Influenza and emerging viruses

Is influenza the model that could help us tackle emerging viruses?

by David Bradley

at the Royal Society

Despite intense investigation and the development of vaccine, influenza virus remains a major threat to public health, said Professor Robin Bush of the University of California, Irvine. But, do influenza's lessons apply to SARS?

Influenza and SARS are both RNA viruses with many similarities and many major differences. But, the emergence of new strains of influenza throughout human history can help us understand SARS.

Killer strains of influenza type A are thought to begin in the intestines of waterfowl, such as ducks. The intestine harbours the viral components that, under the right conditions, allow the virus to jump to another species, such as a chicken, and then to people. The leap from symptom-free ducks to the Spanish influenza epidemic of 1918 remains a mystery. Where exactly did this killer come from and why did it become so virulent?

Research on genetic material extracted from frozen samples has taken us tantalizingly close to an answer. We have no genetic records of the strains just prior to their emergence in people so stepping back to the source is currently impossible. We must answer why these viruses that have infected only birds for decades suddenly become infectious to humans and why is such emergence quite rare? Bush suggested that if we continue to keep company with our animals and provide them with over-crowded living conditions then the frequency of emerging epidemics will inevitably increase.

Clues may lie in the places where these viruses appear to originate - the farms and markets of Southeast Asia, for instance. We must understand the factors involved in an emerging virus appearing and learn the lessons of diseases such as influenza if we hope to come quickly to grips with SARS and its ilk.

Read more in Session 2: SARS - a new disease