Адам метапневмовирусы: түрі, таралуы және ауру тудыру қабілеті

Species of virus

Human metapneumovirus (HMPV or hMPV) is a negative sense single stranded RNA virus of the family Pneumoviridae and is closely related to the Avian metapneumovirus (AMPV) subgroup C. It was isolated for the first time in 2001 in the Netherlands by using the RAP PCR (RNA arbitrarily primed PCR) technique for identification of unknown viruses growing in cultured cells. As of 2016, it was the second most common cause (after respiratory syncytial virus (RSV)) of acute respiratory tract illness in otherwise healthy children under the age of 5 in a large US outpatient clinic. The peak age of hospitalization for infants with HMPV occurs between 6–12 months of age, slightly older than the peak of RSV, which is around 2–3 months. The clinical features and severity of HMPV are similar to those of RSV. HMPV is also an important cause of disease in older adults.

Human metapneumovirus was first discovered in 2001 in the Netherlands by Bernadette G. van den Hoogen and her colleagues. hMPV was first detected in the respiratory secretions of 28 young children in the Netherlands and had initially stood out from other common respiratory viruses because the testing methods van den Hoogen et al. had tried using (immunological assays using virus specific antibodies and PCR based methods using virus genome specific primers) were only able to test for known respiratory viruses and, therefore, were unable to identify the novel virus. The virus is distributed worldwide and, in temperate regions, has a seasonal distribution generally following that of RSV and influenza virus during late winter and spring. Serologic studies have shown that by the age of five, virtually all children worldwide have been exposed to the virus. Despite near universal infection during early life, reinfections are common in older children and adults. Human metapneumovirus may cause mild upper respiratory tract infection (the common cold). However, premature infants, immunocompromised persons, and older adults >65 years are at risk for severe disease and hospitalization. In some studies of hospitalizations and emergency room visits, HMPV is nearly as common and as severe as influenza in older adults. HMPV is associated with more severe disease in people with asthma and adults with chronic obstructive pulmonary disease (COPD). Numerous outbreaks of HMPV have been reported in long term care facilities for children and adults, causing fatalities.

The genomic organisation of HMPV is similar to RSV; however, HMPV lacks the non structural genes, NS1 and NS2, and the HMPV antisense RNA genome contains eight open reading frames in slightly different gene order than RSV (viz. 3’ N P M F M2 SH G L 5’). HMPV is genetically similar to the avian metapneumoviruses A, B and in particular type C. Phylogenetic analysis of HMPV has demonstrated the existence of two main genetic lineages termed subtype A and B containing within them the subgroups A1/A2 and B1/B2 respectively. Genotyping based on sequences of the F and G genes showed that subtype B was associated with increased cough duration and increased general respiratory systems compared to HMPV A.

hMPV is estimated to have a 3–6 day incubation period and is often most active during the later winter and spring seasons in temperate climates, overlapping with the RSV and influenza seasons and possibly allowing for repeated infection. With that being said, it has been determined that the first step of the hMPV replication cycle is attachment to the host cell, specifically the epithelial cells of the respiratory tract, using the G protein. then mediates fusion of the cell membrane and viral envelope in a pH independent fashion, likely within endosomes. HMPV then induces the response of chemokines and cytokines such as IL 6, IFN alpha, TNF alpha, IL 2, and macrophage inflammatory proteins, which in turn leads to peribronchiolar and perivascular infiltration and inflammation.

Though hMPV was first discovered and identified in 2001, serological studies showed that hMPV, or a close relative of it, had already been circulating for at least 50 years. From this information, it is clear that the virus had not just “jumped” from birds, or some other animal reservoir, to humans shortly before its discovery. HMPV has been shown to circulate during fall and winter months with alternating predominance of a single subtype each year. but ribavirin has shown effectiveness in an animal model. American pharmaceutical corporation Moderna has conducted a clinical trial for a candidate modRNA vaccine against metapneumovirus. As of October 2019, the vaccine candidate has passed through phase I, with reports that the vaccine is well tolerated at all dose levels at two months, and provokes an immune response which boosts the production of neutralising antibodies.

Human metapneumovirus was first reported in 2001 and avian metapneumovirus in the 1970s. There are at least four lineages of human metapneumovirus—A1, A2, B1 and B2. Avian metapneumovirus has been divided into four subgroups—A, B, C and D. Bayesian estimates suggest that human metapneumovirus emerged 119–133 years ago and diverged from avian metapneumovirus around 1800.