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Human respiratory syncytial virus
Transmission electron micrograph of RSV
Virus classification
Group: Group V ((-)ssRNA)
Order: Mononegavirales
Family: Paramyxoviridae
Human respiratory syncytial virus
Classification and external resources
ICD-10 B97.4
ICD-9 079.6
DiseasesDB 11387
MedlinePlus 001564
eMedicine ped/2706
MeSH D018357

Human respiratory syncytial virus (RSV) is a virus that causes respiratory tract infections. It is the major cause of lower respiratory tract infection and hospital visits during infancy and childhood. There is no vaccine. Treatment is limited to supportive care, including oxygen.

In temperate climates there is an annual epidemic during the winter months. In tropical climates, infection is most common during the rainy season.

In the United States, 60% of infants are infected during their first RSV season[1], and nearly all children will have been infected with the virus by 2–3 years of age[1]. Of those infected with RSV, 2–3% will develop bronchiolitis necessitating hospitalization [2]. 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.

Contents

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 F (fusion) and G (glycoproteins) are required for viral entry into cells and also determine the antibody response. 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 [3] and M [4]. The genome is transcribed sequentially from NS1 to L with reduction in expression levels along its length

Presentation

For most people, RSV produces only mild symptoms, often indistinguishable from common colds 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".[5] 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.[6]

Recurrent wheezing and asthma are more common among individuals who suffered severe RSV infection during the first few months of life than among controls;[7] 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.

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.[8] 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 (brand name Synagis), 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.[9]

Treatment

Treating respiratory syncytial virus bronchiolitis "remains a good example of therapeutic nihilism—nothing works except oxygen". Adrenaline, bronchodilators, steroids, and ribavirin confer "no real benefit".[10]

Treatment is supportive care only, with fluids and oxygen until the illness runs its course. Albuterol 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.

Recent studies with 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".[11]

See also

References

  1. ^ a b Glezen WP, Taber LH, Frank AL, Kasel JA (1986). "Risk of primary infection and reinfection with respiratory syncytial virus". Am. J. Dis. Child. 140 (6): 543–6. PMID 3706232. 
  2. ^ Hall CB, Weinberg GA, Iwane MK, Blumkin AK, Edwards KM, Staat MA, Auinger P, Griffin MR, Poehling KA, Erdman D, Grijalva CG, Zhu Y, Szilagyi P. (2009). "The burden of respiratory syncytial virus infection in young children.". N Engl J Med. 360 (6): 588–98. PMID 19196675. 
  3. ^ R. G. Tawar, S. Duquerroy, C Vonrhein, P. F. Varela, L. Damier-Piolle, N. Castagne, K. McLellan, H. Bedouelle, G. Bricogne, D. Bhella, J.-F. Eleouet, F. A. Rey Crystal Structure of a Nucleocapsid-like Nucleoprotein-RNA Complex of Respiratory Syncytial Virus Science, Volume 326, Pages 1279-1283.e1
  4. ^ V. A. Money, H. K. McPhee, J. A. Mosely, J. M. Sanderson, R. P. Yeo Surface features of a Mononegavirales matrix protein indicate sites of membrane interaction. Proc Natl Acad Sci U S A. 106, Pages 4441-4446.e1
  5. ^ "Respiratory Syncytial Virus". CDC, Respiratory and Enteric Viruses Branch. Reviewed on October 17, 2008. http://www.cdc.gov/rsv/index.html. Retrieved 2009-02-10. 
  6. ^ "RSV in Infants — LoveToKnow Baby". baby.lovetoknow.com. http://baby.lovetoknow.com/wiki/RSV_in_Infants. Retrieved 2010-01-26. 
  7. ^ ajrccm.atsjournals.org Evidence of a Causal Role of Winter Virus Infection during Infancy in Early Childhood Asthma-Am. J. of Respiratory and Critical Care Med. Vol 178. pp. 1123–1129
  8. ^ Kim, H. W., J. G. Canchola, C. D. Brandt, G. Pyles, R. M. Chanock, K. Jensen, and R. H. Parrott. (1969). "Respiratory syncytial virus disease in infants despite prior administration of antigenic inactivated vaccine.". Am.J.Epidemiol. 89: 422–434. PMID 4305198. 
  9. ^ Ventre, K. and A. G. Randolph (2007). "Ribavirin for respiratory syncytial virus infection of the lower respiratory tract in infants and young children.". Cochrane.Database.Syst.Rev CD000181. PMID 17253446. 
  10. ^ Jenny Handforth, Mike Sharland, Jon S Friedland. Editorial: Prevention of respiratory syncytial virus infection in infants. BMJ 2004;328:1026–1027 (1 May), doi:10.1136/bmj.328.7447.1026
  11. ^ B. Kuzik, S. Al Qadhi, S. Kent, M. Flavin, W. Hopman, S. Hotte, S. Gander Nebulized Hypertonic Saline in the Treatment of Viral Bronchiolitis in Infants The Journal of Pediatrics, Volume 151, Issue 3, Pages 266-270.e1

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.
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