Human metapneumovirus (hMPV) is a viral disease accompanied by damage to the upper and lower respiratory tract. More often it occurs in the form of acute respiratory infections with hyperemia of the pharynx, runny nose, cough, fever. In children and weakened patients, metapneumovirus causes bronchitis, bronchiolitis, bronchopneumonia. Virological diagnostics includes PCR of a nasopharyngeal smear, ELISA, lung X-ray, clinical and biochemical blood tests are additionally performed. Treatment of hMPV infection is symptomatic, antiviral, bronchodilator and mucolytic drugs are used.
ICD 10
B97.8 Human metapneumovirus
General information
Human metapneumovirus is a widespread acute respiratory viral infection caused by human metapneumovirus (hMPV, MPV). The virus was isolated in the Netherlands in 2001, but it is assumed that before that it had already been circulating in the population for at least 50 years. Metapneumovirus is common on all continents, people of all ages are susceptible to it, especially young children and the elderly. It is believed that by the age of 5, almost every child, and by the age of 10– absolutely all children carry a human metapneumovirus. In nasopharyngeal smears of children with symptoms of acute respiratory infections, metapneumovirus is detected in 3-16% of cases (according to some authors – up to 33-36%).
Causes
Metapneumovirus is a single–stranded RNA genomic virus belonging to the pneumovirus subfamily, the paramyxovirus family, and the pneumovirus genus. In its structure and properties, the pathogen is close to avian pneumovirus, a respiratory syntial virus. Viral particles have spherical, filiform or pleomorphic shape, diameter 209 nm. Virion RNA is enclosed in a thick lipid envelope, encodes 9 proteins.
Two genotypes of hMPV (A and B) are known, each of them has 2 subtypes that can circulate in the population simultaneously during one epidseason. Seasonal increases in the incidence of human metapneumovirus in the middle latitudes are recorded in winter and early spring.
Transmission paths
The leading pathway for the spread of human metapneumovirus is airborne. This virus has not been isolated from any animal species, so the only source is an infected person. Epidemic outbreaks are registered within the family, organized children’s groups, the occurrence of nosocomial foci of human metapneumovirus is possible.
Risk groups
Susceptibility to metapneumovirus is universal, however, the most severe lesions of the respiratory tract and complicated course of infection are observed in the following population groups:
- premature infants (especially with ENMT at birth);
- newborns with bronchopulmonary dysplasia;
- children of the first 3 years of life;
- elderly people;
- persons with immunodeficiency;
- patients with cystic fibrosis.
An unfavorable premorbid background in children is a burdened allergic history (drug and food allergies, exudative diathesis, atopy), neurological disorders (perinatal encephalopathy, increased ICP, muscular dystonia, febrile seizures), hematological changes (anemia), early initiation of artificial feeding.
Pathogenesis
The pathophysiological aspects of human metapneumovirus have not been sufficiently investigated to date. About 80% of cases of infection occur in the form of monoinfection, the remaining 20% ‒ in the form of a mixed infection: MPV + RS virus (36%), MPV + adenovirus (36%), MPV + rhinovirus (18%), MPV + coronavirus (9%), MPV + HCV-6.
Metapneumovirus replication occurs in the epithelial cells of the respiratory tract. Interacting with Toll-like cellular receptors, the MPV G-protein initiates the production of pro-inflammatory cytokines and chemokines with the development of a local inflammatory response. In the area of inflammation, there is an increase in the permeability of the epithelium and vascular endothelium, submucosal infiltration of the bronchi by eosinophils, neutrophils, macrophages, mast cells. The secretion of viscous mucin increases, mucociliary clearance is disrupted, bronchoconstriction occurs.
Studies show that human metapneumovirus is able to block the synthesis of gamma interferon, persist for a long time in the epithelium of the respiratory tract and nerve fibers with subsequent reactivation with a decrease in immunity. Thus, the course of human metapneumovirus can become chronic.
Human metapneumovirus symptoms
The incubation period lasts 3-5 days. The range of clinical manifestations is variable. The most common human metapneumovirus occurs in the form of mild or moderate rhinopharyngitis, laryngitis, laryngotracheitis, acute and obstructive bronchitis, bronchiolitis, viral pneumonia are also common. Sometimes gastrointestinal tract damage develops in the form of gastritis or gastroenteritis.
