Medical Examiner

The Last Big Virus

SARS—a fire drill for the avian flu?

Shopping for a response to avian flu? Look to SARS.

The recent death of a girl from avian flu in a Chinese village, along with this week’s report of the eighth confirmed human death from the virus in Indonesia, underscore the reasons to fear a human avian-flu pandemic. But it isn’t all bad news on the scary virus front. Remember SARS? Chances are it is gone forever.

Exactly three years ago, a village Communist Party chief in Guangdong province went to bed with a bad cough after chowing down on delicacies such as civet cat and snake. A few days later he was admitted to a hospital, where he spread the disease to his nurses. Within weeks, many cities in Guangdong were full of people gasping and dying of mystery pneumonia. The Chinese government didn’t inform the world about the outbreak until March 2003, around the time that a sick businessman at a Hong Kong hotel coughed on fellow travelers from Singapore, Vietnam, Germany, and Canada. SARS (“severe acute respiratory syndrome”) swept through parts of Hong Kong, Taipei, Toronto, and other cities, killing 10 percent of the 8,000 people it sickened and setting off a panic that cost the Asian and Canadian economies $40 billion. No one seemed to have a clue about how to stop this crazy killer cough, though public health officials did their best to isolate patients while doctors treated symptoms of infection and toxic shock. And then in July 2003, after a few months in the headlines, SARS disappeared.

A tidal wave of medical literature—3,000 journal articles—has been published on SARS. All this study allows scientists to make a good case that, barring lab error or bioterrorism, SARS is unlikely to return. And if the disease does reappear, the world will be well-prepared. We’ll know what to expect and how to react.

SARS seems a feeble monster indeed compared to H5N1, the avian flu virus, which when it crosses to humans seems to kill as many as half of them. Still, the SARS fight was a wake-up call, an alarm drill, whatever you want to call it—a case study for thinking about pandemic flu.

The good news about SARS, if one can call it that, started coming in late 2003, when a recurrence of the disease infected four Guangdoners who had frequented “wet markets” where live game animals were sold. By this time, Chinese scientists had discovered that some of the Himalayan palm civet cats sold as food items in these markets carried a coronavirus that is 99.8 percent identical to the causative agent of SARS. It seemed likely that both waves of SARS patients had contracted the virus from the civet or other market animals. But unlike the first group of SARS victims, the four new patients had a different strain that produced mild cases and didn’t spread the virus further. Studies of antibodies in the population of Guangdong confirmed this finding. The evidence suggested that strains of a SARS-like virus had probably jumped from animals to humans at least a dozen times. But in only one of these transfers—the cause of the world epidemic—had the virus adapted well enough to kill and spread. That strain died out after the first four-month epidemic.

A second piece of good news came last September, when two groups of scientists reported that they had discovered the reservoir for the SARS-like virus. Horseshoe bats, another animal sold in wet markets, carried the virus in the wild but did not appear to be sickened by it. And it turned out that though the palm civet could be infected with SARS in wet markets, their wild civet cousins did not carry the disease. From these two pieces of evidence scientists were able to reconstruct the beginnings of the SARS epidemic, which likely began when droppings from a caged bat fell into a civet’s cage. As the virus mutated successfully to accommodate itself to the civet, it also acquired the capacity to infect people. But not very well. Although civets or other animals could infect people with a SARS-like virus again, a virulent, deadly attack was probably a chance, one-off event—especially since China has since banned wet markets.

Canada, which had sunk $1.2 million into developing a SARS vaccine, has apparently ditched its efforts, convinced the disease is no longer a threat. The NIH still has a portfolio of about $98 million in contracts, grants, and internal research aimed at developing therapies and a vaccine that would at least be ready for experimental use if SARS returned. But officials at the National Institute for Allergy and Infectious Disease think things are pretty well under control. “It’s not as unlikely as lightning striking twice, but there’s a good chance that SARS as we knew it—a deadly contagious virus—will not appear again,” says Stan Perlman, a virologist at the University of Iowa.

So, how much good does the apparent demise of SARS augur for the fight against flu? Some, though not much, unfortunately. In scientific terms, SARS was easier to stop and thus required less global communication and coordination than will be necessary to control a pandemic of H5N1. If the initial host country for the pandemic flu waits as long as China did to report SARS, we’re probably done for. Flu, once it gets going, is a fast-traveling bug.

While only a few of the SARS patients seem to have been so-called “super-spreaders”—capable of coughing up bubbles of virus that remained floating in the air for a couple hours—the influenza virus often floats. And it infects cells better than SARS did. (Click here for more about how the viruses spread.) In addition, SARS patients were only contagious after they got quite sick, while flu patients can be contagious for a few days before symptoms start. Eventually, isolation and tight quarantine kept SARS from spreading. Flu would be harder to quarantine, and in any case enforced quarantine is an alien concept in the United States. Rather than tossing around the idea of a military occupation here in the case of a pandemic, as President Bush has done, it would make sense for the United States to invest more scientific time and money in hospital labs and surveillance teams in Asia. In the event of a definitive human-to-human crossover, tight control efforts would then have a better shot at preventing H5N1 from breaking out around the globe. SARS showed the continued importance of the World Health Organization, a relatively small agency that opened avenues of communication and data-sharing among the world’s virus hunters and public health officials. If pandemic flu breaks out, there probably won’t be enough effective vaccines or drugs to fight the disease on a global scale, if at all. The key prescription for fighting emerging diseases, SARS has shown, is detection, communication, and good science.