Recombination dynamics of human parechoviruses: investigation of type-specific differences in frequency and epidemiological correlates

Human parechoviruses (HPeVs) are highly prevalent RNA viruses classified in the family Picornaviridae. Several antigenically distinct types circulate in human populations worldwide, whilst recombination additionally contributes to the genetic heterogeneity of the virus. To investigate factors influencing the likelihood of recombination and to compare its dynamics among types, 154 variants collected from four widely geographically separated referral centres (UK, The Netherlands, Thailand and Brazil) were typed by VP3/VP1 amplification/sequencing with recombination groups assigned by analysis of 3Dpol sequences. HPeV1B and HPeV3 were the most frequently detected types in each referral region, but with marked geographical differences in the frequencies of different recombinant forms (RFs) of types 1B, 5 and 6. HPeV1B showed more frequent recombination than HPeV3, in terms both of evolutionary divergence and of temporal/geographical indicators of population separation. HPeV1 variants showing between 10 and 20% divergence in VP3/VP1 almost invariably fell into different recombination groups, compared with only one-third of similarly divergent HPeV3 variants. Substitution rates calculated by beast in the VP3/VP1 region of HPeV1 and HPeV3 allowed half-lives of the RFs of 4 and 20 years, respectively, to be calculated, estimates fitting closely with their observed lifespans based on population sampling. The variability in recombination dynamics between HPeV1B and HPeV3 offers an intriguing link with their markedly different seasonal patterns of transmission, age distributions of infection and clinical outcomes. Future investigation of the epidemiological and biological opportunities and constraints on intertypic recombination will provide more information about its influence on the longer term evolution and pathogenicity of parechoviruses.

Specific association of human parechovirus type 3 with sepsis and fever in young infants, as identified by direct typing of cerebrospinal fluid samples

BACKGROUND

Human parechoviruses (HPeVs), along with human enteroviruses (HEVs), are associated with neonatal sepsis and meningitis. We determined the relative importance of these viruses and the specific HPeV types involved in the development of central nervous system-associated disease.

METHODS

A total of 1575 cerebrospinal fluid (CSF) samples obtained during 2006-2008 were screened for HPeV by means of nested polymerase chain reaction. All samples for which results were positive were typed by sequencing of viral protein (VP) 3/VP1. Screening for HEV was performed in parallel, as was detection of HPeV in respiratory and fecal surveillance samples, to identify virus types circulating in the general population.

RESULTS

HPeV was detected in 14 CSF samples obtained exclusively from young infants (age, <3 months) with sepsis or pyrexia. The frequency of detection of HPeVs varied greatly by year, with the highest frequency (7.2%) noted in 2008 exceeding that of HEVs. Direct typing of CSF samples revealed that all infections were caused by HPeV type 3, a finding that is in contrast to the predominant circulation of HPeV1 in contemporary respiratory and fecal surveillance samples.

CONCLUSION

HPeV was a significant cause of severe sepsis and fever with central nervous system involvement in young infants, rivaling enteroviruses. The specific targeting of young infants by HPeV type 3 may reflect a difference in tissue tropism between virus types or a lack of protection of young infants by maternal antibody consequent to the recent emergence of HPeV.

Prevalence, clinical presentations and complications among hospitalized children with influenza pneumonia

Viral respiratory tract infections are a major cause of hospitalization in children. Influenza is common but often not laboratory proven. We report a prospective study of children admitted with a clinical diagnosis of pneumonia. Infants and children (ages 1 month-15 years) who were hospitalized with community-acquired pneumonia were enrolled in the study. Their nasopharyngeal aspirated samples were analyzed for common respiratory viruses, including influenza virus, by reverse transcription-polymerase chain reaction (RT-PCR) or PCR. Out of 257 patients, we identified 127 (49.4%) cases with respiratory viruses, and influenza was found in 32 of these cases (12.5%). Other common respiratory viruses included respiratory syncytial virus in 42 (16.3%), human metapneumovirus in 24 (9.3%), adenovirus in 17 (6.6%) and parainfluenza virus in 12 (4.7%). The median age of the influenza group was 2 years and 3 months, and 27 (84%) of children in this group were under the age of 5. Asthma was the most common co-morbidity (4/32, 12.5%). Common clinical presentations were fever and cough (100%) with crepitations (90%). The median length of hospitalization was 6 days. Three patients developed respiratory failure, with one mortality (3.1%). One child developed infection-associated hemophagocytic syndrome. Our study demonstrated that young children had a high risk of hospitalization due to influenza pneumonia, which contributed to a significant morbidity.