Respiratory viruses

The respiratory tract is the gateway for human breathing. In the season of viral epidemics, it is very easy to be infected with various viruses. Most of these viruses enter the body through the respiratory tract. Respiratory viruses have a wide range. Almost all viruses that infect the body are related to respiratory viruses. This virus is initially only on the surface of the respiratory tract and then transmitted into the human body, seriously endangering people's health. Lead to some serious diseases.

Respiratory virus is not a concept or a single virus. It is a general term for various viruses. It can be said that this was the early name for most viruses. Most of these viruses will invade various organs, causing certain harm to the human body and affecting normal work and study. The following is an introduction to what viruses respiratory viruses may develop into.

(I) Rhinoviruses are a subgroup of the picornavirus group. They are non-enveloped single-stranded RNA viruses with a diameter of 15 to 30 nm. They are resistant to ether but not acid and can survive for three days in a dry environment. According to serum neutralization tests, there are more than 120 serotypes, and 89 of them have been officially named. They grow best when cultured in diploid cells at 33°C under rotating conditions, can survive for a long time at -70°C, and can survive for several weeks at 4°C. They can be inactivated by heating at 56°C for 30 minutes.

Rhinovirus is the main cause of the common cold in humans. According to foreign statistics, it accounts for 15% to 40% of colds in adults. In 1973, viral infection ranked first among adult colds and acute attacks of chronic bronchitis in the elderly in Beijing and other places. The incidence rate in children is higher than that in adults. This disease can occur throughout the year, especially in late winter and early spring. Because the antigenicity of rhinoviruses is constantly changing and new types are constantly emerging, repeated infection is likely, and different types of strains can be prevalent in the population at the same time. Infection is through person-to-person contact, or contact with objects, through the nasal mucosa or conjunctiva.

(2) Coronavirus was isolated from a cold patient in 1968. It belongs to the coronavirus group and is an enveloped, single-stranded RNA virus that is sensitive to both ether and acid. It has a diameter of 80 to 150 nm and has unique rod-shaped peplomers protruding from the capsule. It proliferates in the cytoplasm and matures through budding from the cytoplasmic reticulum. At least three strains (B814, 229E and OC43) can cause respiratory infections in humans. Among them, 229E and OC43 are the causes of upper respiratory tract infections in children and adults, accounting for about 10% to 20% of common colds in adults, and occasionally can cause pneumonia and epidemic chest pain. This group of viruses is difficult to culture, and the etiological diagnosis relies on serological tests, such as complement fixation test (229E, OC43), hemagglutination inhibition test (OC43), ELISA (229E), RIA (OC43), etc.

(3) Influenza virus, see “Influenza”.

(4) Parainfluenza virus: This virus was first isolated in 1953 from the lung fluid of a child who died of pneumonia in Sendai, Japan. It was named Sendai virus at the time. Since it has many characteristics different from influenza, other strains were subsequently isolated, so it was named parainfluenza virus. This group of viruses belongs to the genus Paramyxovirus, which is an enveloped, single-stranded RNA virus with a diameter of 150-300nm. Currently, there are four serotypes: 1, 2, 3, and 4. Type 4 can be divided into two subtypes, A and B. It can be cultured in primary monkey kidney cells or primary human embryonic kidney cells.

Isolate this virus. Parainfluenza virus has hemagglutinin and hemolysin on its surface. The latter has a cytolytic effect and can dissolve the red blood cells of certain animals. It has a cytolytic effect and is related to the infectivity of the virus. The former can agglutinate the red blood cells of certain mammals and birds.

Parainfluenza virus infection only invades the surface tissue of the respiratory tract and proliferates in the epithelial cells. The resulting immune response is weak and prone to reinfection. It usually causes mild respiratory tract infections in adults, while children under 5 years old have a high incidence and severe illness, manifested as acute obstructive laryngobronchitis and pneumonia. A serological survey of children in Shanghai found that the positive rate of antibodies to parainfluenza types 1, 2, 3, and 4B in 4-year-old children reached 85% to 90%, and as high as 90% to 100% at the age of 5. Parainfluenza virus infection is not uncommon in children, second only to syncytial virus and adenovirus. The incubation period is 2 to 7 days. The virus can be isolated within 1 week of onset. Early antigens can also be detected by IFT, RIA, EIISA and other methods, with a positive rate of 75% to 95%. Currently, dot hybridization or polymerase chain reaction can be used to determine antigens. Serological tests were not used because of cross-reactions (type 4 and mumps virus) and the presence of repeated infections.

