Chapter 25 Respiratory tract viruses

Respiratory tract infections are among the commonest of illnesses, and most individuals will experience two to five infections during each year of their lives. The illnesses vary from relatively mild common colds caused by rhinoviruses and coronaviruses, to severe bronchiolitis and pneumonia caused by adenoviruses and influenza viruses and respiratory syncytial virus (RSV) in infants: the former is associated with little morbidity and no mortality, while influenza is responsible annually for between 1 and 25 thousand deaths per 50 million population. Over 140 viruses cause respiratory tract infections, with the added complications of influenza viruses where new antigenic variants are recognized almost annually; and immunity to infection by one virus strain offers little or no protection to infection by others. Knowledge of the mechanisms of spread of respiratory viruses is largely understood and has helped in infection control; however, the clinical signs and symptoms of infection tend not to be diagnostic of the causative agent; and although vaccines have been developed for the more serious infections such as influenza and some adenovirus infection, none are available for other important infections. Treatment is largely symptomatic, but the compounds ribovirin for RSV infection and amantadine for influenza virus infection have been shown to be effective. Much remains to be discovered before more effective measures can be implemented to limit the enormous costs incurred by these infections. The number of viruses involved is large, and the spectrum of illness complex: in the present chapter, the viruses are described, together with the features of the epidemiology, pathogenesis, clinical disease, and treatment.