Forecasting Pandemics

Stephen DeAngelis

March 20, 2008

Resilience is normally defined as the ability to bounce back after some catastrophic event. Needless to say, resilience is a great characteristic for any system to have. Even better than resilience, however, is prevention. Anyone who has ever been sick and recovered agrees that prevention is better than cure. Just as importantly, prevention is cheaper than cure. Companies and healthcare providers are slowly getting on board with that notion; primarily because of the rising costs of health insurance. Prevention of deadly epidemics is exactly what a virologist at UCLA has in mind with a new computer network and prediction model he is championing [“And now here is the virus forecast,” The Economist, 23 February 2008 print edition]. The article begins with news that an experimental treatment for AIDS has failed field tests and that the disease continues to spread.

“AIDS kills over 2m people a year. A way of stopping it spreading is urgently required. Yet according to Nathan Wolfe, a virologist at the University of California, Los Angeles, things need never have got this bad. If there had been, in the 1970s, a programme searching for unrecognised diseases in Africa then AIDS would have been noticed long before so many people had started dying from it. Microbicides and other interventions could have been tested when only hundreds of thousands were infected, rather than tens of millions. AIDS would still have been horrible, but not nearly as horrible as it has become. To try to stop this happening again, Dr Wolfe is attempting to create what he calls the Global Viral Forecasting Initiative (GVFI). This is still a pilot project, with only half a dozen sites in Africa and Asia. But he hopes, if he can raise the $50m he needs, to build it into a planet-wide network that can forecast epidemics before they happen, and thus let people prepare their defences well in advance.”

Forecasting the spread of known diseases, like the flu, is relatively easy compared to what Dr. Wolfe is attempting to do. He wants to create a system that will forecast the spread of heretofore unknown diseases.

“Dr Wolfe outlined his ideas, and the research that has led him to believe they are feasible, to this year’s meeting of the American Association for the Advancement of Science (AAAS) in Boston. He began his work nearly a decade ago in Cameroon, in a project reminiscent of the 19th-century animal-collecting expeditions that pushed into the forest to look for new species. Except that his quarry is viruses, not butterflies and birds.”

These are not “free range” viruses. They are not simply lying about on the jungle floor waiting to be discovered. They hide in animal species.

“Almost all human viruses whose origins are known have come from animals. But it is not simply a matter of an animal virus suddenly finding humans to be a congenial host, and flourishing as a result. With AIDS, for example, the global epidemic is caused by what was originally a chimpanzee virus. There is, however, a second form of AIDS, caused by a monkey virus. This has not become global. It is pretty much restricted to West Africa. Moreover, there are a further two very rare forms caused by different versions of the chimpanzee virus. These rare forms are examples of what Dr Wolfe calls viral chatter, a term borrowed from intelligence agencies which monitor telephones for the use of certain words or unusual patterns of communication.”

Pattern recognition is useful in a lot areas of human endeavor. Healthcare may be foremost among the areas where it can pay big, early dividends.

“[Dr. Wolfe’s] thesis is that there is continual low-level interchange of viruses between species. That is particularly so for people, such as hunters and farmers, who are in constant and often bloody proximity to animals. His hope is that by monitoring this viral chatter he will be able to spot pathogens before they take the second, crucial evolutionary step of being able to transmit themselves from one human to another. So far, he has concentrated his efforts on a group known as retroviruses, of which HIV is one. He has already found three examples of ‘foamy viruses’ jumping from wild apes and monkeys to Cameroonian hunters. At the moment, no known foamy virus can spread between people. But until the 20th century that was true of the simian equivalents of HIV. He has also found two new members of a group called HTLV that have moved from monkeys to men. Since HTLV-1, an example of the group discovered several decades ago, has already spread around the world, these cases are particularly noteworthy. HTLV-1 is not as common as HIV, and causes symptoms in only 5-10% of those it infects. But those symptoms can include a fatal leukaemia. And a different type of HTLV might not be so choosy about whom it kills. Even more worryingly, Dr Wolfe has found many examples of viruses recombining in his Cameroonian hunters. Recombined viruses often have properties present in neither parent. Sometimes these include the ability to jump from human to human. The pandemic version of HIV is the result of such a recombination.”

Dr. Wolfe wants the touchstone of his initiative to be the most complete catalog of viruses possible. That is why he goes virus hunting and he wants others to join in the search. He believes his greatest allies in this effort will not be other scientists, but native hunters.

“The next stage of the project is to try to gather as complete an inventory as possible of animal viruses, and Dr Wolfe has enlisted his hunters to take blood samples from whatever they catch. He is collaborating with Eric Delwart and Joe DeRisi of the University of California, San Francisco, to screen this blood for unknown viral genes that indicate new species. The GVFI will also look at people, monitoring symptoms of ill health of unknown cause and trying to match these with unusual viruses.”

If Dr. Wolfe can raise the money he is seeking, the next step will be to enlist animal stall merchants in Asian countries to join his cadre of hunters.

“Animal markets are next in line. Dr Wolfe is working with Peter Daszak, of the Consortium for Conservation Medicine, to study the so-called wet markets of China where SARS began in 2002. They will inspect the animals sold in them, and test the stallholders and customers for signs of dodgy viruses. Dr Daszak is a co-author of a study published in this week’s Nature that maps the global ‘hot spots’ of emerging diseases and concludes, as Dr Wolfe has, that the real threat lies in the tropics. That is despite the fact that most new diseases are (as with AIDS) first noticed in rich countries.”

The assertion that new diseases are “first noticed” in rich countries is a bit patronizing. Those who contract diseases in poor countries (and their loved ones) certainly notice them. The difference is that they are not empowered to do anything about it. Even healthcare workers in poor countries who “notice” new diseases have few tools with which to work. A concomitant benefit of Dr. Wolfe’s initiative is that these diseases would finally be noticed in time to hel
p those least capable of helping themselves. The payoff for those living in rich countries is that they may never have to face the threat such diseases pose. The article concludes:

“If and when the GVFI is running smoothly, Dr Wolfe hopes to see not only what is threatening, but also to identify the general characteristics (if any) that threatening viruses share. If some features are regularly associated with a propensity to become pandemic, then forecasting outbreaks of new viral diseases will become easier and more scientific. At that point, this branch of medicine will be able to make the most important leap of all—from cure to prevention. And then a catastrophe like AIDS will need never happen again.”

I doubt we have seen the last pandemic, but even preventing one could save millions of lives. Technology is a marvelous thing in the hands of someone who knows how to stretch the envelope of the possible. I suspect we haven’t heard the last of Dr. Wolfe and his pandemic prediction scheme.