Bronchitis and Bronchiolitis caused by viruses and bacteria. Bronchitis causes inflammation of an upper respiratory tract infection by viral agents such as influenza, rubeola, rubella, pertussis, herpes simplex virus, rhinovirus, scarlet fever and typhoid fever, H influenzae and S pneumoniae. Bronchiolitis is a viral respiratory disease or inflammation of the bronchial tree and it is primarily caused by respiratory syncytial virus. Other viruses, including parainfluenza viruses, influenza viruses and adenoviruses (as well as occasionally M pneumoniae) are also known to cause bronchiolitis.