Clinical and epidemiological aspects of human bocavirus infection

Human Bocavirus in Childhood: A True Respiratory Pathogen or a "Passenger" Virus? A Comprehensive Review

Recently, human bocavirus (HBoV) has appeared as an emerging pathogen, with an increasing number of cases reported worldwide. HBoV is mainly associated with upper and lower respiratory tract infections in adults and children. However, its role as a respiratory pathogen is still not fully understood. It has been reported both as a co-infectious agent (predominantly with respiratory syncytial virus, rhinovirus, parainfluenza viruses, and adenovirus), and as an isolated viral pathogen during respiratory tract infections. It has also been found in asymptomatic subjects. The authors review the available literature on the epidemiology of HBoV, the underlying risk factors associated with infection, the virus's transmission, and its pathogenicity as a single pathogen and in co-infections, as well as the current hypothesis about the host's immune response. An update on different HBoV detection methods is provided, including the use of quantitative single or multiplex molecular methods (screening panels) on nasopharyngeal swabs or respiratory secretions, tissue biopsies, serum tests, and metagenomic next-generations sequencing in serum and respiratory secretions. The clinical features of infection, mainly regarding the respiratory tract but also, though rarely, the gastrointestinal one, are extensively described. Furthermore, a specific focus is dedicated to severe HBoV infections requiring hospitalization, oxygen therapy, and/or intensive care in the pediatric age; rare fatal cases have also been reported. Data on tissue viral persistence, reactivation, and reinfection are evaluated. A comparison of the clinical characteristics of single infection and viral or bacterial co-infections with high or low HBoV rates is carried out to establish the real burden of HBoV disease in the pediatric population.

Impact of RSV Coinfection on Human Bocavirus in Children with Acute Respiratory Infections

OBJECTIVE

The objective of this study was to assess epidemiological and clinical features of human bocavirus (HBoV) coinfection with other viruses.

METHOD

Children coinfected with HBoV between January 2012 and December 2014 were enrolled and retrospectively reviewed.

RESULT

A total of 984 patients were stratified into five groups: HBoV infection alone (n = 249), respiratory syncytial virus (RSV) infection alone (n = 649), HBoV coinfection with RSV (n = 28), with human rhinovirus (HRV) (n = 39) and with other virus (n = 19). Length of hospitalization was longer in HBoV coinfection with RSV group than HBoV (9.0 days vs. 7.0 days, p = 0.001), RSV (9.0 days vs. 8.0 days, p = 0.016) infection alone group. Pneumonia was more common in the HBoV coinfection with RSV group compared with the HBoV, RSV infection alone group, respectively (75.0% vs. 44.2%, 31.3%, p < 0.001). HBoV DNA copy numbers (383 000 copies/ml) were positively correlated with the length of hospitalization (r = 0.334, p < 0.001).

CONCLUSION

HBoV coinfection with RSV increases HBoV infection severity.

Presence of rat bocavirus in oropharyngeal and fecal samples from murine rodents in China

In this study, we detected and genetically characterized rat bocavirus (RBoV) carried in 496 murine rodents that were captured in four provinces in China between May 2015 and May 2017. RBoV-positive samples were found in all four provinces, with a total positive rate of 24.8% (123/496) in throat swabs and 58.1% (286/492) in fecal samples. Twelve nearly full-length genome sequences of RBoV were determined, and the average sequence identity was 96.2%. Phylogenetic analysis showed that RBoVs formed a distinct clade that was distinguishable from the bocaviruses discovered in humans and other animals.

Detection of human bocaviruses 1, 2 and 3 in Irish children presenting with gastroenteritis

Human bocavirus has been increasingly detected worldwide in patients suffering from gastroenteritis, with the highest incidence reported in children aged between 6 and 24 months. A total of 155 non-bacterial gastroenteritis samples consisting of rotavirus-, adenovirus- and norovirus-positive specimens were collected from patients in the Munster region of Ireland from 2006-2008. Of these 155, a total of 12 were positive for the presence of human bocavirus. Three types of human bocavirus were identified: HBoV1, 2 and 3. In addition, recombinant strains (n=4) were also isolated. This is the first report of all three types of HBoV being detected in southern Ireland.