MPV infection often manifests acutely. With nasopharyngitis, catarrhal phenomena (tickling and sore throat, hyperemia of the posterior pharyngeal wall), swelling and stuffiness of the nasal passages, rhinorrhea with mucous or mucopurulent discharge, cough, injection of the sclera. Fever can be subfebrile, febrile or pyretic in nature. Intoxication syndrome is expressed (headache, lethargy, myalgia), sometimes exanthema is present.
Some children have gastrointestinal dysfunction: regurgitation, vomiting, loose stools, hepatomegaly and splenomegaly are detected. Laryngitis and laryngotracheitis are characterized by a barking cough, hoarseness of voice. The lesion of the lower respiratory tract is accompanied by the development of bronchoobstructive syndrome, shortness of breath (inspiratory, expiratory, mixed), cyanosis of the skin. With an uncomplicated course of human metapneumovirus, various symptoms persist on average from 4 to 13 days.
Complications
Complicated course of human metapneumovirus is typical for patients at risk. Bacterial infections of the lungs (pneumonia), ENT organs (catarrhal otitis media, lacunar angina), eyes (purulent conjunctivitis), urinary tract infections are noted. Infectious cardiomyopathy may develop.
Children often have stenosing laryngitis (croup). With obstructive bronchitis and bronchiolitis, respiratory insufficiency of varying severity is noted. The connection of human metapneumovirus with the subsequent development of bronchial asthma was noted.
Diagnostics
Children with human metapneumovirus are examined and treated by a pediatrician, adults by a therapist. In severe cases, consultation and observation of a hospital infectious disease specialist is indicated. An objective examination reveals hyperemia of the pharynx, auscultation – hard breathing, dry whistling and / or wet wheezing of various sizes. To confirm the clinical diagnosis , the following methods are used:
- Methods of pathogen detection. A highly accurate way to confirm MPV infection is PCR with reverse transcription. The material for the study is smears from the nasopharynx, bronchoalveolar lavage. As a retrospective method to confirm the transferred infection, ELISA is performed (detects an increased titer of antibodies to metapneumovirus).
- Other tests. Changes in the blood test are characteristic of any inflammatory reaction: moderate lymphocytosis, monocytosis, increased ESR. In the urine of children, leukocyturia and proteinuria are sometimes detected. Of the biochemical indicators, the high level of CRP attracts attention. Additionally, it may be necessary to sow the separated oropharynx and nasopharynx for flora, virological examination of feces.
- Lung X-ray. For uncomplicated human metapneumovirus, an increase in the pulmonary pattern is typical. With pneumonia, focal and infiltrative changes in lung tissue are determined.
Differential diagnosis
Differential diagnostic measures for human metapneumovirus are usually not required. Only in some cases it becomes necessary to exclude other viral infections occurring with nasopharyngitis, laryngotrecheitis syndromes:
- respiratory syncytial infection;
- adenovirus infection;
- bokavirus infection;
- parainfluenza;
- influenza.
Human metapneumovirus treatment
Hospitalization is more often required for young children with bronchitis, bronchiolitis, pneumonia of metapneumovirus etiology. The remaining patients are treated on an outpatient basis. Bed rest is prescribed for the entire feverish period. They recommend a dairy-vegetable, fortified diet, abundant drinking (tea, fruit drinks, mineral water).
Etiotropic therapy has not been developed. Interferon preparations and its inducers are used in the treatment, in severe cases ‒ intravenous immunoglobulins. With pronounced catarrhal phenomena, gargle, nasal shower, instillation of vasoconstrictive drops into the nasal passages are carried out. To facilitate the evacuation of mucus from the bronchi and relieve bronchospasm, inhalations are carried out.
The use of antipyretics, bronchodilators, mucolytics, antihistamines is indicated. In case of secondary complications of human metapneumovirus, antibiotics, bronchodilators, infusion detoxification, and oxygen therapy are added to the treatment regimen.
Prognosis and prevention
Mild and moderate cases of human metapneumovirus end in recovery within 1-2 weeks. Bacterial complications, respiratory failure are observed in children and adults with a burdened premorbid background, mixed infection. Specific vaccine prophylaxis of metapneumovirus infection has not been developed. As with other acute respiratory infections, it is recommended to observe therapeutic and protective measures: isolate the patient, ventilate the room, wear a medical mask in crowded places.
