Materiali e files

Abstract e references.

ABSTRACT: Seasonal cycles of infectious diseases have been variously attributed to
changes in atmospheric conditions, the prevalence or virulence of the pathogen,
or the behavior of the host. Some observations about seasonality are difficult to
reconcile with these explanations. These include the simultaneous appearance
of outbreaks across widespread geographic regions of the same latitude; the
detection of pathogens in the off-season without epidemic spread; and the
consistency of seasonal changes, despite wide variations in weather and human
behavior. In contrast, an increase in susceptibility of the host population,
perhaps linked to the annual light/dark cycle and mediated by the pattern of
melatonin secretion, might account for many heretofore unexplained features of
infectious disease seasonality. Ample evidence indicates that photoperioddriven
physiologic changes are typical in mammalian species, including some in
humans. If such physiologic changes underlie human resistance to infectious
diseases for large portions of the year and the changes can be identified and
modified, the therapeutic and preventive implications may be considerable.