Parvoviruses: structure and infection

Parvoviruses package a ssDNA genome. Both nonpathogenic and pathogenic members exist, including those that cause fetal infections, encompassing the entire spectrum of virus phenotypes. Their small genomes and simple coding strategy has enabled functional annotation of many steps in the infectious life cycle. They assemble a multifunctional capsid responsible for cell recognition and the transport of the packaged genome to the nucleus for replication and progeny virus production. It is also the target of the host immune response. Understanding how the capsid structure relates to the function of parvoviruses provides a platform for recombinant engineering of viral gene delivery vectors for the treatment of clinical diseases, and is fundamental for dissecting the viral determinants of pathogenicity. This review focuses on our current understanding of parvovirus capsid structure and function with respect to the infectious life cycle.

High prevelance of human parvovirus infection in patients with malignant tumors

It is well known that the immunity of patients with malignant tumors decreases significantly. An increased parvovirus B19 (B19) infection rate has been observed in immunocompromised hosts. However, only a small amount of literature regarding the risk of human parvovirus infection in patients with malignant tumors is available. To evaluate the correlation of human parvovirus infection with malignant tumors, 288 serum samples from patients with malignant tumors were screened for B19 DNA by nested-PCR. The serum samples, 156 of which were from known clinicopathological cancer patients, were subjected to analysis of the seropositive rate of human bocavirus (HBoV), hepatitis B virus (HBV) and transfusion transmitted virus (TTV) by PCR. A total of 800 normal population sera and 941 aspirate samples from children with respiratory tract infections were used as controls for the detection of B19 and HBoV, respectively. Pairwise comparison between cancerous serum and control samples, and the correlation between parvovirus infection and clinicopathological variables, including gender and cancer type, were evaluated using the χ2 test, Fisher's exact test or the t-test. P<0.05 was considered to indicate a statistically significant difference. The overall prevalence of B19 DNA in cancer patients was 50.69% (146/288), which was significantly higher than that of the healthy controls with 4.5% (36/800) (χ2 test, P<0.0001). Similar results were obtained for HBoV with a 39.74% (62/156) prevalence in cancer patients. However, the infection prevalence of HBV and TTV in the cancer patients was 5.13 (8/156) and 6.41% (10/156), respectively (P<0.0001), which was much less than that of B19 and HBoV. These results revealed that a high risk of B19 and HBoV infection occurred in cancer patients, and a potential correlation exists between parvovirus infection and occurrence of malignant tumors.

Diagnosis, management and possibilities to prevent parvovirus B19 infection in pregnancy

Human parvovirus B19 (B19V) infection in pregnancy can cause severe fetal anemia and nonimmune hydrops fetalis, which may be associated with spontaneous abortion and fetal death. Approximately 30–40% of women of child-bearing age are not immune to B19V infection. The risk to fetal life is particularly high if maternal infection occurs during the first 20 weeks of gestation. In this article we intend to give an overview on the molecular biology, epidemiology and management of B19V infection during pregnancy. These data will be combined with an assessment of the clinical situation of the infected fetus and the possibilities for avoiding and/or preventing B19V infection in pregnant women. Currently B19V infection is the causative agent of one of the most frequently occurring infectious complications in pregnancy that endangers fetal life, and so the necessity to develop a preventive vaccine is discussed.

Co-circulation of genetically distinct human metapneumovirus and human bocavirus strains in young children with respiratory tract infections in Italy

The discovery of human Metapneumovirus (hMPV) and human Bocavirus (hBoV) identified the etiological causes of several cases of acute respiratory tract infections in children. This report describes the molecular epidemiology of hMPV and hBoV infections observed following viral surveillance of children hospitalized for acute respiratory tract infections in Milan, Italy. Pharyngeal swabs were collected from 240 children ≤3 years of age (130 males, 110 females; median age, 5.0 months; IQR, 2.0–12.5 months) and tested for respiratory viruses, including hMPV and hBoV, by molecular methods. hMPV‐RNA and hBoV‐DNA positive samples were characterized molecularly and a phylogenetical analysis was performed. PCR analysis identified 131/240 (54.6%) samples positive for at least one virus. The frequency of hMPV and hBoV infections was similar (8.3% and 12.1%, respectively). Both infections were associated with lower respiratory tract infections: hMPV was present as a single infectious agent in 7.2% of children with bronchiolitis, hBoV was associated with 18.5% of pediatric pneumonias and identified frequently as a single etiological agent. Genetically distinct hMPV and hBoV strains were identified in children examined with respiratory tract infections. Phylogenetic analysis showed an increased prevalence of hMPV genotype A (A2b sublineage) compared to genotype B (80% vs. 20%, respectively) and of the hBoV genotype St2 compared to genotype St1 (71.4% vs. 28.6%, respectively). Interestingly, a shift in hMPV infections resulting from A2 strains has been observed in recent years. In addition, the occurrence of recombination events between two hBoV strains with a breakpoint located in the VP1/VP2 region was identified. J. Med. Virol. 83:156–164, 2011. © 2010 Wiley‐Liss, Inc.

