CBC In Depth
Amina Ali and Rachelle Younglai, CBC News Online | Updated August 14, 2003

One month after the World Health Organization declared severe acute respiratory syndrome (SARS) to be a worldwide threat, researchers confirmed the identity of the virus that causes the disease.

Identifying the SARS coronovirus could lead to faster and better diagnosis and treatment but a vaccine to prevent it is likely still years away. Hundreds of scientists in 11 disease control centres in nine countries are working around the clock, pooling their resources and findings via a secure Web site and daily teleconferences. Because so little is known about the transmission of the disease, WHO has limited the research to labs that are equipped to handle deadly pathogens.

On April 16, the World Health Organization officially confirmed a member of the coronavirus family never before seen in humans causes SARS. The process of identifying a new pathogen is rigorous. It is not enough to simply identify the microbe by how it looks. It must be isolated, grown in isolation and then the cultured germs must be able to recreate the disease in a test animal.

Dutch scientists fulfilled the final condition by infecting monkeys with the SARS coronavirus. The animals developed the same symptoms as humans with SARS.

Here's where scientists are as of mid-August.

Scientists have taken tissue and blood samples from patients and compared the infected samples to samples from healthy individuals. Once the aberration was detected they started the process of trying to identify its shape and structure and determine what category and family its source belongs to.

Isolating the virus

Hong Kong scientists were able to isolate the virus. Isolating the virus allowed scientists to start characterizing the agent, to determine its relationship with known viruses and subsequently define it.

Culturing the virus

Although culturing viruses is difficult because they only replicate within a living cell, there have been reports that researchers at labs across the world, including Canada's microbiology lab in Winnipeg, have been able to grow the virus.

Antibody and genetic tests

CDC researchers developed antibody and genetic tests to help confirm SARS cases. If a patient has a positive antibody response to the new coronavirus, scientists say it may be evidence there is a link with SARS.

"When we see a positive test at the end of illness and a negative test at the beginning of the illness, that's really strong evidence of coronavirus infection. It still doesn't mean it's the cause of SARS, but it's pretty strong evidence that that's what we have," said Dr. Julie Gerberding of CDC. "It's a good clue, but again, it's just not proof."

The antibody test is in its infancy and the accuracy and reliability of the test still need to be verified. To draw any conclusions scientists must have thousands of samples from those who are infected as well as from those who are not.

WHO scientists plan to discuss a strategy for developing a "reliable and dependable" diagnostic test for use in both developed and developing countries. Current tests can identify the virus's genetic material even in people who aren't showing symptoms of SARS, but the genetic tests do not distinguish between live viruses and those that do not cause disease.

Sequencing the virus

On April 12, scientists at the Michael Smith Genome Sciences Centre in British Columbia mapped the genome of SARS-associated coronavirus. The purified sample came from a SARS patient in Toronto.

The B.C. scientists saw similarities to bird, cow and mouse coronaviruses but also some differences. By comparing the Canadian sequence to those from other labs around the world, researchers hope to track possible mutations in the virus. Knowing the sequence will allow researchers to make viral proteins that may help treat SARS, and may provide the basis for a eventual vaccine.

On May 1, scientists authenticated the genomic maps of the Canadian sequence and a nearly identical one from a U.S.-led team. Publishing the sequences in a peer-reviewed journal lends credibility to the research.


What the public seems to find so difficult is not so much the ferocity of the outbreak but the ambiguity surrounding the transmission of the disease.

At first WHO said the virus was transmitted by face-to-face exposure to droplets released when an infected person coughs or sneezes. This continues to be the leading mode of transmission for SARS. Dozens of people who live in the same Hong Kong residence became infected raising concerns that the virus may be carried by water or by vaporized droplets that remain in the air and are then inhaled. Another theory is that the virus may live outside of the body for two to three hours thus contaminating surface areas.

WHO posted the first data on the resilience of the SARS coronavirus online on May 4. Test results suggest the virus is stable in feces and urine at room temperature for at least one or two days. It can survive up to four days in the higher pH of stool from diarrhea patients. The finding supports the sewage theory of spread in the Hong Kong apartment building, but scientists don't know if the amount of virus on surfaces is enough to infect people.

Like many other viruses, the SARS coronavirus can survive freezing temperatures. Hong Kong scientists found common disinfectants can kill the virus. Coughing and sneezing continue to be the main way the virus spreads, according to public health officials in Toronto.

Doctors are using anti-viral therapy to try to prevent the virus from replicating but so far this has not been successful.


Despite the progress, there are many other questions that need answering in order to draw any conclusions: how are the outbreaks linked to other countries? How does the disease spread? At what stage is the virus the most active? How much of the virus is needed to infect people? How long are people infectious? What is the incubation period? How can SARS be diagnosed?

One leading theory suggests that the SARS virus jumped to humans from an animal species. Another suggests a microbe mutated into the more virulent form in humans? There has also been some speculation that it could be a manmade virus but CDC dismisses this theory.

After weeks of delay, China permitted a team of WHO experts to enter the country in early April to observe SARS treatment and infection control measures at hospitals.

WHO experts tried to track the source of SARS in Foshan city, where the first case was reported in November 2002, and Guangzhou city. Viruses can more easily jump species in areas where people and animals are found in close quarters.



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The SARS (Campbell) Commission

New England Journal of Medicine

Canadian Medical Association

Ontario Ministry of Health Update on SARS

Vancouver SARS page

Hong Kong SARS page

WHO: SARS Outbreak News

World Health Organization travel advisory

Health Canada SARS site

Toronto Public Health's SARS site

Health Canada travel advisory

Severe Acute Respiratory Syndrome (SARS), Centers for Disease Control and Prevention

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