**1. Introduction**

Human respiratory syncytial virus (RSV), despite being a human virus, was first isolated in 1955 from a chimpanzee with respiratory illness [1]. Since its first discovery, it did not take long to isolate RSV from infants with respiratory diseases. Indeed, serological studies verified the existence of RSV infection in infants and children [2, 3]. Now, RSV infection is a prominent cause of lower respiratory tract diseases (bronchiolitis and pneumonia) and hospitalization in children worldwide [4]. According to the most recent virus taxonomy, RSV now belongs to a new family *Pneumoviridae* of the order *Mononegavirales* [5].
