Human Bocavirus Infection, Canada

Human Bocavirus was detected in 18 (1.5%) of 1,209 respiratory specimens collected in 2003 and 2004 in Canada. The main symptoms of affected patients were cough (78%), fever (67%), and sore throat (44%). Nine patients were hospitalized; of these, 8 (89%) were <5 years of age.

A new parvovirus, human Bocavirus (HBoV), was recently identified in Sweden (1). The virus was identified in clinical specimens from infants and children with respiratory tract illness. Phylogenetic analyses of the complete genome of HBoV showed that that the virus is most closely related to canine minute virus and bovine parvovirus, which are members of the genus Bocavirus, family Parvoviridae (1). To date, the only parvovirus known to be pathogenic in humans is B19, which is responsible for Fifth disease in children (2). The role of HBoV in respiratory tract illnesses is unknown. We retrospectively investigated HBoV in Canadian patients with acute respiratory infection (ARI) in 2003 and 2004 to assess the impact of HBoV infections on respiratory tract illnesses and identify the signs and symptoms of this illness.

The Study
A total of 1,209 specimens from patients with ARI from January 2003 to December 2004 were tested for HBoV. The specimens originated from the Saskatchewan provincial public health laboratories. Specimen types analyzed included throat swabs, nasopharyngeal swabs, nasopharyngeal aspirates, and auger suctions. All specimens were negative for influenza viruses A and B; parainfluenza viruses 1, 2, and 3; adenovirus; and respiratory syncytial virus (RSV) by direct or indirect fluorescence assays or virus isolation and for human metapneumovirus (HMPV) by reverse transcription-polymerase chain reaction. Specimens were collected from all age groups: 290 (24%) from those <5 years of age, 59 (5%) from those 6-10 years of age, 90 (7.4%) from those 11-15 years of age, 86 (7.1%) from those 16-20 years of age, 358 (29.6%) from those 21-50 years of age, and 324 (27%) from those >50 years of age, The age of the patients was unknown for 2 (0.2%) specimens.
A total of 18 (1.5%) of the 1,209 specimens tested were positive for HBoV by PCR. HBoV activity was found throughout the year with no apparent seasonal prevalence ( Table 1). The sex distribution of patients was 61% (11) male and 39% (7) female (Table 2). Patients with HBoV ranged in age from 10 months to 60 years (median 11.5 years), and no significant difference in infection rates was observed between age groups.

Conclusions
Although a causal relationship still needs to be demonstrated by including a control group of healthy persons, detection of HBoV in respiratory tract specimens from patients with undiagnosed ARI suggests that this virus may be associated with respiratory illness. This finding supports those of Allander et al. with regard to the association of HBoV with respiratory disease (1). It also demonstrates that HBoV was present in Canada in 2003 and 2004, which suggests that it may be circulating worldwide. Since this study used only samples from ARI patients who tested negative for influenza viruses A and B, parainfluenza viruses 1-3, adenovirus, RSV, and HMPV, dual infection cannot be excluded. In addition, whether HBoV is present asymptomatically in humans cannot be excluded because samples from healthy persons were not tested.
Allander et al. reported HBoV only in infants and children, which was probably the result of testing fewer specimens from adults patients (1). Most respiratory viruses show a seasonal distribution with peak activity in winter. Human parvovirus B19, the only parvovirus that is pathogenic in humans, is also seasonal, with peak occurrences in spring and summer (3). In contrast, no seasonal prevalence was observed for HBoV infection; the virus was found throughout the year. The lack of seasonality observed for HBoV may have been caused by the low prevalence in this study. Thus, additional year-round studies are needed to better understand the epidemiology of HBoV. Most (89%) hospitalizations were in persons <5 years of age, which suggests that HBoV may cause more severe respiratory illness in infants and children, similar to disease caused by RSV (4,5), HMPV (6,7), human coronavirus NL63 (8)(9)(10)(11)(12)(13)(14), and human coronavirus 229E (15). More comprehensive studies with data on prevalence, risk factors, and use of health services are needed to determine the role of HBoV in ARI and its effect on the healthcare system. This study was supported by the Public Health Agency of Canada.
Dr Bastien is a scientist at the National Microbiology Laboratory of the Public Health Agency of Canada in Winnipeg. Her research interests include the diagnosis and pathogenesis of respiratory viruses.