(5) Adenovirus was isolated from human proliferative cell culture in 1953. It is a non-enveloped, double-stranded DNA virus that replicates in the nucleus. It has a diameter of 70 to 90 nm, icosahedral symmetry, and is relatively stable at low temperatures of -20°C. 41 serum strains have been isolated from humans, and there are still many intermediate strains, which can manifest clinically as various types of diseases, such as respiratory tract infection, pneumonia, cystitis, encephalitis, keratitis, diarrhea, etc. This group of viruses can be transmitted through fecal-oral transmission, as well as through droplets, furniture, contaminated swimming pool water, or transplanted organs. The incubation period is 2 to 14 days. The virus can be isolated from respiratory secretion specimens, eye swabs, throat swabs or feces. The virus antigen can also be measured by IFT, RIA or ELISA to make a rapid diagnosis. The positive rate in patients with positive virus isolation is 60% to 65%. Neutralizing antibodies, hemagglutination inhibition antibodies and complement fixing antibodies can appear 7 days after infection. The diagnosis can be confirmed by serological determination of antibodies.

(VI) Respiratory syncytial virus: It was first isolated from an orangutan with respiratory tract infection in the laboratory in 1950. It is an enveloped single-stranded RNA virus with a diameter of 120 to 200 nm. It belongs to the genus Pneumovirus of the family Paramyxoviridae and has only one serotype. This virus is extremely unstable. Its titer drops 100-fold within 2 days at room temperature and 100-fold within 4 to 6 days in a 4°C refrigerator. It is the pathogen of lower respiratory tract infection (bronchiolitis-pneumonia), which is more common in children under 2 years old. It occurs throughout the year, but is more common in autumn and winter.

The pathogenesis is unclear. Even if infants and young children have neutralizing antibodies from the body, they can still develop severe respiratory diseases after infection, and repeated infection is common. Although children or adults have neutralizing antibodies, they cannot prevent the occurrence of the disease. For example, the presence of IgA antibodies locally in the respiratory tract can prevent infection. However, young children generally lack IgA antibodies locally in the respiratory tract. IgA increases slightly in the early stages of infection and gradually decreases in the late stages, so it is easy to cause repeated infections. Infection in adults presents with mild upper respiratory tract illness, but it can also cause serious illnesses such as pneumonia in the elderly.

The virus is transmitted through direct contact and droplets between people. The virus can be isolated within 3 to 5 days of onset. Human cells, diploid cells or primary monkey kidney cells are generally used for virus isolation. ELISA and IFT methods can also be used to detect viral antigens in respiratory secretions. The positive rate in cases confirmed by virus isolation is 85% to 90%. Available

Serological examination of specific IgA in nasopharyngeal secretions can be used for early diagnosis of the disease, but early elevation of specific IgM is not suitable as a basis for diagnosis of respiratory syncytial virus infection in infants and young children.

(VII) Enterovirus: Belongs to the genus Enterovirus of the family Picornaviriclae. It is a non-enveloped, ether-resistant RNA virus with a diameter of 20 to 30 nm. This group of viruses includes poliovirus (3 types), coxsackievirus (24 types in group A and 6 types in group B) and echovirus (34 types), totaling 67 types. The main viruses are coxsackie A21, B3 and echo11, 9, 20, etc. In addition, enterovirus type 68 among types 68 to 71 can also cause respiratory diseases.

(8) Other viruses such as reovirus types 1 to 3, herpes simplex virus type 1 and Epstein-Barr virus can cause upper respiratory tract infection and pharyngitis; measles, rubella and chickenpox all have symptoms of upper respiratory tract infection before the rash appears; mumps virus infection also has symptoms of upper respiratory tract infection before the typical clinical manifestations occur.

The above viruses are all relatively common respiratory viruses. I hope this can help you better understand the virus. In order to reduce the infection of respiratory viruses in the human body, we must pay attention to the rationalization of daily life. During the epidemic period of the virus, try not to go to crowded and poorly ventilated places. Keep the room well ventilated, change air frequently, drink plenty of boiled water, and eat more vegetables and fruits. You can also enhance your immunity through physical exercise to avoid virus invasion.