Prevalence of nucleic acid sequences specific for human parvoviruses, hepatitis A and hepatitis E viruses in coagulation factor concentrates

BACKGROUND AND OBJECTIVES

Due to their high resistance to inactivation procedures, nonenveloped viruses such as parvovirus B19, human bocavirus (HBoV), human parvovirus 4 (PARV4), hepatitis A (HAV) and hepatitis E virus (HEV) pose a particular threat to blood products. Virus transmission to patients treated with blood products presents an additional burden to disease. We determined the frequency and the amount of nucleic acid specific for nonenveloped viruses in recently manufactured preparations of commercial coagulation factor concentrates.

MATERIALS AND METHODS

At least three different batches of each of 13 different plasma-derived and recombinant coagulation factor products were tested for the presence and the amount of nucleic acid for parvovirus B19, HBoV, human parvovirus 4, hepatitis A virus and HEV by using quantitative polymerase chain reaction.

RESULTS

Whereas none of the recombinant products tested positive for any of these viruses, parvovirus B19 DNA with amounts ranging between 2×10(1) and 1.3×10(3) genome equivalents/ml was detected in five plasma-derived products. In addition to parvovirus B19 genotype 1, genotypes 2 and 3 were observed in two batches of a factor VIII/von-Willebrand factor product. In two products (one factor VIII concentrate and one activated prothrombin complex concentrate), a combination of both genotypes 1 and 2 of parvovirus B19 was detected.

CONCLUSION

The data show that nucleic acids from several relevant nonenveloped viruses are not found at detectable levels in coagulation factor concentrates. In some cases, parvovirus B19 DNA was detectable at low levels. Testing of the plasma pools for the full range of parvovirus genotypes is advocated for ensuring product safety.

Correlation between bocavirus infection and humoral response, and co-infection with other respiratory viruses in children with acute respiratory infection

BACKGROUND

Human bocavirus (HBoV), a recently discovered virus, is prevalent among children with respiratory tract infection throughout the world. Co-infection was frequently found in HBoV-positive patients. Thus, whether HBoV is responsible for the respiratory disease is still arguable.

OBJECTIVES

A comprehensive study was carried out to integrate clinical and virological prevalence in HBoV-positive outpatient children, and to determine genetic and serologic characteristics of HBoV in Shanghai, China.

STUDY DESIGN

Nasal/throat swabs and sera were obtained over a 2-year period from 817 children with respiratory tract infection to examine the presence of HBoV and its co-infection. The seroepidemiology of HBoV was studied by ELISA and Western blot against the capsid protein VP2-based fragment. Persistence of HBoV was also analyzed in 12 pairs of return-visit cases.

RESULTS

HBoV was identified in 96 samples (11.8%). The co-infection rate with other respiratory viruses was 51%. IgM was detected in 55.7% of HBoV RT-PCR-positive patients, and in 72.7% of those who had high viral genome load. In addition, persistent viral DNA positivity was detected in 10 of 12 HBoV-positive cases tested, an average of 14 days later, and one child was still HBoV-positive after 31 days.

CONCLUSION

HBoV was found frequently in children with respiratory tract symptoms associated with other respiratory viruses, and persisted in the respiratory tract and in serum and urine. The presence of IgM was significantly more prevalent in viremic patients and those diagnosed with high load of HBoV DNA in nasal/throat swabs.

