Seroepidemiology of human bocaviruses 1-4 - PubMed (original) (raw)

Seroepidemiology of human bocaviruses 1-4

Kalle Kantola et al. J Infect Dis. 2011 Nov.

Abstract

Background: Recently, 3 new members of the genus Bocavirus, human bocavirus 2 (HBoV2), human bocavirus 3 (HBoV3), and human bocavirus 4 (HBoV4), were discovered. HBoV2-4 occur mainly in the gastrointestinal tract but rarely in the respiratory tract, contrary to human bocavirus 1 (HBoV1).

Methods: To investigate HBoV1-4 seroepidemiology among 195 adults and 252 wheezing children, we conducted immunoglobulin G (IgG) and immunoglobulin M (IgM) enzyme immunoassays with recombinant viruslike particles (VLPs). The children's sera were also tested for HBoV1-4 DNA by quantitative polymerase chain reaction (qPCR).

Results: Both rabbit and human antibodies to HBoV1-4 VP2 VLPs were found to be cross-reactive. After depletion of HBoV1-reactive antibodies, the HBoV2-4 approximate seroprevalences in adults were 34%, 15%, and 2% and in children aged 1-2 years 25%, 10%, and 5%, respectively. After depletion of HBoV2-4-reactive antibodies, the HBoV1 seroprevalence among adults decreased from 96% to 59%. No cross-reactivity of human anti-HBoV IgG was observed with bovine parvovirus1, parvovirus B19 or PARV4. No child was HBoV2-4 viremic.

Conclusions: HBoV2-4 infect humans less commonly and elicit weaker B-cell responses than HBoV1. In our study HBoV2-4 did not seem to have a major etiological role in wheezing. Cross-reactivity with HBoV2-4 IgG partially accounts for the high HBoV1 seroprevalences previously reported. Correction for cross-reactivity is a prerequisite for VLP-based HBoV seroepidemiology.

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Figures

Figure 1.

Figure 1.

Determination of inflection points for human bocavirus 1 (HBoV1) and human bocavirus 2 (HBoV2) enzyme immunoassays. For the HBoV1 assay, the samples were not competed (A) or competed (B) with HBoV2–4 viruslike particles (VLPs). Similarly, for the HBoV2 assay, the samples were not competed (C) or competed (D) with HBoV1 VLPs. A linear regression curve has been fitted to the left, linear part of the curve. The deviation point of the linear regression line from the curve approximates the inflection point. R2 = square of the correlation coefficient.

Figure 2.

Figure 2.

Immunoglobulin G (IgG) seroreactivity (mean ± range) with human bocavirus (HBoV) virus protein 2 (VP2) viruslike particles (VLPs) after competition with various concentrations (x axes) of soluble heterologous HBoV VLPs indicated in the captions. Sera from 3 children and 4 adults positive for HBoV1, HBoV2, or HBoV3 were selected based on the apparent presence of IgG for only 1 HBoV species indicated in the leftmost vertical boxes. The boxes also indicate the type of VLP used for IgG detection. The HBoV4-IgG-positive adult serum also showed IgG for HBoV1, whereas no suitable HBoV4 IgG-positive child serum was available for the assays. Merkel cell polyomavirus (MCPyV) VLPs were used for control of nonspecific competition.

Figure 3.

Figure 3.

Reactivities of human bocavirus 1 (HBoV1) and human bocavirus 2 (HBoV2) rabbit antisera with human parvovirus and bovine parvovirus (BPV) viruslike particles (VLPs). The sera were studied in serial dilutions indicated on the x axis. Merkel cell polyomavirus (MCPyV) VLPs were used as a negative control to account for unspecific binding.

Figure 4.

Figure 4.

Immunoglobulin G (IgG) (A) and immunoglobulin M (IgM) (B) reactivities of 21 wheezing children's paired sera with human bocavirus 1 (HBoV1), human bocavirus 2 (HBoV2), human bocavirus 3 (HBoV3), and human bocavirus 4 (HBoV4) viruslike particles (VLPs). The sera were selected based on IgG seroconversion to HBoV1 VLPs, and most showed multiple markers of acute HBoV1 infection [21]. For IgG results, I = acute-phase (at the time of admission) serum without competition; II = convalescent-phase (2 weeks later) serum without competition; II/B = convalescent-phase serum competed with soluble HBoV2–4 viruslike particles (VLPs). IgM results are shown without separation between acute-phase and convalescent-phase samples. The previously established cutoff (0.167) for HBoV1 IgM detection [21] is shown for reference.

Figure 5.

Figure 5.

Immunoglobulin G (IgG) reactivity of 115 sera from Finnish medical students with viruslike particles (VLPs) from human bocaviruses (HBoVs) 1–4 (indicated on the x axis). The sera were not competed (A), competed with HBoV1 VLPs (B), or competed with a mixture of HBoV2–4 VLPs (C) prior to the assays. The sera were tested for residual reactivity after homologous competition with HBoV1 VLPs (B); HBoV1 reactivity) or with a mixture of HBoV2–4 VLPs (C); combined HBoV2, HBoV3, and HBoV4 reactivity). The lowest IgG cutoff of 0.11 (HBoV2–4, competed) is shown for reference. In routine testing, we calculated the net reactivity as the raw optical density (OD) subtracted with the corresponding residual OD from homologous competition. Residual reactivity for HBoV2–4 was tested with a pool of these antigens (60 ng each/well), whereas all other tests were done with individual antigens (60 ng/well).

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