IOWA CITY —
This is one of the major challenges of working with emerging infectious diseases. As an epidemiologist, the most important thing I try to do is prevent disease — it's much easier to keep that genie corked than to get it back in the bottle. However, with diseases that jump between animals and people — "zoonotic" diseases — we usually don't find that they've moved into the human population until they make someone sick enough to see a doctor. By that time, it may be too late; the microbe may have already become established in the population, adapting to humans stealthily before we were even aware of it. This is probably what happened with the novel H1N1 influenza, and what scientists fear may be happening with other germs all over the world.
It probably seems that there are more unknowns than known quantities with avian influenza viruses. This is not far from the truth. But what we do know without a doubt is that avian influenza viruses will keep jumping species barriers — to humans, to pigs, to other mammals. Some of these may be deadly, ongoing spillover events, like H5N1's repeated reappearance in the human population. Some may be seemingly one-time events, like the avian H7N7 virus that caused a large outbreak of conjunctivitis and one fatality in the Netherlands in 2003. It remains to be seen how the current H7N9 outbreak will play out, but one thing is certain: This won't be the last novel avian influenza virus to infect humans.