Human metapneumovirus in the preterm neonate: current perspectives

Epidemiological and Clinical Characteristics of Human Metapneumovirus-Associated Acute Respiratory Tract Infection Cases in the Pudong New Area, Shanghai, from 2014 to 2023

BACKGROUND

This study characterized Human metapneumovirus (HMPV) infection epidemiology and clinical features in patients with acute respiratory infections (ARIs) in Pudong New Area, Shanghai, China, compared by pre- and post-COVID-19 periods.

METHODS

Between January 2014 and December 2023, the basic and clinical information, as well as respiratory tract specimens from ARIs, were collected at 14 sentinel hospitals in Shanghai Pudong. Specimens were tested for HMPV and other respiratory pathogens. The positivity rates were analyzed by age, period (pre- and post-COVID-19), season, and case type. Clinical characteristics of HMPV-infected versus non-infected cases were compared.

RESULTS

14,488 ARI patients were enrolled, with a 1.77% HMPV-positive rate (257/14,488). Among the age groups, the highest positive rate was 5.39% (11 /204) in the 6-11-month age group, and all the HMPV-positive cases in the 6-11-month-old age group were inpatients. Among the < 6 months old, 1-2 years old, 3-5 years old, 6-14 years old, 15-64 years old, and ≥ 65 years old groups, the positivity rates were 1.92% (6/313), 2.92% (23/788), 2.21% (33/1494), 1.08% (25/2311), 1.46% (94/6443) and 2.21% (65/2935), respectively. HMPV-positive patients showed higher proportions of cough (p < 0.001), runny nose (p = 0.048), and sore throat (p = 0.0175) than HMPV-negative patients in children. Compared to HMPV-negative patients, there was a significant difference in pneumonia diagnosis in both children and adults (p < 0.001, p = 0.004). Before COVID-19, HMPV infection peaks occurred mainly in February and March. In October 2023, a significant peak (4.37%, 10/229) was observed.

CONCLUSIONS

Young children and elderly individuals are at higher risk for HMPV infection, with a reversal of seasonal patterns observed post-COVID-19. Surveillance of HMPV in children and the elderly is crucial for future epidemic Preparedness.

PD-1 signaling in neonates restrains CD8+ T cell function and protects against respiratory viral immunopathology

Respiratory viral infections, including human metapneumovirus (HMPV), remain a leading cause of morbidity and mortality in neonates and infants. However, the mechanisms behind the increased sensitivity to those respiratory viral infections in neonates are poorly understood. Neonates, unlike adults, have several anti-inflammatory mechanisms in the lung, including elevated baseline expression of programmed death ligand 1 (PD-L1), a ligand for the inhibitory receptor programmed cell death protein 1 (PD-1). We thus hypothesized that neonates would rely on PD-1:PD-L1 signaling to restrain antiviral CD8 responses. To test this, we developed a neonatal primary HMPV infection model using wild-type C57BL/6 (B6) and Pdcd1-/- (lacking PD-1) mice. HMPV-infected neonatal mice had increased PD-L1/PD-L2 co-expression on innate immune cells but a similar number of antigen-specific CD8+ T cells and upregulation of PD-1 to that of adult B6 mice. Neonatal CD8+ T cells had reduced interferon-gamma (IFN-γ), granzyme B, and interleukin-2 production compared with B6 adults. Pdcd1-/- neonatal CD8+ T cells had markedly increased production of IFN-γ and granzyme B compared with B6 neonates. Pdcd1-/- neonates had increased acute pathology with HMPV or influenza. Pdcd1-/- neonates infected with HMPV had long-term changes in pulmonary physiology with evidence of immunopathology and a persistent CD8+ T-cell response with increased granzyme B production. Using single-cell ribonucleic acid sequencing from a child lacking PD-1 signaling, a similar activated CD8+ T-cell signature with increased granzyme B expression was observed. These data indicate that PD-1 signaling critically limits CD8+ T-cell effector functions and prevents immunopathology in response to neonatal respiratory viral infections.

Neonatal Immune Responses to Respiratory Viruses

Respiratory tract infections are a leading cause of morbidity and mortality in newborns, infants, and young children. These early life infections present a formidable immunologic challenge with a number of possibly conflicting goals: simultaneously eliminate the acute pathogen, preserve the primary gas-exchange function of the lung parenchyma in a developing lung, and limit long-term sequelae of both the infection and the inflammatory response. The latter has been most well studied in the context of childhood asthma, where multiple epidemiologic studies have linked early life viral infection with subsequent bronchospasm. This review will focus on the clinical relevance of respiratory syncytial virus (RSV), human metapneumovirus (HMPV), and rhinovirus (RV) and examine the protective and pathogenic host responses within the neonate.

Role for Maternal Asthma in Severe Human Metapneumovirus Lung Disease Susceptibility in Children

Background

Severity of human metapneumovirus (hMPV) lower respiratory illness (LRTI) is considered similar to that observed for respiratory syncytial virus (RSV). However, differences in severity between these pathogens have been noted, suggesting the degree of illness may vary in different populations. Moreover, a potential association between hMPV and asthma also suggests that hMPV may preferentially affect asthmatic subjects.

Methods

In a population-based surveillance study in children aged <2 years admitted for severe LRTI in Argentina, nasopharyngeal aspirates were tested by RT-PCR for hMPV, RSV, influenza A, and human rhinovirus.

Results

Of 3947 children, 383 (10%) were infected with hMPV. The hospitalization rate for hMPV LRTI was 2.26 per 1000 children (95% confidence interval [CI], 2.04–2.49). Thirty-nine (10.2%) patients infected with hMPV experienced life-threatening disease (LTD; 0.23 per 1000 children; 95% CI, .16–.31/1000), and 2 died (mortality rate 0.024 per 1000; 95% CI, .003–.086). In hMPV-infected children birth to an asthmatic mother was an increased risk for LTD (odds ratio, 4.72; 95% CI, 1.39–16.01). We observed a specific interaction between maternal asthma and hMPV infection affecting risk for LTD.

Conclusions

Maternal asthma increases the risk for LTD in children <2 years old hospitalized for severe hMPV LRTI.

Intraoperative Acute Respiratory Failure in an Immunocompromised Patient with Human Metapneumovirus

Patient: Male, 31

Final Diagnosis: Pneumonia from Human Metapneumovirus pulmonary infection

Symptoms: Cough • fatigue

Medication: —

Clinical Procedure: Hernia repair

Specialty: Anesthesiology