Flu virus migration
Excerpts from ABC Health Report with Dr Norman Swan
Dr Colin Russell, who's Head of Epidemiology at the Centre for Pathogen Evolution at the University of Cambridge in the UK
...Colin Russell: The WHO global influenza surveillance network collects influenza viruses from over 100 countries around the world and one of the questions has been how do influenza viruses migrate around the world. So in collaboration with the WHO global influenza surveillance network we looked at all of the data that was collected between 2002 and 2007.
Norman Swan: In a real time sense?
Colin Russell: Yes, the data is collected in real time and it gives us an opportunity to watch virus evolution occur. So viruses are collected and the data is assimilated into reports every six months to judge which viruses should go into the vaccine for the upcoming influenza season. So this decision is made twice per year, once for the northern hemisphere and once for the southern hemisphere...
...Norman Swan: So spontaneous combustion in local areas?
Colin Russell: Well sort of something like that you know it passes at some low level from individual to individual between epidemics and then it really takes off when everyone is immuno-compromised because it's so cold outside for example. And then yet another hypothesis is that maybe influenza viruses came out of China but there had not previously been enough evidence to know which one of those hypotheses was correct.
Norman Swan: So what did you do?
Colin Russell: In collaboration with the WHO global influenza surveillance network we looked at all of the data collected from 2002 to 2007 so this was about 13,000 influenza viruses from around the world and using a combination of genetic analyses looking at the DNA code of these viruses and antigenic analysis actually looking at the proteins on the surface of the virus.
Norman Swan: Those are the proteins to which the immune system reacts?
Colin Russell: Yes exactly, so these are the haemaglutinin protein. We were able to determine that influenza viruses come from east and south-east Asia as a region, not just China but the entire region into the rest of the world each year. And this was big because the other thing that we were able to show was that influenza viruses don't persist locally in between epidemics. And it's not that they're coming out of the tropics each year, and they're not bouncing back and forth between the northern and southern hemispheres but rather they literally come from Asia each and every year...
...Colin Russell: Exactly, so this is one of the hypotheses that you're getting at here that viruses migrate back and forth between the northern and southern hemispheres because of the differences in the timing of the seasons.
Norman Swan: And you're saying that doesn't happen?
Colin Russell: No. One of the things that we see is that viruses migrate out of east and south east Asia all of the time, presumably they are being carried by unwitting passengers on civil transport and they get taken to Australia and New Zealand and North America and to Europe and this happens all of the time. So we see viruses isolated year round in any place where surveillance is really strong but one of the things that we showed in looking at all of this global data was that viruses that you see in between epidemics in temperate regions of the world aren't related to viruses in the previous epidemic...
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