OVERVIEW
Parainfluenza virus infection is a common acute viral respiratory tract infection that causes lower respiratory tract infections in infants and young children. In adults, it is mainly characterized by upper respiratory tract infections. According to statistics, 30% to 40% of acute respiratory tract infections in infants and children are caused by human parainfluenza viruses. About 33% of pediatric laryngitis and 10% of lower respiratory tract infections are associated with parainfluenza virus, second only to respiratory syncytial virus and adenovirus infections. Parainfluenza virus infections are prone to recurrent infections due to low immunity after infection.
Etiology
Parainfluenza viruses are named after certain biological traits and influenza-like symptoms when they were discovered. They have been isolated since 1953 and belong to the genus Paramyxovirus in the family Paramyxoviridae, with a classification of 1 to 4 types. Parainfluenza virus is spherical in shape, with a diameter of 125-250 nm, an envelope, and a single-stranded RNA. The virus can be isolated from primary monkey kidney cells or primary human embryonic kidney cells. It is also known as Sendai virus because it was isolated from a deceased child in Sendai, Japan.
Symptoms
The disease has an incubation period of 3 to 6 days. The severity of the disease is related to age, pathologic state, initial or recurrent infection, and virus type. The clinical manifestations caused by parainfluenza virus in childhood and adulthood vary greatly.
1. Childhood infection
Parainfluenza virus infection in young children mainly causes lower respiratory tract disease, acute onset, parainfluenza virus infection manifestations include fever, nasal congestion, sore throat, hoarseness, barking cough, large amount of mucopurulent sputum, wheezing and respiratory obstruction, and in severe cases, death may occur due to hypoxia and respiratory failure. There are obvious differences in clinical manifestations among the four serotypes of the virus. type 1 virus infection is the most likely to cause croup, with 6 months to 3 years of age as the most prevalent age group, and can also cause otitis media. type 2 virus infection also has croup as its main manifestation, but it is milder and rarer than type 1 infection, and is more prevalent from 8 months to 3 years of age. both type 1 and type 2 viral infections have a more acute onset, with nasal congestion, running nose, sore throat, and spasmodic barking-like coughing that develops after a variety of processes. Spasmodic barking cough, hoarseness, wheezing, triple concave sign and inspiratory dyspnea, or even cyanosis, mostly at night, and laryngeal obstruction in severe cases, which is caused by subglottic edema and thick secretion blocking the airway. 3-type viruses are more contagious, and infants infected in 1 year olds show capillary bronchitis and pneumonia with high fever, while toddlers in the age group of 1-3 years old show croup, and older children show bronchitis and bronchiolitis. In older children, tracheitis, bronchitis. Fever is often present for about 4 days in first-episode infections. In children with severe combined immunodeficiency, the incidence of type 3 virus infection is higher, and megaloblastic pneumonia may develop. otitis media is more common with type 3 virus infection than with type 1 virus infection, and type 4 virus infection is usually associated with mild respiratory symptoms and is not easily detected.
Parainfluenza virus infection can cause respiratory distress and hypoxia in infants and children, which can be life-threatening. In immunocompromised children, parainfluenza virus infection often causes chronic and progressive exacerbation of pneumonia. In addition, parainfluenza virus can trigger bronchial asthma or exacerbate asthma in children with existing bronchial asthma.
2. Adult infection
Regardless of the type of parainfluenza virus, infection in adults usually causes upper respiratory tract infections, such as rhinitis, pharyngitis, accompanied by discomfort, which may aggravate chronic bronchitis, chronic pharyngitis, chronic tonsillitis, etc. The elderly are prone to complications of pneumonia, and the immune system may also be affected. Elderly people are susceptible to pneumonia, and immunocompromised adults can also suffer from fatal pneumonia. Parainfluenza virus infection is also an important cause of lethal pneumonia in allogeneic bone marrow transplant patients.
Examination
1. Virus isolation and identification
Nasopharyngeal rinse or nasopharyngeal swab specimens are usually used, inoculated with susceptible primary monkey kidney cells, primary human embryonic kidney cells or human amniocytes for culture.
2. Rapid pathogen diagnosis
Nasopharyngeal secretions can be smeared, and fluorescent antibodies against parainfluenza virus types 1 to 3 can be used to detect virus-specific antigens in the exfoliated epithelial cells. In addition, PCR (Polymerase Chain Reaction) is a rapid and sensitive method for detecting nucleic acids of various types of parainfluenza viruses.
3. Serologic tests
Neutralization test, complement binding test and hemagglutination inhibition test can detect serum specific IgG (immunoglobulin G) type antibodies, and it is diagnostic value to have a 4-fold or higher antibody potency in both acute and recovery phases of the serum. Detection of serum specific IgM (immunoglobulin M) type antibodies in the acute phase by enzyme-linked immunosorbent assay is helpful for early diagnosis. However, each reinfection can lead to recalled elevations of other types of viral antibodies, so a single serologic test result should be used only for reference.
Diagnosis
Clinical diagnosis is easier during epidemics of parainfluenza virus infection and more difficult in disseminated cases. Preliminary diagnosis can be made on the basis of epidemiologic and clinical data. Definitive diagnosis depends on virus isolation and serologic testing.
Treatment
The principle is symptomatic, supportive treatment and prevention of secondary infection.
1. Keep the respiratory tract unobstructed
For laryngitis, wheezing with dyspnea, oxygen inhalation, sputum, asthma, nebulized inhalation to reduce local edema, severe cases can be short-term use of adrenocorticotropic hormone, respiratory failure, if necessary, tracheal intubation or tracheotomy. Cold humid air can reduce respiratory mucosal edema, promote secretion discharge, cold fog therapy can be used to facilitate the relief of clinical symptoms. Attention should be paid to the prevention and treatment of secondary bacterial infections.
2. Anti-infection
Antiviral therapy should be applied early to shorten the detoxification time and reduce the symptoms. For parainfluenza virus infection, ribavirin can be used by nebulized inhalation, oral or intravenous injection; α-interferon can be nebulized by inhalation or intramuscular injection; and thymosin can be used to enhance the ability of antiviral therapy. Antibiotics can be given when the disease is serious or when there is clear bacterial infection.
3.Supportive therapy
Plasma transfusion, intravenous human immunoglobulin, etc.
Prevention
Avoid contaminants and contact with patients, and pay attention to room disinfection and air circulation. Polyvalent and monovalent inactivated vaccines can produce serum antibodies, and the effect of spray immunization with live attenuated vaccines is under observation.