Human bocavirus infection in children with acute gastroenteritis in Japan and Thailand

INTRODUCTION

Acute gastroenteritis is one of the most common diseases in infant and children and continues to be a significant cause of morbidity and mortality worldwide [Musher and Musher, 2004]. Rotavirus, calicivirus, astrovirus, and adenovirus have been established as the most important etiologic agents [Glass et al., 2001; Marie-Cardine et al., 2002]. However, the etiologic agents of more than a half of patients with acute gastroenteritis are undiagnosed [Simpson et al., 2003; Olesen et al., 2005; Chanit et al., 2009]. In 2005, human bocavirus (HBoV) was first identified in pooled human respiratory tract specimens from Swedish children with respiratory tract disease and classified into the genus Bocavirus of the subfamily Parvovirinae, family Parvoviridae [Allander et al., 2005]. The HBoV genome is approximately 5.2 kb nucleotides in length and contains three open-reading frames (ORF) encoding two non-structural proteins (NS1 and NP-1) and two capsid proteins (VP1 and VP2). Subsequently, the virus has been detected in children with respiratory tract infection in the world including Europe, Asia, Africa, America, and Australia. Among these studies, the prevalence of HBoV infection has been described to vary considerably between 1.5% and 19% [Kesebir et al., 2006; Ma et al., 2006; Sloots et al., 2006; Smuts and Hardie, 2006; Allander et al., 2007; Bastien et al., 2007; Chieochansin et al., 2007; Allander, 2008; Calvo et al., 2008; Jacques et al., 2008; Smuts et al., 2008; Zeng et al., 2010; Zheng et al., 2010]. Recently, HBoV has been detected in 0.5–9.1% of fecal specimens obtained from children with acute gastroenteritis in Spain, Germany, Hong Kong, Korea, China, Japan, and Brazil [Albuquerque et al., 2007; Lau et al., 2007; Lee et al., 2007; Vicente et al., 2007; Nakanishi et al., 2009].

The present study aimed to screen stool samples collected from Japanese and Thai children with acute gastroenteritis during 2005–2008 for HBoV infection, one of less explored viral pathogens which has been reported to be associated with diarrhea recently, and to characterize the detected HBoV strains.

MATERIALS AND METHODS

RESULTS

Of the 329 samples tested, 6 (1.8%) were positive for HBoV. Of these, five samples were collected from Japan and one sample was from Thailand. As a result, the detection rates of HBoV in each country were 2% and 1.2%, respectively. For the five Japanese HBoV-positive samples, three were collected in Maizuru and the two remaining were from Osaka.

For clinical characterization, only data from five Japanese patients were available for analysis. All five Japanese children whose stool specimens showed positive for HBoV were infants aged from 8 to 19 months. All positive samples were detected in either April or May. Diarrhea in these patients lasted from 3 to 6 days, and the number of diarrheal episodes per day was <10. None of the patients was noted with fever, vomiting, dehydration, or respiratory symptoms. Co-detections of HBoV and HPeV or Aichi virus were not found (Table I).

All positive PCR products of the NP-1 gene were confirmed by sequencing (GenBank). The virus detected in these patients was defined as HBoV by phylogenetic analysis (Fig. 1A). For the classification of the detected viruses, Figure 1B showed that: four Japanese studied HBoV strains were clustered into group 1, while the remaining Japanese strain and a unique Thai strain belonged to group 2.

DISCUSSION

In this study, detection rates of HBoV in the samples tested from Japan and Thailand were found to be 2% and 1.2%, respectively. However, they do not represent the percentages of cases of infection with HBoV in all patients with acute gastroenteritis during 1-year period, because only samples which had been known to be negative for rotavirus, adenovirus, norovirus, sapovirus, and astrovirus were screened for HBoV. As a result, possible mixed infection of enteric viruses was excluded from analysis.

To date, HBoV has been detected in samples from respiratory tract and has been associated with both upper and lower respiratory tract diseases in infants and children [Kesebir et al., 2006; Ma et al., 2006; Sloots et al., 2006; Smuts and Hardie, 2006; Allander et al., 2007; Bastien et al., 2007; Chieochansin et al., 2007; Allander, 2008; Calvo et al., 2008; Jacques et al., 2008; Smuts et al., 2008; Zeng et al., 2010; Zheng et al., 2010]. HBoV was also present in gastrointestinal tract in children with gastroenteritis [Albuquerque et al., 2007; Lau et al., 2007; Lee et al., 2007; Vicente et al., 2007; Nakanishi et al., 2009]. However, its role in patients with acute gastroenteritis is unclear. In this study, HBoV was detected in stool samples collected from infants with acute gastroenteritis without symptoms of respiratory infection. In addition, the absence of any other intestinal pathogens such as rotavirus, adenovirus, norovirus, sapovirus, astrovirus, human parechovirus, and Aichi virus suggests that this virus is an enteric pathogen, a possible causative agent of diarrhea in the studied patients.

In Japan, the detection of HBoV in rectal swabs from children with acute gastroenteritis was reported once in Sapporo in northern Japan [Nakanishi et al., 2009]. In that study, four samples were positive for HBoV by RT-PCR with the detection rate of 0.5%; however, HBoV genotyping was not done in the four samples. In the present study, the virus was found in infants and children with acute gastroenteritis in Maizuru and Osaka located in southern Japan. In Thailand, HBoV detection in children with acute gastroenteritis was first reported in Bangkok (HBoV group 3, detection rate of 0.9%) [Chieochansin et al., 2008]. Taken together with the previous studies, the findings suggest that this virus may be a possible and infrequent causative agent of Japanese and Thai infants and children with acute gastroenteritis.

To our knowledge, this is the first report of the circulating of HBoV groups 1 and 2, and of HBoV group 2 in infants and children with acute gastroenteritis in Japan and Thailand, respectively. The findings provide better understanding on the epidemiological characteristics of HBoV infections in Japan and Thailand and contribute useful data for future research into HBoVs.