HMPV is the first human member of the MetaPneumonia virus belonging to the family of Paramoxyviridae family. It is enveloped single stranded RNA virus. Phylogenetic analysis have revealed that there are two distinct phenotypes of HMPV which is A and B. These groups are further subdivided into lineages A2.2.1 and A2.2.2. Although research from around the world has shown how these lineages are changing, little is known about their frequency and genetic diversity, particularly in certain parts of India. This classification holds true for variability in the sequence of the glycoprotein F (Fusion) and G (attachment) binding sites leading to genetic diversity.
Though it can affect all age groups, elderly people and young are seen to be more at a risk. There are studies which have reported that aged mice has more susceptibility than the young mice and the viral clearance was also delayed in the aged mice. HMPV is thought to be transmitted through direct or close contact with saliva and infected droplets. It might be difficult to diagnose HMPV since its clinical symptoms frequently resemble those of other respiratory viruses. Fever, coughing, nasal congestion, sore throat, and dyspnea are typical symptoms. Severe cases of HMPV, especially in high-risk groups, may result in hospitalisation because of consequences including pneumonia or worsening of long-term illnesses like asthma and chronic obstructive pulmonary disease (COPD).
A significant outbreak of HMPV in china has sparked an international worry. The symptoms are very similar as cold or flu but are seen to be quite dangerous amongst the small infants and older people. A distinct seasonality pattern that is consistent with other respiratory viruses, especially during the winter-spring seasons, was revealed by the study, which also revealed that HMPV infections peaked in December and January.
One of the biggest challenges is that HMPV has not been diagnosed correctly because it has overlaps with other respiratory infections. Laboratory tests such as PCR and detection of antigen could be used to identify and confirm the presence of the virus. The majority of people recover from HMPV without any problems in 7–10 days. However, there is a greater chance of serious issues for these groups: Pneumonia, Bronchiolitis, Exacerbation of Chronic disorders, Asthma and chronic obstructive pulmonary disease (COPD) , Secondary Bacterial and Pregnancy Complications.
The persistence of the HMPV infection is due to the late immune response and also delayed activity of the cytotoxic T cell during the primary infection. HMPV interferes with the cytokines fluxes thus hindering the T cell activation and proliferation. HMPV has eight genes that code for 9 different proteins, which are responsible for infecting the host cells. The glycoprotein (G) protein helps in the attachment of the Fusion(F) protein which further binds to the transmembrane fusion via the integrins on the host cell surfaces in order to facilitate the entry into the host cell. This event causes the release of the chemokines and cytokines IL-6, TNF-α and IL-2 and accumulation of inflammatory cells specifically near the vascular area. Additionally, the inflammatory process causes monocytes and lymphocytes to infiltrate the airway endothelium. When these reactions come together, they cause pulmonary inflammation, which results in respiratory symptoms as fever, coughing, mucus production, and dyspnea. There is currently no treatment or vaccines available for HMPV, although certain management therapies could be adopted to alleviate and manage the symptoms.
References:
- Haas, L. E., Thijsen, S. F., van Elden, L., & Heemstra, K. A. (2013). Human metapneumovirus in adults. Viruses, 5(1), 87–110. https://doi.org/10.3390/v5010087
- https://bigapollospectra.com/blog/major-causes-of-lung-failure-examining-the-causes/
- Panda, S., Mohakud, N. K., Pena, L., & Kumar, S. (2014). Human metapneumovirus: review of an important respiratory pathogen. International journal of infectious diseases : IJID : official publication of the International Society for Infectious Diseases, 25, 45–52. https://doi.org/10.1016/j.ijid.2014.03.1394
- https://my.clevelandclinic.org/health/diseases/22443-human-metapneumovirus-hmpv
- https://euracare.com.gh/respiratory-medicine/
