Disease
Respiratory Syncytial Virus (RSV)
Author
Ben Kaufman, Biol 230, Spring 2009
Causative Agents
RSV is a single-stranded, negative-sense RNA virus containing 2 non-structural and 8 structural proteins. It is enveloped, ranging in size from 100-350 nm. RSV is spherical or pleomorphic (def) in shape. It belongs to the order Mononegavriales, the Paramyxoviridae family, and the genus Pneumovirus. [2]
Epidemiology
Worldwide, RSV infects about 64 million and kills 160,000 per year. RSV is the leading cause of bronchiolitis (def) and pneumonia in infants, and is the leading cause of viral deaths in infants. [7] Almost all children are infected at least once by age 2. Only 25% to 40% of children have respiratory signs and symptoms, and 0.5% to 2% require hospitalization. Most who are hospitalized are under 6 months of age. Approximately 75,000 to 125,000 infants are hospitalized each year in the United States, and these peak seasonally (fall through spring). After infection, individuals do not develop complete immunity from future infections. Therefore, the same individual may become infected with RSV more than once, even within the same season. [1]
While it is not clear exactly how RSV makes an initial attachment to host cells, RSV glycoprotein G has a structural homology with fractalin (chemokine (def) CX3CL1). This chemokine could be important for the adsorption of RSV, and it is found on mast and neuronal cells. Also, RSV glycoprotein F may bind to Toll-like receptor 4 (TLR4) (def), which is especially present in the epithelial cells of the airway and play an important role in innate immunity of RSV. [8]
Transmission
RSV is transmitted via both direct and indirect contact with secretions from the nose and mouth of those infected. RSV is very contagious, predominantly because it can live outside the body on hard surfaces for up to six hours, and is spread easily throughout daycare centers and classrooms. Those infected with RSV are contagious for approximately 3 to 8 days, however some infants and immunosuppressed patients can spread the disease for up to 4 weeks. [4] While reinfection is common, RSV is not capable of latency. [8]
Signs and Symptoms
RSV causes an intense inflammatory response characterized by infiltrates within the small airways, sloughing of epithelial cell, and mucous production. Mucous plugging leads to lower airway obstruction, hyperinflation, and atelectasis (def). Hypoxia and respiratory failure may develop in severe cases. This local immune response and the inflammatory cascade within the airways are critical to the severity of the infection. [8]
The RSV incubation period is 4-6 days. RSV usually causes a mild infection of the upper respiratory tract, sometimes with fever. In children who develop lower respiratory infections such as bronchiolitis or pneumonia, symptoms may include rapid breathing, fever, increased work of breathing as evidenced by accessory muscle use, coughing, wheezing (def), sneezing, decreased activity, decreased appetite, and apnea (def). [4]
Infected healthy adults may develop upper respiratory symptoms including cough, sore throat, headache, fatigue, and fever. Immunocompromised adults may develop lower respiratory infections requiring medical intervention. [1]
Prevention and Treatment
As with most diseases, prevention is the best way to avoid infection. Surface cleaning with disinfectants, frequent and thorough handwashing, and general avoidance of those who are ill, especially their mucosal secretions, can help stop the spread of RSV infection. One should avoid kissing the face and hands of those infected, and should avoid sharing utensils or drinking cups. When coughing or sneezing, one should cover the mouth and nose. [1]
While there is no vaccine available for RSV, there is a drug that may be given prophylactically to those considered at high-risk for infection. Palivizumab (“pah-lih-VIH-zu-mahb”, brand name Synagis) is effective in reducing hospitalizations from RSV infection, and is given via injection monthly throughout the RSV season. Palivizumab is a monoclonal antibody that targets the fusion protein of RSV, preventing infection by inhibiting entry of the genome into the host cell. [9]
For children, especially those born prematurely, current recommendations regarding who should receive Palivizumab are available from the American Academy of Pediatrics [5]. A recent study suggests that RSV incidence and morbidity is high among all children, and that targeting only high-risk children for prophylaxis will have little effect on limiting the prevalence of RSV [6]. Adults who should be considered for prophylaxis include those with chronic heart or lung disease, those with compromised immune systems, and those over the age of 65, especially those living in long-term care facilities. It is important to note that Palivizumab can help prevent development of serious RSV infection in the high-risk patient, but it will not treat or cure those already infected, and it will not prevent the spread of the disease. [3]
Treatment for RSV infection is supportive. Fluid replacement, oxygen, acetaminophen for fever, nose blowing, and bulb syringe suctioning will help patients feel better until they recover. Beta agonists (def) may be used to relieve bronchiole constriction, and intubation (def) may be required for ventilatory support. [2, 1]
Bibliography
1. CDC. Respiratory syncytial virus infection. Infection and incidence. 2008. Retrieved April 19, 2009. http://www.cdc.gov/rsv/about/infection.html
2. Wikipedia. Human respiratory syncutial virus. 2009. Retrieved April 19, 2009.
http://en.wikipedia.org/wiki/Respiratory_syncytial_virus
3. CDC. Respiratory syncytial virus infection. Prophylaxis and high-risk groups. 2008. Retrieved April 19, 2009. http://www.cdc.gov/rsv/clinical/prophylaxis.html
4. National Institure of Allergy and Infection Diseases. Respiratory syncytial virus. 2008. Retrieved April 19, 2009. http://www3.niaid.nih.gov/topics/rsv/
5. Pickering LK, Baker CJ, Long SS, McMillan JA, eds. Red Book. 2006 report of the Committee on Infectious Diseases. 27th ed. Elk Grove Village, IL: American Academy of Pediatrics, 2006:560-6.
6. Hall, C. B. et al. The burden of respiratory syncytial virus infection in young children. New England Journal of Medicine, 2009. 360; 6, p588-598.
7. Robinson, R. F. Impact of respiratory syncytial virus in the United States. American Journal of Health-System Pharmacy. 2008. 68; 23, pS3-S6.
8. Smyth, R. L. Innate immunity in respiratory syncytial virus bronchiolitis. Experimental Lung Research, 2007. 33, p543-547.
9. Wikipedia. Palivizumab. 2008. Retrieved April 19, 2009.
http://en.wikipedia.org/wiki/Palivizumab