Pediatric parainfluenza virus pneumonia

　　1. Etiology

　　Parainfluenza virus belongs to the Paramyxoviridae family, an RNA virus. The parainfluenza viruses related to humans are divided into 4 types: Type 1 has two strains, namely the hemagglutinin 2 virus (HA2) and Sendai virus (HVJ); Type 2 is the croup virus (CA); Type 3 is the hemagglutinin 1 virus (HA1); Type 4 also has two strains, A and B (M25). Types 1, 2, and 3 can cause mild rhinitis, pharyngitis, and bronchitis; Types 1 and 2 can cause severe laryngitis (croup), which is more common in children aged 2 to 6 years; Type 3 can cause pneumonia and bronchiolitis, which is more common in infants under 1 year of age. As for the Sendai virus, there were a few reports of pneumonia caused by it in Japan in 1952 and 1953, and in Vladivostok, the Soviet Union, in 1955, but there is doubt abroad about its ability to cause human disease. In China, the antibody level in the convalescent phase of infants and young children with pneumonia, bronchiolitis, and upper respiratory tract infection caused by Sendai virus was found to be more than 4 times higher in Beijing, and the virus was isolated. Therefore, the pathogenicity of Sendai virus to humans should be confirmed. As a viral pathogen of pneumonia and bronchiolitis in infants and young children, parainfluenza virus has been the third most common in the north after respiratory syncytial virus and adenovirus in recent years, and the second most common after respiratory syncytial virus in the south.

　　2. Pathogenesis

　　Parainfluenza virus is mainly transmitted through respiratory secretions and can spread through aerosols in the air. Parainfluenza virus is relatively active in cold and dry environments, therefore, infections with parainfluenza virus are more common during winter and spring.

　　Parainfluenza virus pneumonia, due to the widespread presence of parainfluenza virus in nature, can occur throughout the year and can cause varying degrees of upper and lower respiratory tract infections in children, such as common cold, otitis media, severe laryngitis, tracheitis, bronchitis, bronchiolitis, and pneumonia. Parainfluenza virus pneumonia is similar to respiratory syncytial virus pneumonia and is relatively common in infantile pneumonia. It can be complicated by bacterial infection, but generally has no other complications. Children with poor immunity may develop complications such as meningitis after infection. Small infants may suffocate and develop respiratory failure due to acute laryngotracheobronchitis.

　　From 1962 to 1964, the symptoms of Sendai virus pneumonia observed in Beijing, with a fourfold increase in convalescent serum antibodies, were: fever for 1 to 8 days, most commonly 3 to 5 days, with a short duration of high fever, mild cough, only a few cases with laryngitis, mild respiratory distress, scattered rales in the lungs, but the vast majority of percussion did not produce dullness. X-ray examination showed small areas of shadow, which absorbed within 1 to 3 weeks. Individual cases of pneumonia caused by other subtypes of parainfluenza virus were also observed, with symptoms similar to those caused by Sendai virus. From 1975 to 1980, the Institute of Pediatrics of the Chinese Academy of Medical Sciences found that serum antibodies increased fourfold or more in mainly type 3 parainfluenza virus, with a few cases of type 2 and Sendai virus. The clinical manifestations of these infantile pneumonia cases were similar to those observed in 1962 to 1964. Most of the cases were mild. It was reported abroad that the clinical manifestations of type 3 parainfluenza virus infection in infants under 1 year of age were extremely similar to those of respiratory syncytial virus infection. The onset was preceded by symptoms of common cold, runny nose, low fever, cough, followed by increased cough, sputum, accelerated breathing, dry and wet rales and wheezing in the lungs, and in cases with bacterial infection, high fever and severe toxic symptoms, obvious shortness of breath. Currently, it is difficult to make a specific diagnosis of parainfluenza in clinical practice. When necessary, virus isolation and identification can be performed through tissue culture inoculation, and immune and molecular biological techniques can be used to detect viral antigens in respiratory infected cells. Complement fixation tests and hemagglutination inhibition neutralization tests with acute and convalescent serum can confirm parainfluenza virus infection. However, without virus isolation, it is difficult to identify specific virus types due to serological cross-reactions.

　　The prevention of parainfluenza virus is roughly the same as that of SARS and influenza. It is necessary to develop good habits of preventing all respiratory infectious diseases and maintaining hygiene, such as frequent ventilation, exercise, hand washing, and drinking plenty of water, timely adjustment of clothing, wearing a mask when visiting patients, avoiding coughing and sneezing towards others, maintaining good personal and environmental hygiene, and enhancing the body's ability to resist various diseases. Some researchers in foreign countries are studying subunit vaccines, but they are still a certain time away from practical application. There is already a live vaccine for parainfluenza virus type 3 that can be used for preventive purposes.

　　Rapid diagnosis of viral antigens can be performed using direct or indirect immunofluorescence technology to detect nasopharyngeal secretions, or RIA, enzyme-labeled antibody staining method, or ELISA method can be used to detect. Confirmation requires viral isolation or serological examination. Healthy children rarely isolate the virus from the nasopharynx, so the isolation of the virus from the pharyngeal and nasal secretions can be determined as the etiology and perform virological diagnosis. The nasopharyngeal secretions or throat swab specimens of the children should be collected in the early stage of the disease, as the positive rate of monkey kidney cells is the highest, the lesions of type 1 and 3 appear within 3-7 days of culture, and can be identified by hemagglutination inhibition; the culture time of type 2 and 4 is longer, and only type 2 can be seen in fused cells. Serological diagnosis can be used by hemagglutination inhibition test, even if it is the first time the disease occurs, 1, 2, 3, and mumps virus homologous and heterologous antibodies may rise simultaneously; during reinfection, homologous and (or) heterologous antibodies may also rise; but sometimes, although the virus isolation from the nasopharyngeal secretions is positive, there is no rise in antibodies. The rise of antibody to type 4 virus is understood less, only known that homologous antibodies rise frequently during the first infection, clinical requirements for rapid diagnosis, rapid diagnosis during the acute phase can be used to detect antigens by smears of secretions or tissue immunofluorescence, or RIA, enzyme-labeled antibody staining method, complement fixation method, hemagglutination inhibition method, or ELISA method. X-ray shows increased pulmonary markings, punctate shadows in the lower lungs, overinflation of alveoli, and signs of consolidation can be seen in the case of bacterial infection.

　　Children's parainfluenza virus pneumonia generally has different dietary requirements based on the symptoms of different children, please consult a doctor for specific information, and formulate different dietary standards for specific patient conditions.

　　Treatment can refer to Respiratory Syncytial Virus Pneumonia, parainfluenza virus is effective for ribavirin (virazole) treatment. It is mainly symptomatic treatment, appropriate treatment is taken according to age and condition, and nebulized inhalation of adrenaline or β2 agonists can be used to improve ventilation in pediatric pneumonia. Ribavirin (virazole) has antiparainfluenza virus efficacy, intravenous infusion of 10-15mg/(kgd), divided into 2-3 times a day.