Stamping out SARS: scientists race to stop the spread of a mysterious disease.

The hottest accessory to hit Asia last spring was the surgical facemask. But this was no fashion statement Chinese citizens sported masks to shield their lungs from a new and fast-spreading disease called SARS severe acute respiratory syndrome).

When SARS first appeared in southern China last November, doctors thought the illness--which spreads through the air and causes flulike symptoms--was a new form of pneumonia (see diagram, page 9). It turned out to be far more lethal. At press time, SANS had infected over 8,000 people in 30 countries and killed 792. But a fast response by health care workers worldwide has largely controlled the spread of the disease. Can science stamp out SARS for good?

Unsolved Mystery

"It's too early to tell how long SARS will be around," says Paul Rota, a virologist (virus scientist) at the U.S. Center for Disease Control (CDC). So far, scientists know the disease causing microbe is a type of coronavirus--a family of viruses known to infect the respiratory tract (lungs and airways) of humans, pigs, cats, and chickens. All coronaviruses share the same basic structure: genetic material surrounded by a spiky protein crown. But while most cause mild illnesses like the common cold, the SARS virus kills 8 percent of those it infects. Victims die of respiratory failure.

Like all viruses, the SARS virus is a parasite: it can only survive in a host (animal or plant in which another organism lives). Viruses hijack a host cell's machinery in order to replicate (reproduce)--harming the host in the process. For example, it's hard to smell when you have a cold because the cold virus uses your nasal cells to replicate. But a cold won't kill you. A few viruses like SARS, however; can cause so much damage they kill the person. "The question is, why does the SARS virus cause such severe disease?" asks Rota.

Clues to this mystery lie in the virus's genome (an organism's genetic material). Rota and his co-workers sequenced the SARS virus's RNA. Like the DNA of plants and animals, RNA is a string of chemicals arranged in a specific order. Rota's team compared the sequence with that of other coronaviruses. Only a few genetic changes, or mutations, in the sequence make SARS vastly different from other coronaviruses. Rota hopes to uncover how and why such changes can prove so deadly.

Under Control?

While there's no cure for SARS, doctors now know how to curb the disease. Patients are kept under quarantine (isolation) until they're no longer contagious. And about 95 percent of all SARS patients fully recover. Why? Most likely, they have a healthy immune system (organs, tissues, and white blood cells that help fight invading organisms), explains microbiologist Amy Cheng Vollmer of Swarthmore College.

Harmful microbes constantly enter the body through the skin, eyes, mouth, and nose. But a well-balanced diet, plenty of sleep, and good hygiene keep the immune system on alert.

Last May, scientists tracked the origin of the SARS virus to civet cats, weasel-Mike wildcats whose meat is a Chinese delicacy. But it's still unclear whether humans contracted the virus while handling the animals at food markets in southern China, or if they got it from a still unknown source.

That's why the best bet for squashing future outbreaks will be a new vaccine (injection of killed or weakened virus). A vaccine preps the immune system to combat a virus by pumping up the number of specialized white blood cells on patrol. Scientists will eventually develop a vaccine for humans, says Michael Buchmeier, a coronavirus expert at the Scripps Research Institute in La Jolla, California: It's just a matter of time. SARS is not going to destroy the world."

ANATOMY OF THE SARS VIRUS

The SARS virus uses an infected human host to crank out thousands of SARS viral particles every hour.

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MASKING THE FEAR

"Designer" masks may be creative, but the best ones need a respirator that fitters out particles below 0.3 microns in diameter (a human hair is roughly 100 microns).

NEW DISEASES ON THE RISE

Over 35 new diseases have been discovered in the past 30 years, including HIV/AIDS, West Nile Virus, and now SARS.

But where do they all come from? Old, harmless human viruses can mutate into new killers. They can also lurk in unknown animal hosts--like monkeys (the origin of HIV, the virus that causes AIDS) and civet cats (SARS)--waiting to infect humans.

The human immune system has adapted over thousands of years to protect against viruses found in pets and livestock. But our immune systems haven't learned to recognize the microbes found in exotic animals.

"New diseases spring up when people come in close contact with species they don't normally interact with," says microbiologist Amy Cheng Vollmer. As the global population booms and human developments creep into nature, people encounter exotic species much more often--creating the perfect opportunity for a virus to jump into new host species.

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Did You Know?

* The concept of using quarantine to stem the spread of disease began in Venice, Italy, in the 14th century as a result of the Black Plague. Officials required that ships anchor out of port for 40 days before sailors could dock.

* The spiky proteins on the surface of the SARS virus bind to the host cell to help the virus enter.

* SARS is a mild disease compared with Ebola, which kills over 90 percent of those it infects. But SARS poses a bigger public health risk because it can spread much more quickly before it's detected.

Cross-Curricular Connection

History/Social Studies: Many diseases that were virtually eradicated in the U.S. by vaccination still linger in underdeveloped countries. Research one such disease and write a brief report describing the disease, its cause and symptoms, where it's prevalent, and possible solutions.

Critical Thinking: Antiviral drugs work by blocking a virus at different stages after infection. Review the viral replication cycle from beginning to end (p. 9). What might be the best stage for medication to target the SARS virus? Why?

Resources

For updated infection rates and a wealth of information on SARS, visit the CDC at www.cdc.gov/ncidod/sars/ or the World Health Organization at www.who.int/en

These two articles describe scientists' response to the outbreak: "Tracking SARS," Newsweek, April 28, 2003; "The Search for SARS Past May Help Predict Its Future," The New York Times, May 20, 2003

This site has an illustrated step-by-step explanation of how the immune system destroys viruses: www.cancerresearch.org/immresp.html

Name: --

Stamping Out SARS

Directions: Fill in the blanks to complete the sentences.

1. A -- is a scientist who studies viruses.

2. SARS first appeared in -- last November. At first, scientists
thought it was a new form of --.

3. Scientists discovered the SARS virus is a type of --, a family of
viruses known to infect the -- of humans, pigs, and cats.

4. Like all viruses, the SARS virus is a --. It can only survive in a
--. It aims to hijack a cell's machinery in order to --.

5. As of now, the most effective way to curb the disease is
to -- infected people. About 95 percent of SARS patients recover.
Most likely, it's because they have a healthy --.

ANSWERS

1. virologist 2. Southern China, pneumonia 3. coronavirus, respiratory tract 4. parasite, host organism, replicate 5. quarantine, immune system