Human respiratory syncytial virus
Encyclopedia
Human respiratory syncytial virus (RSV) is a virus
that causes respiratory tract
infections. It is the major cause of lower respiratory tract infection
s and hospital visits during infancy and childhood. A prophylactic medication (not a vaccine
) exists for preterm birth (under 35 weeks gestation) infants and infants with a congenital heart defect
(CHD) or bronchopulmonary dysplasia
(BPD). Treatment is limited to supportive care, including oxygen therapy
.
In temperate climates there is an annual epidemic
during the winter months. In tropical climate
s, infection is most common during the rainy season.
In the United States, 60% of infants are infected during their first RSV season, and nearly all children will have been infected with the virus by 2–3 years of age. Of those infected with RSV, 2–3% will develop bronchiolitis
, necessitating hospitalization. Natural infection with RSV induces protective immunity which wanes over time—possibly more so than other respiratory viral infections—and thus people can be infected multiple times. Sometimes an infant can become symptomatically infected more than once, even within a single RSV season. Severe RSV infections have increasingly been found among elderly patients.
RSV is a negative-sense, single-stranded RNA virus
of the family Paramyxoviridae, which includes common respiratory viruses such as those causing measles
and mumps
. RSV is a member of the paramyxovirus subfamily Pneumovirinae. Its name comes from the fact that F proteins on the surface of the virus cause the cell membranes on nearby cells to merge, forming syncytia.
s and minor illnesses. The Centers for Disease Control consider RSV to be the "most common cause of bronchiolitis (inflammation of the small airways in the lung) and pneumonia
in children under 1 year of age in the United States".
For some children, RSV can cause bronchiolitis
, leading to severe respiratory illness requiring hospitalization and, rarely, causing death. This is more likely to occur in patients that are immunocompromised or infants born prematurely
. Other RSV symptoms common among infants include listlessness, poor or diminished appetite, and a possible fever.
Recurrent wheezing and asthma
are more common among individuals who suffered severe RSV infection during the first few months of life than among controls; whether RSV infection sets up a process that leads to recurrent wheezing or whether those already predisposed to asthma are more likely to become severely ill with RSV has yet to be determined.
Symptoms of pneumonia in immuno-compromised patients such as in transplant patients and especially bone marrow transplant patients should be evaluated to rule out RSV infection. This can be done by means of PCR testing for RSV nucleic acids in peripheral blood samples if all other infectious processes have been ruled out or if it is highly suspicious for RSV such as a recent exposure to a known source of RSV infection.
, and can remain viable for a half an hour or more on hands or for up to 5 hours on countertops.
However, palivizumab
(brand name Synagis manufactured by MedImmune), a moderately effective prophylactic drug is available for infants at high risk. Palivizumab is a monoclonal antibody directed against RSV surface fusion protein
. It is given by monthly injections, which are begun just prior to the RSV season and are usually continued for five months. RSV prophylaxis is indicated for infants that are premature or have either cardiac or lung disease, but the cost of prevention limits use in many parts of the world. An antiviral drug—Ribavirin
—is licensed for use, but its efficacy is limited.
One study noted a 26% reduction in length of stay: 2.6 ± 1.9 days, compared with 3.5 ± 2.9 days in the untreated group (p=0.05).
Supportive care includes fluids and oxygen until the illness runs its course. Salbutamol
may be used in an attempt to relieve any bronchospasm
if present. Increased airflow, humidified and delivered via nasal cannula
, may be supplied in order to reduce the effort required for respiration. Adrenaline, bronchodilators, steroids, and ribavirin confer "no real benefit".
Virus
A virus is a small infectious agent that can replicate only inside the living cells of organisms. Viruses infect all types of organisms, from animals and plants to bacteria and archaea...
that causes respiratory tract
Respiratory tract
In humans the respiratory tract is the part of the anatomy involved with the process of respiration.The respiratory tract is divided into 3 segments:*Upper respiratory tract: nose and nasal passages, paranasal sinuses, and throat or pharynx...
infections. It is the major cause of lower respiratory tract infection
Lower respiratory tract infection
Lower respiratory tract infection while often used as a synonym for pneumonia, can also be applied to other types of infection including lung abscess and acute bronchitis...
s and hospital visits during infancy and childhood. A prophylactic medication (not a vaccine
Vaccine
A vaccine is a biological preparation that improves immunity to a particular disease. A vaccine typically contains an agent that resembles a disease-causing microorganism, and is often made from weakened or killed forms of the microbe or its toxins...
) exists for preterm birth (under 35 weeks gestation) infants and infants with a congenital heart defect
Congenital heart defect
A congenital heart defect is a defect in the structure of the heart and great vessels which is present at birth. Many types of heart defects exist, most of which either obstruct blood flow in the heart or vessels near it, or cause blood to flow through the heart in an abnormal pattern. Other...
