Human Respiratory syncytial virus (HRSV). Cut-away illustration showing the inner structure and RNA. This orthopneumovirus, a type of paramyxovirus, is a cause of human respiratory tract infections. It consists of RNA (ribonucleic acid) genetic material enclosed in a protein coat, or capsid, within a phospholipid envelope. The envelope is covered in protein spikes, which enable the virus to attach to and enter a host cell. In adults, HRSV only affects the upper respiratory tract, but in infants bronchiolitis (bronchiole inflammation) or bronchopneumonia can result.