Seroepidemiology of human bocavirus in Apulia, Italy

RESEARCH NOTE

Seroepidemiology of human bocavirus in Apulia, Italy M. Guido1,*, A. Zizza2,*, S. Bredl3, J. Lindner3, A. De Donno1, M. Quattrocchi1, P. Grima4, S. Modrow3 and the Seroepidemiology Group  1) Laboratory of Hygiene, Department of Biological and Environmental Sciences and Technologies, Faculty of Sciences, University of Salento, Lecce, 2) Institute of Clinical Physiology, National Research Council, Lecce, Italy 3) Institute of Medical Microbiology and Hygiene, University of Regensburg, Regensburg, Germany and 4) Division of Infectious Diseases, S. Caterina Novella Hospital, Galatina, Lecce, Italy

Abstract A serological survey was performed to determine the prevalence of antibodies against human bocavirus in an Apulian population. Anti-hBoV IgG antibodies were analysed in 1206 inhabitants (age range, 1 month–84 years) using a standardized ELISA test based on the use of recombinant hBoV VP2 virus-like particles. In total, 1075 (89.1%) of 1206 participants (mean age 32 ± 24.8 years) displayed anti-hBoV-IgG. The seroprevalence increased significantly (p < 0.0001) in children from 2–4 years (64.2%) to 5–9 years (96.4%). A similar trend was observed in both male and female subjects. In conclusion, our results show that hBoV infection is common in this population, especially in children.

Keywords: Human bocavirus, IgG antibody, seroprevalence, virus-like particles Original Submission: 9 November 2011; Revised Submission: 16 December 2011; Accepted: 16 December 2011 Editor: L. Kaiser Article published online: 26 December 2011 Clin Microbiol Infect 2012; 18: E74–E76 10.1111/j.1469-0691.2011.03756.x

Corresponding author: Marcello Guido, Laboratory of Hygiene, Department of Biological and Environmental Sciences and Technologies, University of Salento, Via Prov. le Lecce-Monteroni, 73100 Lecce, Italy E-mail: [email protected] *These authors contributed equally to this work.   Seroepidemiology Group: Basile R, Bruno A, Campilongo F, Cotrino G, De Benedittis MG, Pensa P, Romano C, Tinelli A.

VIROLOGY

Human bocavirus (hBoV) is a newly identified human parvovirus associated with respiratory tract infections [1]. Until now four genetic subgroups of hBoV were known to infect humans (hBoV1–4) [1–4]. HBoV1 has been shown to be prevalent in upper and lower respiratory tract infections, frequently in association with other viruses, but has been also detected in serum, urine and faecal samples [5–11]. HBoV1 isolates show a low degree of genetic variability [4]. HBoV2– 4 isolates share between 67 and 80% of nucleotide sequences with hBoV1 [2,3]. They have been mainly detected in patients with infection of the gastrointestinal tract, and rarely in those with infection of the respiratory tract [12]. Most of the epidemiological and clinical studies have been conducted on children and hospitalized paediatric patients with respiratory infections. Therefore the results may not reflect the real seroprevalence of hBoV in the general population [13]. Moreover, the high presence of co-infections with other respiratory viruses may complicate the analysis of clinical, virological and serological aspects in hBoV infection [8,14]. Only a few studies have been conducted to evaluate the seroprevalence of hBoV in the general population that are not representative of the virus spread in all age groups [5– 16]. We performed a regional cross-sectional populationbased study to estimate the prevalence of hBoV-specific IgG in Apulia, south Italy. Serum specimens were collected from healthy subjects, who were not hospitalized, and frozen at )80C until use. In particular, the serum samples were residual sera from subjects who applied for a health check. Age, gender and date of sampling were reported for each case. Local ethics committees approved this study and informed consent was obtained. Immunocompromised patients, recipients of blood transfusion during the previous 6 months and individuals suffering from acute infectious disease were excluded from the study. A total of 1206 samples were collected from June 2009 to May 2010 (0–5 months, n = 38; 6–11 months, n = 35; 1 year, n = 67; 2–4 years, n = 81; 5–9 years, n = 139; 10–14 years, n = 89; 15–19 years, n = 112; 20–29 years, n = 105; 30– 39 years, n = 106; 40–49 years, n = 104; 50–59 years, n = 105; 60–69 years, n = 112; ‡70 years, n = 113). All samples had to be equally representative of male and female subjects. IgG-antibodies against hBoV VP2-proteins were quantified using a standardized ELISA based on VP2 virus-like particles (VLP) as antigen [15]. Assuming an overall hBoV prevalence of 85%, 1200 samples were required to achieve 95% confidence level, with a precision of the estimate of 7% and with a study power of 80.0%. The statistical analysis was performed using STATVIEW5.1 (STATVIEW, Berkeley, CA, USA). Differences between percentages have been assessed using the chi-

ª2011 University of Salento Clinical Microbiology and Infection ª2011 European Society of Clinical Microbiology and Infectious Diseases