(CHD) or bronchopulmonary dysplasia
Bronchopulmonary dysplasia
Bronchopulmonary dysplasia is a chronic lung disorder that is most common among children who were born prematurely, with low birthweights and who received prolonged mechanical ventilation to treat respiratory distress syndrome...
(BPD). Treatment is limited to supportive care, including oxygen therapy
Oxygen therapy
Oxygen therapy is the administration of oxygen as a medical intervention, which can be for a variety of purposes in both chronic and acute patient care...
.
In temperate climates there is an annual epidemic
Epidemic
In epidemiology, an epidemic , occurs when new cases of a certain disease, in a given human population, and during a given period, substantially exceed what is expected based on recent experience...
during the winter months. In tropical climate
Tropical climate
A tropical climate is a climate of the tropics. In the Köppen climate classification it is a non-arid climate in which all twelve months have mean temperatures above...
s, infection is most common during the rainy season.
In the United States, 60% of infants are infected during their first RSV season, and nearly all children will have been infected with the virus by 2–3 years of age. Of those infected with RSV, 2–3% will develop bronchiolitis
Bronchiolitis
Bronchiolitis is inflammation of the bronchioles, the smallest air passages of the lungs. It usually occurs in children less than two years of age and presents with coughing, wheezing, and shortness of breath. This inflammation is usually caused by viruses...
, necessitating hospitalization. Natural infection with RSV induces protective immunity which wanes over time—possibly more so than other respiratory viral infections—and thus people can be infected multiple times. Sometimes an infant can become symptomatically infected more than once, even within a single RSV season. Severe RSV infections have increasingly been found among elderly patients.
RSV is a negative-sense, single-stranded RNA virus
RNA virus
An RNA virus is a virus that has RNA as its genetic material. This nucleic acid is usually single-stranded RNA but may be double-stranded RNA...
of the family Paramyxoviridae, which includes common respiratory viruses such as those causing measles
Measles
Measles, also known as rubeola or morbilli, is an infection of the respiratory system caused by a virus, specifically a paramyxovirus of the genus Morbillivirus. Morbilliviruses, like other paramyxoviruses, are enveloped, single-stranded, negative-sense RNA viruses...
and mumps
Mumps
Mumps is a viral disease of the human species, caused by the mumps virus. Before the development of vaccination and the introduction of a vaccine, it was a common childhood disease worldwide...
. RSV is a member of the paramyxovirus subfamily Pneumovirinae. Its name comes from the fact that F proteins on the surface of the virus cause the cell membranes on nearby cells to merge, forming syncytia.
Signs and symptoms
For most people, RSV produces only mild symptoms, often indistinguishable from common coldCommon cold
The common cold is a viral infectious disease of the upper respiratory system, caused primarily by rhinoviruses and coronaviruses. Common symptoms include a cough, sore throat, runny nose, and fever...
s and minor illnesses. The Centers for Disease Control consider RSV to be the "most common cause of bronchiolitis (inflammation of the small airways in the lung) and pneumonia
Pneumonia
Pneumonia is an inflammatory condition of the lung—especially affecting the microscopic air sacs —associated with fever, chest symptoms, and a lack of air space on a chest X-ray. Pneumonia is typically caused by an infection but there are a number of other causes...
in children under 1 year of age in the United States".
For some children, RSV can cause bronchiolitis
Bronchiolitis
Bronchiolitis is inflammation of the bronchioles, the smallest air passages of the lungs. It usually occurs in children less than two years of age and presents with coughing, wheezing, and shortness of breath. This inflammation is usually caused by viruses...
, leading to severe respiratory illness requiring hospitalization and, rarely, causing death. This is more likely to occur in patients that are immunocompromised or infants born prematurely
Premature birth
In humans preterm birth refers to the birth of a baby of less than 37 weeks gestational age. The cause for preterm birth is in many situations elusive and unknown; many factors appear to be associated with the development of preterm birth, making the reduction of preterm birth a challenging...
. Other RSV symptoms common among infants include listlessness, poor or diminished appetite, and a possible fever.
Recurrent wheezing and asthma
Asthma
Asthma is the common chronic inflammatory disease of the airways characterized by variable and recurring symptoms, reversible airflow obstruction, and bronchospasm. Symptoms include wheezing, coughing, chest tightness, and shortness of breath...
are more common among individuals who suffered severe RSV infection during the first few months of life than among controls; whether RSV infection sets up a process that leads to recurrent wheezing or whether those already predisposed to asthma are more likely to become severely ill with RSV has yet to be determined.
Symptoms of pneumonia in immuno-compromised patients such as in transplant patients and especially bone marrow transplant patients should be evaluated to rule out RSV infection. This can be done by means of PCR testing for RSV nucleic acids in peripheral blood samples if all other infectious processes have been ruled out or if it is highly suspicious for RSV such as a recent exposure to a known source of RSV infection.
