Illustration of a cross-section through a human respiratory syncytial virus (hRSV) particle landing on the surface of a human respiratory endothelial cell. At the core is a single-stranded RNA (ribonucleic acid) genome (bright pink), which is capped by large (L) proteins (purple). Surrounding the core are the M1 and M2 matrix proteins (purple) and a lipid bilayer envelope (grey). Within the envelope are F (globular) and G (string-like) glycoproteins that play a role in the attachment (G) and fusion (F) of the virus with a host cell. RSV is a pneumovirus, a type of paramyxovirus. It is a major cause of respiratory tract infections in humans, and is the most common cause of bronchiolitis and pneumonia among infants.