Friday, September 28, 2018

The Spread of Influenza

Influenza causes substantial disease burden worldwide. An estimated 10%-20% of the world’s population is affected each year by seasonal epidemic influenza. Pandemics arise through antigenic shifts resulting in a new virus that is not related to previous human seasonal influenza viruses.

The spread of bird flu across Asia and parts of Europe and the Middle East, as well as the occasional infections of humans with disconcertingly high number of deaths, have cause concern about potential new global epidemic of influenza.

There is limited scientific evidence on important aspects of disease transmission and on the effectiveness of different strategies to limit transmission.

Influenza or simply “flu” is caused by a virus. It occurs not only in occasional major pandemic outbreaks but also in epidemics or variable severity almost every winter. Influenza replicates in epithelial cells throughout the respiratory tree (both upper and lower tracts). Human viruses preferentially bind to cell surface receptors terminating in an α(2,6)-linkage in contrast to avian viruses which prefer an α(2,3)-linkage.

The term “influenza” has been derived from the Italian influential in the mid 1300s, indicating that, at the time, the illness was believed to result from astrological influences. Yet, the aetiology of the disease and the explanation for its peculiar behaviors remained elusive.

Influenza is thought to spread by droplet, contact and airborne routes. However, the relative likelihood of spread due to each of these modes is not well understood. Respiratory droplets are currently thought to be the main mode of transmission.

There is also some suggestion that influenza may spread through airborne aerosols that are expelled through coughing or sneezing or aerosol generating procedures such as bronchoscopy or intubation.
The Spread of Influenza
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