Today's date:
Summer 2009

Preventing the Next Pandemic

Nathan Wolfe, perhaps the world's leading "viral sleuth," is director of the Global Viral Forecasting Initiative and professor of biology at Stanford University. He spoke NPQ in April when the swine flu outbreak was at its height.

NPQ | What are the common types of conditions in which cross-species epidemics or pandemics such as HIV, Ebola, avian flu and now swine flu emerge and incubate? What conditions combine to create a viral hot spot?

Nathan Wolfe | The prevalent conditions for outbreaks in "hotspots" such as the Congo Basin in Central Africa or parts of Southeast Asia are a diversity of wildlife and a density of human population in close interface with domestic animals. The infectious diseases that humanity faces today, by and large, have animal origins.

Humans and animals have been in contact for all known time, of course. People have been hunting for the past 5 million years of human history.

What has changed is the intensified connectivity among humans—planes, trains, automobiles and also, to a certain extent, the movement of animals. Humans are the fuel of these viruses. They need humans to really take off.

If someone living in a sparse rural zone or small village were infected, the virus would move quickly through the small population. Those infected would either die or become immune. That has all changed with accelerated connectivity, especially in our time with globalization. Instead of dying out, diseases now spread and mutate through large populations across vast distances, as HIV and SARS did and now H1N1 (swine flu) has done.

NPQ | In Veracruz, Mexico, the villagers lived near a massive pig farm, downwind and downstream, and could have imbibed viruses from pig waste, from the water, air or borne by birds. Is this the type of interface between animals and humans that could have generated the H1N1 virus?

Wolfe | Some background first. All influenza viruses are bird viruses.

The diversity of birds is much greater than the limited diversity of mammals. There is a lot of potential for back and forth. Within that diversity of birds, viruses can go from wild bird to domestic chickens, then from chickens into pigs, from domestic or wild birds into pigs, from pigs to humans and humans to pigs.

As this back and forth goes on, "daughter viruses" can be formed that are mosaics, little bits from different hosts. Cosmopolitan viruses are created that could be a mishmash, for example, of bird and pig and human. This appears to be the case with H1N1.

Now, a young boy in Mexico, Edgar Hernandez, was said to be "case zero."

But he is not the first case, only the first confirmed case. He is definitely not the individual who was originally infected. The current working hypothesis about H1N1 is that it is a pig virus that entered into humans. But certainly it did not enter through Edgar.

From what we know about viruses like this one, once it is in mammals, it is a respiratory virus. That means you cannot contract it by contact with meat or feces. You can only initially get it by contact with an infected, breathing pig—in other words respiratory aerosols from the breath of that pig. My suspicion, therefore, is that the idea of downstream or downwind contamination from the pig farm is a red herring.

NPQ | How to prevent such pandemics in the future?

Wolfe | While we absolutely need these fire brigade types of responses we are witnessing now to H1N1 in Mexico and elsewhere, it would be much better for public health to prevent outbreaks in the future by closely monitoring or surveilling those hot zones where people have a lot of exposure to animals—the portal of infectious diseases. In this way we could catch any virus upstream before it has a chance to enter the human population

In Cameroon, where my team has studied hunters who are exposed to the body fluids and blood of monkeys, wild pigs and other animals, we were able to discover and map the genes of a novel retrovirus that jumped to humans from gorillas. Because we now have the necessary biological information, we can respond to this disease as soon as it might appear in the broader population with a vaccine or other treatment.

In the area of infectious diseases, we need to do what has been done for heart attacks in medicine over the past few decades—move from treatment after the fact to prediction and prevention.