Human Metapneumovirus Infection

The first reported cases of HMPV infection from Bengaluru, Karnataka, affecting two infants aged eight months and three months, raised concerns across the country. Those infants presented with features of bronchopneumonia on January 3, 2025. Subsequent investigations showed that they were HMPV positive. They recovered following symptomatic treatment. No travel history was recorded, and it appeared due to local transmission.³

Human Metapneumovirus is an example of a virus family that causes a severe respiratory tract infection. HMPV, a negative-sense, single-stranded RNA virus, belongs to the Paramyxoviride family including other respiratory viruses such as respiratory syncytial virus (RSV) and parainfluenza virus. The virus, which was named HMPV, was isolated in 2001 in the Netherlands by Bernadette van den Hoogen and her colleagues.⁴ The infection was seen in 28 young children. This unknown virus was grown in cultured cells obtained from infected airway epithelium using the RAP-PCR technique. The newly discovered virus had a genomic organization similar to the RSV. The virus attaches to the target cells via glycoprotein. Two genotypic groups, A and B, have been recognized. Based on the F sequence, they have been further subdivided into A1, A2, B1, and B2 lineages. Thus, it has shown marked genetic diversity.⁵ The HMPV is a seasonal disease occurring in the winter and early spring, similar to RSV.⁶ The organism has been found to circulate in many countries around the world. In an outbreak in Puducherry, India, between November 2022 and March 2023, 56 of 583(9.6%) children tested positive for HMPV infection. There was presence of genetic diversity with the presence of A2.2.1 and A2.2.2 sub-lineages highlighting the evolving nature of HMPV.⁷

The infection spreads from person- to- person through infected respiratory droplets, direct contact with an infected individual, or by touching contaminated surfaces such as furniture, utensils, beds, blankets, doors, windows, and door handles (fomite vectors). Notably, the infection primarily affects children under the age of five.

HMPV virus causes symptoms similar to the common cold, with clinical features appearing 3-6 days after an incubation period. The severity of symptoms varies depending on age, health status, and immune function. Common symptoms include cough, fever, sneezing, runny or stuffy nose, sore throat, body ache, and headache, which are generally mild and confined to the upper respiratory tract. However, occasionally the infection may progress to the lower respiratory tract, leading to cough, wheezing, and dyspnea, resembling influenza.

Severe illness can occur in young children, adults over 65 years, individuals with weak immune systems, or those with underlying conditions such as asthma or pulmonary diseases. In children, HMPV symptoms closely resemble those of RSV.

It is challenging to differentiate HMPV infection from other respiratory infections as they have similar symptoms. Molecular diagnostic testing helps to confirm the diagnosis. The viral genome or antigens may be detected by nucleic acid amplification test (NAAT), immunofluorescence or enzyme immunoassay, respectively. Commonly the etiology is confirmed by the use of RT-PCR that helps to amplify RNA extracted from respiratory secretions. Such investigative procedures, though rarely required, assist in confirming the etiology of the respiratory infection. People are aware of such a test during the Covid-19 epidemic.