SARS will be eradicated

David Baltimore

We in the U.S. are lucky: somehow we have so far dodged the bullet of SARS. If an infected traveler from China had come here and silently initiated a chain of infection, we could have had the problem that faced Canada. As it is, we can safely go about our lives with much less danger from SARS than we face daily in our automobiles.

It is ironic that Americans and, even more, Europeans, worry about genetically engineered plants and animals, but it is the natural organisms from the wild that pose the greatest threat. We plan for a biowarfare attack, but our preparations serve us best to counter dangers that are a part of the normal microbial world. If it sounds like we are misjudging our enemies, that is a possibility worth pondering.

We still have no idea where SARS came from. It seems pretty clear that it is due to a member of the family of coronaviruses. Somewhere in nature, there must be a species that passes the SARS virus around, just as we pass around the common cold viruses among ourselves. We may never identify that species because such a virus generally causes mild symptoms. Imagine looking for a sneezing squirrel or a diarrheic rabbit. Actually, you needn’t spot the virus while it is spreading in its home population because an infection leaves telltale antibodies in the blood that can be assayed. Also, SARS virus may well be a recombinant, an agent created by joining parts of the genetic material of two different viruses, say, one from a bird and one from a mouse.

The spread of a virus from animal to humans is not a rare occurrence. One estimate I have seen is that it happens on average once a year. But when a virus is adapted to one species, it generally is transmitted poorly in a second species and even if it jumps across, it usually burns itself out. Ebola is such a virus that jumps frequently in Africa. It is daunting to realize that although we have known about Ebola for decades, we still do not know what species harbors it naturally.

The best-known virus to jump species and then be passed around is HIV, the virus that causes AIDS. It seems to have come from chimpanzees, where it causes no known disease. It is actually not transmitted all that efficiently in humans but we help by injecting ourselves or having unprotected sex. It is particularly diabolical because the initial symptoms of an HIV infection are mild and it generally takes years before the immunodeficiency becomes evident. Thus, the virus was able to take hold in the human population before we could establish barriers to its spread. Also, the unwillingness of officials in many countries to face up to the routes of transmission and counsel the population to take precautions allowed it to gain a foothold around the world.

Will SARS end up endemic, like HIV, or sporadic, like Ebola? I believe that we still have a chance to put the genie back in the box. In Vietnam, they seem to have eradicated it. Likewise in Canada. The real problems are China, Hong Kong, and, recently, Taiwan. Hong Kong and Taiwan are small enough that I believe they can eradicate the virus, particularly if they can keep themselves isolated from mainland China. In China, the problem seems much worse because they allowed so much spread before they began serious countermeasures. But the virus is not easily transmitted: it is generally very close contacts who get infected. So there is a chance, even for China. In fact, if China does not want to end up isolated from the rest of the world, it must eradicate the virus.

My confident predictions assume that the virus will not fundamentally change by mutation—or perhaps recombine with a human coronavirus—and find a more effective route of transmission. This is not a common occurrence when a virus jumps species, so it is not something to expect, but it could happen.

Whatever happens, there is one lesson I hope we have learned: when a new agent starts spreading in the human population, our first response has to be openness, not secrecy. The spread of SARS could have been entirely avoided if the Chinese had been open with their own population and the world when the infection first became evident. Sure, openness can lead to overreaction. I believe that the press has a responsibility in such circumstances to warn the world but also to ameliorate the inevitable fear response by putting the danger in perspective. I wrote about the responsibility of the press in the Wall Street Journal in late April and received many letters of thanks from people who thought the epidemic of fear accompanying the outbreak of SARS was an overreaction.

This is not the first and will not be the last virus to jump from an animal reservoir to humans. These natural occurrences are as likely, and maybe more likely, to face us than a man-made epidemic generated by a terrorist. We need to be vigilant, then open and effective in our response if we are to avoid replays of the SARS events. It is hard to stay vigilant when years may pass without an incident but we need long memories and the political will to stay the course. The moment will come when we will be thankful.
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