.5% of sites were under significant negative pressure and the absence of positive selection. Our results show that, like other parvoviruses, HBoV is characterised by a rapid evolution. The low level of polymorphism is probably due to a relatively recent divergence between the circulating genotypes and strong purifying selection acting on viral antigens.
authors.affiliation: Università degli Studi di Milano, Dipartimento di Scienze Cliniche L. Sacco, Sezione di Malattie Infettive, Via G.B. Grassi, 74 - 20157 Milano, Italy. gianguglielmo.zehender@unimi.it <gianguglielmo.zehender@unimi.it>
authors.forename: Gianguglielmo
authors.initials: G
authors.lastname: Zehender
authors.forename: Chiara
authors.initials: C
authors.lastname: De Maddalena
authors.forename: Marta
authors.initials: M
authors.lastname: Canuti
authors.forename: Alessandra
authors.initials: A
authors.lastname: Zappa
authors.forename: Antonella
authors.initials: A
authors.lastname: Amendola
authors.forename: Alessia
authors.initials: A
authors.lastname: Lai
authors.forename: Massimo
authors.initials: M
authors.lastname: Galli
authors.forename: Elisabetta
authors.initials: E
authors.lastname: Tanzi
mesh_terms: D001499:Bayes Theorem; D052660:Bocavirus / Q000235:genetics*; D019143:Evolution, Molecular; D005260:Female; D006801:Humans; D007223:Infant; D008297:Male; D008390:Markov Chains; D009010:Monte Carlo Method; D010322:Parvoviridae Infections / Q000821:virology*; D010614:Pharynx / Q000821:virology; D010802:Phylogeny; D011995:Recombination, Genetic; D012141:Respiratory Tract Infections / Q000821:virology; D012641:Selection, Genetic