Human Respiratory Syncytial Virus: Biology, Epidemiology, and Control

According to the World Health Organization, acute lower respiratory tract infection (ALRI) is the fourth leading cause of death worldwide, responsible for approximately 3.1 million (5.5%) of the 56 million estimated deaths per year. Human respiratory syncytial virus (RSV) is recognized as the most important cause of ALRI in infants worldwide. It is estimated that every year 33.8 million new cases of RSV-related ALRIs occur and cause approximately 200,000 deaths in children younger than 5 years; of note, 99% of these deaths occur in developing countries. Usually primary infections occur during the first 2 years of life and are symptomatic, causing from mild upper respiratory tract illness to severe ALRI, and in some cases pneumonia and bronchiolitis may occur simultaneously. Recurrent infections throughout life are common but normally cause milder upper respiratory tract illness. Several studies also associated severe RSV infections during infancy with permanent lung function reduction in adulthood, with higher risk of asthma. The seasonality of the virus varies but it is often detected throughout the year. In South America the highest incidence occurs in the months of January to June. Despite the clinical importance and the disease burden associated with RSV, there is neither specific treatment nor vaccines widely accepted and available nowadays.