Rapid molecular evolution of human bocavirus revealed by Bayesian coalescent inference

Human bocavirus (HBoV) is a linear single-stranded DNA virus belonging to the Parvoviridae family that has recently been isolated from the upper respiratory tract of children with acute respiratory infection. All of the strains observed so far segregate into two genotypes (1 and 2) with a low level of polymorphism. Given the recent description of the infection and the lack of epidemiological and molecular data, we estimated the virus's rates of molecular evolution and population dynamics. A dataset of forty-nine dated VP2 sequences, including also eight new isolates obtained from pharyngeal swabs of Italian patients with acute respiratory tract infections, was submitted to phylogenetic analysis. The model parameters, evolutionary rates and population dynamics were co-estimated using a Bayesian Markov Chain Monte Carlo approach, and site-specific positive and negative selection was also investigated. Recombination was investigated by seven different methods and one suspected recombinant strain was excluded from further analysis. The estimated mean evolutionary rate of HBoV was 8.6x10(-4)subs/site/year, and that of the 1st+2nd codon positions was more than 15 times less than that of the 3rd codon position. Viral population dynamics analysis revealed that the two known genotypes diverged recently (mean tMRCA: 24 years), and that the epidemic due to HBoV genotype 2 grew exponentially at a rate of 1.01year(-1). Selection analysis of the partial VP2 showed that 8.5% of sites were under significant negative pressure and the absence of positive selection. Our results show that, like other parvoviruses, HBoV is characterised by a rapid evolution. The low level of polymorphism is probably due to a relatively recent divergence between the circulating genotypes and strong purifying selection acting on viral antigens.

Human bocavirus and rhino-enteroviruses in childhood otitis media with effusion

Background

Viral respiratory infections play an important role in the pathogenesis of otitis media with effusion (OME) in children. The most common human rhinoviruses (HRVs) have been detected in middle ear effusions (MEE), but there is only limited data available about the closely related human enteroviruses (HEVs). The newly discovered human bocavirus (HBoV) has not, however, been identified in MEE of OME children.

Objectives

The aim of our study was to determine the presence of HBoV and HRV/HEV and the rate of coinfection in a set of MEE samples collected from OME children.

Study design

Seventy-five MEE samples from 54 children with no acute respiratory symptoms were studied with reverse transcription polymerase chain reaction (RT-PCR) for detection of HRV/HEV and quantitative PCR for detection of HBoV.

Results

Twenty-six (35%) of 75 MEE samples were positive for viral nucleic acid, 22 (29%) for HEV, 10 (13%) for HRV and 2 (3%) for HBoV. There was no statistically significant difference between mucoid and serous effusions in the rate of virus detection. Forty-three percent of bilateral cases showed a contra-lateral difference in viral finding.

Conclusions

Our results suggest that these common respiratory viruses can be associated with OME in children. Whether these viruses are causative etiologic factors of MEE persistence or merely remnants of previous infections is not known.

CD4+ T helper cell responses against human bocavirus viral protein 2 viruslike particles in healthy adults

Background. Human bocavirus (HBoV) was recently described as a new member of the Parvoviridae family, and its possible association with respiratory illness in infants has been discussed. To date, HBoV genomes have been detected worldwide in respiratory tract samples obtained from children with pulmonary diseases, whereas only limited data on virus-specific immunity are available, mainly because of the lack of recombinant viral antigens.

Methods. HBoV viruslike particles (VLPs) were produced in insect cells and characterized by electron microscopy and cesium chloride gradient centrifugation. HBoV viral protein 2 (VP2)-specific antibodies and CD4⁺ T helper cell responses were analyzed by enzyme-linked immunsorbent assay and enzyme-linked immunospot assay.

Results. VP2 capsid proteins of HBoV were produced in insect cells infected with a recombinant baculovirus, and the formation of icosahedral VLPs (diameter, 21–25 nm; sedimentation density, 1.33 g/cm³) was demonstrated. A significant increase in secretion of VP2-specific interferon-γ was detected in cultures of peripheral blood mononuclear cells obtained from 69 healthy adults found to be positive for HBoV-specific immunoglobulin G antibodies, compared with control stimulations. In parallel, T cell responses against identically expressed parvovirus B19 VP2 VLPs were frequently observed in the individuals studied, without there being obvious cross-reactions between HBoV and parvovirus B19.

Conclusions. Data suggest the presence of HBoV-specific immune responses in adults and strongly support a high prevalence of HBoV among humans.