The Spread of Influenza and Other Respiratory Viruses: Complexities and Conjectures

Since ancient times, the abrupt appearance and spread of maladies has demanded and defied explanation by mankind. In 400 b.c., Hippocrates suggested that the environment, including water and air, were important, and in the second century a.d., Galen suggested that outbreaks of illnesses were caused by inhaled air. For centuries thereafter, the prime theories proposed that illnesses arose from mystical influences and noxious effluvia borne by air [1]. The widespread devastation inflicted by plagues was thought to result from inhaling the putrescent vapors of decaying corpses. This belief in “miasmas” (derived from the Greek word for pollution) engendered perhaps the first infection-control procedures. The unfortunate souls assigned to handle the corpses were gowned in long robes with hoods to which were attached beaks stuffed with herbs, which were intended to filter the miasmas from the air (figure 1). Epidemics of influenza were similarly believed to erupt from the dispersion of mystical elements. Indeed, our current term