The role of human Metapneumovirus genetic diversity and nasopharyngeal viral load on symptom severity in adults

Abstract

Background: Human metapneumovirus (HMPV) is established as one of the causative agents of respiratory tract infections. To date, there are limited reports that describe the effect of HMPV genotypes and/or viral load on disease pathogenesis in adults. This study aims to determine the role of HMPV genetic diversity and nasopharyngeal viral load on symptom severity in outpatient adults with acute respiratory tract infections.

Methods: Severity of common cold symptoms of patients from a teaching hospital was assessed by a four-category scale and summed to obtain the total symptom severity score (TSSS). Association between the fusion and glycoprotein genes diversity, viral load (quantified using an improved RT-qPCR assay), and symptom severity were analyzed using bivariate and linear regression analyses.

Results: Among 81/3706 HMPV-positive patients, there were no significant differences in terms of demographics, number of days elapsed between symptom onset and clinic visit, respiratory symptoms manifestation and severity between different HMPV genotypes/sub-lineages. Surprisingly, elderly patients (≥65 years old) had lower severity of symptoms (indicated by TSSS) than young and middle age adults (p = 0.008). Nasopharyngeal viral load did not correlate with nor predict symptom severity of HMPV infection. Interestingly, at 3-5 days after symptom onset, genotype A-infected patients had higher viral load compared to genotype B (4.4 vs. 3.3 log₁₀ RNA copies/μl) (p = 0.003).

Conclusions: Overall, HMPV genetic diversity and viral load did not impact symptom severity in adults with acute respiratory tract infections. Differences in viral load dynamics over time between genotypes may have important implications on viral transmission.

Keywords: Acute respiratory tract infection; Genetic diversity; Human metapneumovirus (HMPV); Symptom severity; Viral load.

Fig. 1

Phylogenetic analysis of a) 85 fusion (F) and b) 82 attachment (G) genetic sequences. Maximum-likelihood trees were reconstructed using PAUP version 4.0. The reliability of the branching nodes was assessed by bootstrap analysis of 1000 replicates. Bootstrap values of greater than 70% were indicated on the branch nodes. The generated sequences (dark circles) were named according to the country of isolation (Malaysia, MY), unique sample ID and year of sample collection. Published HMPV reference strains for each genotype/sub-lineage (blue triangles) included A1, NL00–1 (GenBank accession number: AF371337.1), A2a, CAN97–83 (AY297749.1), A2b, JPS03–240.1 (AY530095), B1, NL/1/99 (AY525843.1), and B2, CAN98–75 (AY297748.1). Other published sequences included those from Australia (AUS), Cambodia (CAMB), Canada (CA), India (IND), Japan (JP), Netherlands (NL), Peru (PER), Singapore (SIN), Thailand (TH), United States (USA), and Vietnam (VIET)

Fig. 2

Viral load at different periods of enrollment after symptom onset. a) total HMPV-infected patients, b) patients with different symptom severity, c) patients infected with different HMPV genotypes and d) patients infected with different HMPV sub-lineages