Respiratory syncytial virus (RSV) is a major cause of respiratory illness in young children. RSV infection produces a variety of signs and symptoms involving different areas of the respiratory tract, from the nose to the lungs. RSV is a negative sense, enveloped RNA virus. The virion is variable in shape and size with average diameter of between 120 and 300 nm. Its genome consists of single stranded, negative sense RNA that encodes three envelope glycoproteins, a small hydrophobic (SH) protein of unknown function, a major glycoprotein (G) known as the attachment protein, and a fusion (F) protein.