Respiratory Syncytial Virus (RSV) is a clinically important virus and is the leading viral cause of lower respiratory tract infection in infants and also causes severe infections in the elderly. RSV infects approximately 60 million people and is responsible for an estimated 160,000 deaths annually worldwide.

Fluorescently labelling parts of a virus or cell allows researchers to look at them with a high-resolution 'confocal' microscope. This microscope uses lasers to illuminate the fluorescent markers and can be tuned to detect different colours. This is a powerful way of examining how viruses behave in infected cells.