In a recent study published in IJID Regions, researchers explored the genetic diversity and prevalence of human metapneumovirus (hMPV) in pediatric respiratory infections, focusing on children under five years of age in Puducherry, India. This study aimed to enhance understanding and preparedness for respiratory viral outbreaks, especially with the emergence of new hMPV lineages, A2.2.1 and A2.2.2.
Background
Acute respiratory infections are a leading cause of childhood illness and mortality globally, particularly in low- and middle-income countries. hMPV is a significant contributor to these illnesses, affecting both the upper and lower respiratory tracts. The seasonal nature of hMPV infections was observed, with peaks in infection rates occurring during the winter-spring months, particularly in December and January.
hMPV is classified into two main groups, A and B, which are further divided into sub-lineages. Recent studies have shown that these lineages are evolving, but information on their genetic variability and prevalence, especially in specific regions like India, remains limited. The impact of the COVID-19 pandemic on hMPV spread is also under-explored, making it critical to assess the virus’s characteristics, prevalence, and co-circulation with other respiratory pathogens.
Study Overview
The study examined the genetic diversity and prevalence of hMPV in children under five years old in Puducherry, India, between January 2021 and June 2024. Children with influenza-like illnesses or acute respiratory infections were enrolled, and nasopharyngeal swabs were collected for viral RNA isolation. Reverse transcription polymerase chain reaction (RT-PCR) was used to screen for various respiratory pathogens, including hMPV, influenza, and respiratory syncytial virus (RSV).
During a hMPV outbreak between November 2022 and March 2023, the researchers analyzed samples with low cycle threshold values to study the genetic makeup of the virus, particularly the fusion protein gene. The genetic data were used to identify novel lineages and to predict how mutations in these lineages could impact immune evasion and antigenic stability.
Major Findings
The study found that hMPV significantly contributed to pediatric respiratory infections, with a positivity rate of 2.5% among 4519 samples. During the hMPV outbreak in late 2022 and early 2023, the virus was responsible for 43.1% of respiratory infections in children, making it the most prevalent pathogen during that period. The majority of cases occurred in children under one year old, with clinical symptoms including flu-like symptoms, wheezing, and respiratory distress, and severe cases presenting as pneumonia or bronchiolitis. Notably, the male-to-female ratio among affected children was 1.8:1.
Phylogenetic analysis revealed that most samples (91.89%) belonged to genotype A, with 8.11% from genotype B. Among genotype A, the study identified two novel sub-lineages, A2.2.1 and A2.2.2, which were characterized by unique amino acid substitutions and glycosylation changes. These mutations may influence the virus’s ability to evade the immune system and affect its pathogenicity. Substitutions like G42V, E96K, and M250R in lineage A2.2.2 were particularly notable, along with the identification of O-linked glycosylation at position 191, which may impact the virus’s antigenic properties.
Further analysis showed that hMPV infections were seasonal, peaking in December and January, in line with the typical seasonality of respiratory viruses. Co-circulation with other respiratory pathogens was observed, but co-infections were relatively rare. This study’s findings confirmed the genetic diversity of hMPV and highlighted the emergence of novel lineages, which could have important implications for disease severity, vaccine development, and public health strategies.
Conclusions
The study concluded that hMPV is a significant cause of respiratory infections in young children in India, particularly during seasonal peaks. The discovery of novel lineages A2.2.1 and A2.2.2 underscores the importance of continued surveillance to monitor genetic changes in the virus. The findings also suggest that these lineages may have implications for vaccine design and immune response.
Given the global nature of hMPV circulation, the emergence of these novel lineages calls for international collaboration in surveillance and research. Continued genetic monitoring and clinical studies are essential to understand the virus’s evolving patterns, improve diagnostic methods, and inform the development of targeted interventions to protect vulnerable populations.
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