Virology
RSV has 10 genes encoding 11 proteins—there are 2 open reading frames of M2. NS1 and NS2 inhibit type I interferon activity. N encodes nucleocapsid protein that associates with the genomic RNA forming the nucleocapsid. M encodes the Matrix protein required for viral assembly. SH, G and F form the viral coat. The "G" protein is a surface protein that is heavily glycosylated. It functions as the attachment protein. The "F" protein is another important surface protein; F mediates fusion, allowing entry of the virus into the cell cytoplasm and also allowing the formation of syncytia. The "F" protein is homologous in both subtypes of RSV; antibodies directed at the "F" protein are neutralizing. In contrast, the "G" protein differs considerably between the two subtypes. M2 is the second matrix protein also required for transcription, it encodes M2-1 (elongation factor) and M2-2 (transcription regulation), M2 contains CD8 epitopes. L encodes the RNA polymerase. The phosphoprotein P is a cofactor for L. The atomic structure is now available for two of them, N and M. The genome is transcribed sequentially from NS1 to L with reduction in expression levels along its lengthTransmission
RSV spreads easily by direct contactDirect Contact
Direct Contact is a direct-to-DVD film starring Dolph Lundgren. The production company is Nu Image. The movie was filmed in Bulgaria, and stars Swedish actor Dolph Lundgren and Michael Paré...
, and can remain viable for a half an hour or more on hands or for up to 5 hours on countertops.
Prevention
As the virus is ubiquitous in all parts of the world, avoidance of infection is not possible. Epidemiologically, a vaccine would be the best answer. A vaccine trial in 1960s using a formalin-inactivated vaccine (FI-RSV), increased disease severity in children who had been vaccinated. There is much active investigation into the development of a new vaccine, but at present no vaccine exists. Some of the most promising candidates are based on temperature sensitive mutants which have targeted genetic mutations to reduce virulence.However, palivizumab
Palivizumab
Palivizumab is a monoclonal antibody produced by recombinant DNA technology. It is used in the prevention of respiratory syncytial virus infections...
(brand name Synagis manufactured by MedImmune), a moderately effective prophylactic drug is available for infants at high risk. Palivizumab is a monoclonal antibody directed against RSV surface fusion protein
Protein
Proteins are biochemical compounds consisting of one or more polypeptides typically folded into a globular or fibrous form, facilitating a biological function. A polypeptide is a single linear polymer chain of amino acids bonded together by peptide bonds between the carboxyl and amino groups of...
. It is given by monthly injections, which are begun just prior to the RSV season and are usually continued for five months. RSV prophylaxis is indicated for infants that are premature or have either cardiac or lung disease, but the cost of prevention limits use in many parts of the world. An antiviral drug—Ribavirin
Ribavirin
Ribavirin is an anti-viral drug indicated for severe RSV infection , hepatitis C infection and other viral infections. Ribavirin is a prodrug, which when metabolised resembles purine RNA nucleotides...
—is licensed for use, but its efficacy is limited.
Treatment
Studies of nebulized hypertonic saline have shown that the "use of nebulized 3% HS is a safe, inexpensive, and effective treatment for infants hospitalized with moderately severe viral bronchiolitis" where "respiratory syncytial virus (RSV) accounts for the majority of viral bronchiolitis cases".One study noted a 26% reduction in length of stay: 2.6 ± 1.9 days, compared with 3.5 ± 2.9 days in the untreated group (p=0.05).
Supportive care includes fluids and oxygen until the illness runs its course. Salbutamol
Salbutamol
Salbutamol or albuterol is a short-acting β2-adrenergic receptor agonist used for the relief of bronchospasm in conditions such as asthma and chronic obstructive pulmonary disease. It is marketed as Ventolin among other brand names....
may be used in an attempt to relieve any bronchospasm
Bronchospasm
Bronchospasm or a bronchial spasm is a sudden constriction of the muscles in the walls of the bronchioles. It is caused by the release of substances from mast cells or basophils under the influence of anaphylatoxins...
if present. Increased airflow, humidified and delivered via nasal cannula
Nasal cannula
The nasal cannula is a device used to deliver supplemental oxygen or airflow to a patient or person in need of respiratory help. This device consists of a plastic tube which fits behind the ears, and a set of two prongs which are placed in the nostrils. Oxygen flows from these prongs...
, may be supplied in order to reduce the effort required for respiration. Adrenaline, bronchodilators, steroids, and ribavirin confer "no real benefit".
External links
- PreemieCare information and support on premature infants including in-depth resources on RSV and our comprehensive NICU Glossary.
- Synagis (registered to MedImmune, manufacturer of Synagis)
- Virazole (registered to Valeant Pharmaceuticals, manufacturer of Virazole)
- The Family Doctor
- RSV in Infants: Information includes symptoms, treatment, and prevention.
- Biotrin providers of RSV kits
- Control of Communicable Diseases in Man. American Public Health Association.