Human respiratory syncytial virus

Human respiratory syncytial virus (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.

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RSV causes respiratory tract infections in patients of all ages. It is the major cause of lower respiratory tract infection during infancy and childhood. 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, and nearly all children will have been infected with the virus by 2-3 years of age. Natural infection with RSV does not induce protective immunity, and thus people can be infected multiple times. Sometimes an infant can become symptomatically infected more than once even within a single RSV season. More recently, severe RSV infections have increasingly been found among elderly patients as well.

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 and pneumonia among infants and children under 1 year of age."^[1] 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.[1].

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 is a matter of considerable debate.

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. Unfortunately, vaccine development has been fraught with spectacular failure and with difficult obstacles. Researchers are working on a live, attenuated vaccine, but at present no vaccine exists. 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 proteins. 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.

Treatment

Ribavirin, a broad-spectrum antiviral agent, was once employed as adjunctive therapy for the sickest patients; however, its efficacy has been called into question by multiple studies, and most institutions no longer use it.

Treatment is otherwise supportive care only with fluids and oxygen until the illness runs its course. Amino acid sequences 200-225 and 255-278 of the F protein of human respiratory syncytial virus (HRSV) are T cell epitopes (Bourgeois et al., 1991; Corvaisier et al, 1993). Peptides corresponding to these two regions were synthesized and coupled with keyhole limpet haemocyanin (KLH). The two conjugated proteins were administered intranasally to BALB/c mice alone or together with cholera toxin B (CTB). ELISAs revealed that the mixture of the conjugates with CTB increased not only the systemic response but also the mucosal immune response of the saliva. The systemic response was lower and the mucosal immune response was undetectable in mice immunized with the conjugates on their own. These results suggest that these two peptide sequences are effective epitopes for inducing systemic and mucosal immune responses in conjunction with CTB, and may provide the basis for a nasal peptide vaccine against RSV for human use. [2]

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