In the current study, we have examined primary B-HAE cultures obtained from three different donors. HBoV1 infection of primary B-HAE was persistent and caused morphological changes of the epithelia, i.e. disruption of the tight barrier junctions, loss of cilia and epithelial cell hypertrophy. The loss of the former, plasma membrane structures that seal the perimeters of the polarized epithelial cells of the monolayer, is known to damage the cell barrier necessary to maintain vectorial secretion, absorption and transport. ZO-1, which we monitored here, is specifically associated with the tight junctions and remains the standard marker for these structures. Similarly, cilia play important roles in airway epithelia, in that they drive inhaled particles that adhere to mucus secreted by goblet cells outward [63] . HBoV1 infection compromises barrier function, and thus potentially increases permeability of the airway epithelia to allergens and susceptibility to secondary infections by microbes. The observed shedding of virus from the basolateral surface of infected primary HAE, albeit at a lower level (,1 log lower than that from the apical surface), is consistent with the facts that HBoV1 infection disrupted the polarity of the pseudo-stratified epithelial barrier and resulted in the leakage to the basolateral chamber. This explanation is also supported by HBoV1 infection of CuFi-HAE, where disruption of the tight junction structure was less severe and virus was released only from the apical membrane. The induction of leakage by HBoV1 also suggests a mechanism that accounts for the viraemia observed in HBoV1-infected patients [5] . Further disease pathology could be accounted for by infection-induced loss of cilia of the airway epithelia; a lack of cilia is often responsible for bronchiolitis [64] [65] [66] . Therefore, our study provides direct evidence that HBoV1 is pathogenic to polarized HAE, which serves as in vitro model of the lung [57, 58] . Since HBoV1 is frequently detected with other respiratory viruses in infants hospitalized for acute wheezing [2, [10] [11] [12] , the apparent pathological changes observed in HBoV1-infected HAE suggest that prior-infection of HBoV1 likely facilitates the progression of co-infection-driven pathogenesis in the patient.