Orthomyxoviruses

Excerpt

The orthomyxoviruses (influenza viruses) constitute the genus Orthomyxovirus, which consists of three types (species): A, B, and C. These viruses cause influenza, an acute respiratory disease with prominent systemic symptoms. Pneumonia may develop as a complication and may be fatal, particularly in elderly persons with underlying chronic disease. Type A viruses cause periodic worldwide epidemics (pandemics); both types A and B cause recurring regional and local epidemics. Influenza epidemics have been recorded throughout history. In temperate climates, the epidemics typically occur in the winter and cause considerable morbidity in all age groups. An epidemic with associated mortality has occurred in most of the past 100 years. The worst of these was the 1918 pandemic, which caused about 20 million deaths worldwide and about 500,000 deaths in the United States.