SARS Still Has the Experts Guessing
In New Zealand, Maori tribesmen have been warned against performing their customary nose-rubbing greeting on tourists. In Thailand, visitors from affected countries are given mandatory medical checkups at airports and seaports and are required to wear facemasks throughout their stay.
Such masks -- many of them boldly and stylishly decorated-- are now sported everywhere on the streets of Hong Kong.
Worldwide, severe acute respiratory syndrome, known as SARS, has infected more than 2,400 people and killed at least 89, with five new deaths added Saturday. It has caused school closures, travel restrictions, the withdrawal of diplomats, the quarantine of thousands and the abrupt cancellation of sports contests, scientific meetings and rock concerts.
The outbreak has sent out ominous tendrils from the Guangdong region of southern China, where it is believed to have originated, to other parts of the world including Canada and the United States. In the U.S., 115 cases have been tallied in 29 states.
Experts say the eventual ranking of SARS in the laundry list of plagues and scourges that pick off countless human beings every year depends on many unknowns. A poorly understood confluence of biology, ecology and human activity dictates whether a tiny, invisible microbe spreads through the world wreaking havoc or shows some muscle and then falters, fades, or ends up marginalized in slim pockets of the world.
“I don’t think we really know where we’re going yet on this one; we’re in the third or fourth line of a three-act play,” said Dr. Michael Osterholm, director of the Center for Infectious Disease Research and Policy at the University of Minnesota’s School of Public Health. “It really is a function, now, of letting the virus show its hand.”
Osterholm and others praised the efforts of the World Health Organization, the federal Centers for Disease Control and Prevention and other public health bodies as efficient and appropriate. Cases have been quickly tracked and exposed individuals quarantined. Health-care workers wear high-filtration masks when caring for patients, who are treated in reverse- pressure hospital rooms that allow air to flow in but not out.
The likely viral culprit has already been isolated and is under analysis. A definitive, diagnostic test for that virus should be available within weeks, and the quest for a vaccine is underway.
Experts also point out by way of context that an illness we take for granted is far more lethal than SARS has been. Each year, the influenza virus infects 10% to 20% of Americans, hospitalizing 114,000 and killing 36,000. Worldwide, influenza kills 250,000 to 500,000 people annually.
“Obviously, SARS is of concern, but the number of deaths so far is still dwarfed by the number of people who die each week from influenza-related complications,” said Dr. David Pegues, director of infectious diseases control at UCLA Medical Center.
By far the top candidate for the cause of SARS is a previously unknown virus that belongs to the coronavirus family. Coronaviruses have never been shown to cause dangerous disease in humans. Discovered in the 1960s, they were named for the spike-like structures on their surfaces, which give the appearance of a crown, or corona. They cause about 20% to 30% of the cases of the common cold.
Because the viruses have not been considered dangerous, they haven’t attracted much research or medical concern, said coronavirus expert Dr. Michael Lai, professor of molecular microbiology and immunology at USC’s Keck School of Medicine.
In contrast, specialists have been hugely worried about the emergence of a deadly, new strain of influenza, like the one that killed 20 million to 50 million people worldwide in 1918.
The flu virus is such a threat because it is very prone to accumulating genetic changes. It readily treats chunks of its genome like noxious trading cards, swapping them with chunks from related viruses in pigs and birds -- sometimes coming up with lethal new variants.
The prospect of a deadly new flu still looms large. However, the emergence of a virulent new coronavirus shouldn’t be a big surprise, said Dr. Donald Burke, professor of international health and epidemiology at Johns Hopkins University Bloomberg School of Public Health.
There are many coronaviruses that cause lethal respiratory sicknesses and diarrhea in pigs, birds, cats and cows. Coronaviruses are also adept at trading genetic material should they come into contact with these related viruses.
Determining a genetic sequence of the SARS virus will provide valuable clues as to its origins and how to fight it.
But it will not predict how the virus will act. For all of today’s molecular knowledge, there remain a host of unsolved mysteries about viruses -- such as what causes a strain to invade one creature and not another, why some viruses cause infections seasonally and others year-round, and why some can survive in the air for long periods while others wimp out quickly when deprived of bodily fluids.
The ability of a virus to get from victim to victim is key to the impact it makes.
The Ebola virus, fodder for terrifying tales in books and feature films, kills at least half of the people it infects -- more than 80%, in some recorded outbreaks. But it remains marginalized in parts of Africa because it acts swiftly and infection requires direct exposure to contaminated blood or other secretions.
The flu virus, in contrast, causes far more deaths because it can survive when buoyed into the air and thus spreads like wildfire -- even though, in a typical year, fewer than one-tenth of a percent of those who get it die. Even the 1918 flu killed just an estimated 3% of its victims, said Alison Galvani, a UC Berkeley flu researcher.
That is a lower percentage than the number so far for SARS, which is hovering at around 3.5%.
So it is considered fortunate that SARS is far less contagious. Evidence suggests it is mostly spread by droplets and requires close contact, although concerns about some airborne and waterborne transmission still remain.
Dr. Arnold Monto, professor of epidemiology at the University of Michigan’s School of Public Health, said this offers hope the outbreak can be contained by such measures as facemasks, quarantining and reverse pressure rooms.
“Flu could not be stopped this way,” Monto said.
Key to halting the disease and determining its impact will be the definitive, diagnostic test for the virus. Only this can reveal with certainty who is infected with SARS -- and whether there are many more cases than are known. It is common, experts say, for death rate percentages to be overestimated at the start of an outbreak of a disease, because, at first, only the sickest are identified.
While everyone welcomes a lower mortality rate, the more infected people walking around with mild or no symptoms, the harder it is to wipe out a disease. Asymptomatic carriers have made the effort to eradicate polio worldwide far more daunting than was the elimination of the smallpox virus.
Other factors will determine how the virus spreads and whether efforts to curtail it will bear fruit.
Are some people “super-shedders” of the virus? Super-shedders are people who, for unknown reasons, slough off high quantities of a virus or bacterium, and are extra-infectious. Has the human species been exposed to a virus closely related enough to SARS to possess some degree of immunity toward it? And how soon will a good vaccine be found?
To scientists who monitor infectious diseases, the emergence of SARS serves as a reminder that viruses remain mysterious and unpredictable foes. Today, as people fly across the globe dragging all manner of exotic, invisible germs in their wake, these creatures are showing their cards as never before.
“Am I surprised by this event? No. Would I have told you it was going to be a coronavirus? No,” said Osterholm. “I think, today, we shouldn’t be surprised by anything that Mother Nature throws at us.”