Research Note

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squared test and Fisher’s exact test as needed. Comparison between geometric mean titres (GMT) was assessed by twotailed unpaired Student’s t-test. A p value <0.05 was considered statistically significant. One thousand and seventy-five out of 1206 analysed samples (89.1%; age range, 1 month to 84 years) were tested positive for hBoV-specific IgG, 126 (10.4%) negative and 5 (0.4%) equivocal. Anti-hBoV-IgG was detected in 73.7% of infants aged 0–5 months and in 51.4% (p < 0.05) of the age group 6–11 months. The seropositive rate increased significantly between the age groups of 2–4 years (64.2%) and 5– 9 years (96.4%; p < 0.0001). Similar trends were observed by testing the respective age groups of male subjects (65.8% vs. 95.6%; p < 0.0001) and female subjects (62.8% vs. 97.2%; p < 0.0001) (Fig. 1). In children aged >2–4 years seroprevalence increased to more than 90%. Geometric Mean Titre (GMT) value ranged from 1052.6 ± 61.7 Relative Units (RU) (0–5 months) to 912.2 ± 271.5 RU (age ‡70 years), with a peak of 1398.5 ± 278.3 RU in those aged 1 year. A significant decrease (p < 0.05) was observed for GMT in girls at the age of 1 year vs. 2–4 years (1684.6 ± 168.2 RU/mL vs. 1010.2 ± 203.4 RU/mL) and among those aged 20–29 vs. 30– 39 years (1245.1 ± 442.7 RU/mL vs. 741.2 ± 218.1 RU/mL) (Fig. 2). This is the first report that evaluates the seroepidemiology of hBoV1 infection in Italy. In this study we examined the prevalence of hBoV-specific IgG antibodies in serum samples from individuals up to an age of more than 70 years. Our data indicate hBoV infection to be ubiquitous in the general population and to be acquired early in preschool children. More than 90% of subjects older than 4 years displayed previous exposure to hBoV. The high se-

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roprevalence that was observed in newborns and in children during the first months of life is assumed to be related to maternal antibodies; decreasing values were observed in the group of children aged 6–11 months. The results showed that primary hBoV infection occurs between 6 and 48 months, as previously described [14]. Our data show a similar trend to that observed in the few serological studies [8,13,16,17]. However, the overall seroprevalence (89.1%) is higher than that observed by Zhao et al. (59.1%) [16] and Endo et al. (71.1%) [17]. This could be due to testing a sample size that may be more representative of the general population or to geographical variations in hBoV epidemiology. A recent study showed both intergenotypical and intragenotypical recombinants to occur between hBoV1 and hBoV4 and between hBoV2 variants, respectively [12]. About 80% of genomic organization of VP1 and VP2 antigens is identical [3] but the VP2 antigen seems to be the most conserved and immunogenic protein [18]. The high hBoV1 IgG prevalence could be due to cross-reactivities among VP2 antigens of hBoV1 and hBoV2-4 [12], thereby resulting in an overestimation of hBoV1 circulation. This interpretation could explain the high isolation rate of hBoV1 found in adult patients with influenza-like illness (ILI) [19]. It remains to be clarified whether antibodies produced against a specific hBoV genotype may also neutralize related variants of hBoV. Such cross-immunity might have clinical relevance in the management of respiratory and gastrointestinal hBoVcorrelated infections. The presence and the high hBoV load in respiratory tract infections, frequently associated with other viruses, implies an important role in the pathogenesis of respiratory diseases

100

1800

70 60

Total

**

80

1600 1400

*

50

Total

40

Males

30

Females

20

GMT (R.U./ml)

Seroprevalence (%)

90

Males

*

Females

1200 1000

*

800 600

10

400

0

200 0

Age group (years)

FIG. 1. Human bocavirus seroprevalence by age group and gender

Age group (years)

in Apulia, 2009–2010. Statistical analysis was performed by Fisher’s

FIG. 2. Geometric mean titre (RU/mL) stratified by gender and age

exact test and/or the v2 test: *p < 0.05 between total groups of 0–5

group in Apulia, 2009–2010. Values are given as mean ± standard

months and 6–11 months; **p < 0.0001 between total groups of 2–4

deviation. Statistical analysis was performed by unpaired t-test:

years and 5–9 years, male subjects of 2–4 years and 5–9 years, and

*p < 0.05 between female subjects of 1 year and 2–4 years, and

female subjects of 2–4 years and 5–9 years.

between female groups of 20–29 years and 30–39 years.

ª2011 University of Salento Clinical Microbiology and Infection ª2011 European Society of Clinical Microbiology and Infectious Diseases, CMI, 18, E74–E76

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[20], but the real pathogenic significance of the virus needs to be further elucidated. In conclusion, our results show the frequent circulation of hBoV in the general population. Further studies are needed to determine the exact clinical and epidemiological role of hBoV.

Authors’ Contributions GM, ZA and MS conceived the study and participated in its design and coordination and helped draft the manuscript. BS, LJ, DDA, QM and GP acquired and analyzed data and were involved in revising the manuscript critically for intellectual content. All the authors read and approved the final manuscript.

Acknowledgements The study is supported by the Ministry of Education, University and Research (MIUR), Project of Relevant National Interest (PRIN) 2007: Prevalence and molecular characterization of ‘new respiratory viruses (human metapneumovirus and human bocavirus) in Apulia’, no. 2007LPAF42_004 in the framework of ‘Respiratory infections: molecular epidemiology, cross-protection and impact of the preventive strategies’ project.

Transparency Declaration All the authors declare no conflicts of interest.

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