Measles virus pneumonia

　　1. Etiology

　　Measles is an acute infectious disease caused by the measles virus (measlesvirus), with the most common complication being measles virus pneumonia (measles pneumonia). The measles virus can invade the entire respiratory tract mucosa and cause pneumonia, which can occur during the pre-eruption and eruption stages of measles. Children with low immunity are often without rash and are prone to giant cell pneumonia. Due to widespread damage to the respiratory tract mucosa, bacterial infections often occur during the rash stage or post-rash period, most commonly in malnourished and weak children. The causative bacteria are commonly Streptococcus pneumoniae, Staphylococcus aureus, and Haemophilus influenzae, with Staphylococcus aureus being particularly common, and the condition is often severe. A few children may also have concurrent adenovirus infection. When measles is complicated with both bacterial and adenovirus infections, the condition becomes more severe, often being a major cause of death due to measles pneumonia.

　　2. Pathogenesis

　　The main pathological change of measles is the extensive fusion of cells to form multinucleated giant cells. The pathological manifestations of measles virus pneumonia include acute inflammation of respiratory tract epithelial cells, including bronchi and bronchioles, with edema, congestion, and necrosis that can form ulcers with cilium shedding, and the formation of mononuclear cells and multinucleated giant cells in the interstitium. The lesions involve the bronchiolar area, leading to interstitial pneumonia with mononuclear cell infiltration, mainly lymphocytes. Lesions in the lungs can coalesce, invade the reticuloendothelial system, causing lymphadenopathy. Multinucleated giant cells appear in the respiratory tract and alveolar walls, containing eosinophilic inclusions within the nuclei and cytoplasm, known as giant cell pneumonia. The alveoli are filled with degenerated epithelial cells, multinucleated cells, and mononuclear cells, with the alveolar walls forming a hyaline membrane. Bronchial secretions and desquamated cells can cause partial obstruction of the bronchi, leading to localized emphysema and complete obstruction can cause atelectasis. Concurrent bacterial infection can produce pathological changes of bronchopneumonia, and sometimes empyema or pyopneumothorax may occur. Chronic lesions can lead to bronchiectasis.

　　Bacterial pneumonia (bacterial pneumonia) accounts for 80% of pneumonia caused by various pathogens in adults. Since the era of antibiotics, the prognosis of bacterial pneumonia has significantly improved, but the mortality rate has remained high since the 1960s. Currently, bacterial pneumonia has some new characteristics, including changes in the spectrum of pathogens, especially a significant increase in the ratio of Gram-negative bacilli in hospital-acquired pneumonia. Streptococcus pneumoniae still occupies a dominant position in the pathogens of community-acquired pneumonia, but the clinical manifestations tend to be atypical. The increasing rate of bacterial resistance has led to frequent occurrences of 'difficult-to-treat' pneumonia, with extremely high mortality rates in children, the elderly, and immunosuppressed patients. Improving the level of pathogenic diagnosis, rationally using antibiotics, avoiding the emergence of drug-resistant bacteria, and improving supportive treatment are urgent issues that need to be emphasized and solved in the clinical management of pneumonia.

　　Pneumonia is the most common complication of measles, more common in infants and young children with low immunity, often occurring in the early stage of the disease. When pneumonia occurs, the respiratory symptoms of children with measles are significantly exacerbated, often with persistent high fever, severe cough, rapid breathing, flaring nostrils, cyanosis, and dry and wet rales in the lungs. These symptoms often subside with the disappearance of measles fever and skin rash, but malnutrition, weakness, and low immunity can lead to giant cell pneumonia, which often persists and may not improve. Fever may not subside during the rash phase or return after subsiding, with worsening respiratory symptoms, increased white blood cells, indicating a possible concurrent bacterial pneumonia. There is also a higher chance of empyema. In the past, those who had been vaccinated with inactivated measles vaccine may develop atypical measles syndrome (AMS) years later due to low antibody levels, which may also occur in those who have received attenuated live vaccine. Symptoms are atypical, often with severe systemic symptoms and few catarrhal symptoms, including high fever, headache, dry cough, abdominal pain, and myalgia. Mucosal patches are rarely seen, and rashes usually appear first on the extremities and then spread centrally. Pneumonia often occurs, and pleural effusion may develop. Lesions in the lungs may take several months to absorb. The pathogenesis of atypical measles syndrome is not yet clear and may be related to the patient's partial immunity and hypersensitivity to the measles virus. Inactivated measles vaccine is no longer used, and attenuated live measles vaccine is now used, so atypical measles syndrome is very rare.

　　The main measures are to isolate patients; for children, artificial active immunization is carried out to enhance the body's immunity. Measles attenuated live vaccine is widely used in most countries outside China, resulting in a significant decrease in the incidence of measles. China stipulates that the primary immunization is at 8 months of age, and a booster dose is given one year later and before school age. This vaccine is administered subcutaneously, with a seroconversion rate of over 90%, few side effects, and immunity that can last for about 10 years. For susceptible children who have not been vaccinated and have been in contact with measles patients, intramuscular injection of whole blood from healthy adults, serum from measles convalescents, or gamma globulin within 5 days after contact can have some preventive effect.

　　1. Nasopharyngeal secretions, sputum bacterial smear examination of sputum smears.

　　2. Hemagglutination inhibition and enzyme-linked immunosorbent assay (ELISA) for detection of measles IgG during the acute and convalescent phases, and complement fixation test for measles.

　　3. Antibody capture enzyme-linked immunosorbent assay (ELISA) for detection of measles IgM has high sensitivity and specificity, and is valuable for early diagnosis.

　　4. Chest X-ray examination shows diffuse bronchiolitis and interstitial lung inflammation in measles virus pneumonia. The inflammatory infiltration of pulmonary纹理性bacterial infection is often distributed in bronchopneumonia of the lung segments, usually located in the lower lobes of one or both lungs.

　　In addition to conventional treatment, the following aspects should be paid attention to in diet for measles virus pneumonia: diet should be light, pay attention to hygiene, and rationally match the diet. Avoid eating spicy and刺激性 food.

　　1. Treatment

　　Currently, there is no specific antiviral drug for the measles virus. General antiviral drugs such as ribavirin, when inhaled through a nebulizer or administered intravenously, have not been proven to have any definite efficacy. The treatment of measles virus pneumonia mainly includes symptomatic treatment, supportive therapy, and preventive treatment of complications. Appropriate antibiotics are used to prevent secondary bacterial infections. For patients with concurrent bacterial lung infections, antibiotics should be selected based on the pathogen and drug sensitivity tests. When laryngitis with laryngeal obstruction occurs, in addition to oxygen therapy, tracheal intubation or tracheotomy should be considered according to the condition to improve ventilation.

　　2. Prognosis

　　The mortality rate of measles pneumonia is relatively high. 20 years ago, the mortality rate of measles pneumonia was 60.1%, and it is still around 10% now.