Respiratory Syncytial Virus A (RSV A). Scanning electron micrograph (SEM) of a HEp2/HeLa cell (Human epithelial cell) infected with RSV A (Strain Long) showing long filamentous enveloped particles (orange) emerging from the plasma membrane. Respiratory syncytial virus is a common respiratory virus that usually causes mild, cold-like symptoms. Most people recover in a week or two, but RSV can be serious. Infants and older adults are more likely to develop bronchiolitis and pneumonia requiring hospitalization. Magnification: x3200 when printed 10 centimetres wide. Specimen courtesy of Virology Research Services Ltd (Scott Lawrence).