SARS Update

[Guest CabinDweller]

Here is a complete but succinct article demonstrating where we are and where we need to go. Also highlights the conflicting information (with the reasons behind it) presented to researchers and through them the media and through them the public.

SARS: Identifying the cause

Amina Ali and Rachelle Younglai, CBC News Online | Updated April 11, 2003

Three weeks after the World Health Organization declared severe acute respiratory syndrome (SARS) to be a worldwide threat, researchers are coming a little closer to identifying the cause. 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.

Identifying the cause of the disease has been difficult. There is much debate surrounding the type of virus involved and many questions need to be answered before any type of conclusion can be drawn and any type of treatment developed.

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. If scientists can meet these three conditions, it is the ultimate proof that the microbe is the cause of the illness. This course of proof is known as Koch's postulates, initially designed for anthrax in the late 19th century by German scientist Robert Koch.

Here's where scientists are as of early April.

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.

Scientists found two types of viruses in SARS patients - paramyxovirus, the family of viruses that includes the one causing measles, and coronavirus, a family of viruses that includes the second most common cause of colds.

On March 18, doctors in Germany and Hong Kong said they had found signs of a paramyxovirus in blood samples from SARS patients. Canadian researchers identified genetic signs of human metapneumovirus, a family of microbes that can cause measles, mumps and canine distemper, but this turned out to be a dead end.

However, a week later, scientists in Geneva and the U.S. said they found a coronavirus new to humans in the lungs and other tissue of some victims. Canadian scientists have found the coronavirus in about half of their samples.

In early April, researchers with the U.S. Centers for Disease Control and Prevention (CDC) said they were 90 per cent positive that the virus is a coronavirus, identified by its crown-like appearance.

The debate has been raging as to which virus is the cause: is paramyxovirus a byproduct of coronavirus or vice versa? Does one or both cause the microbe to mutate and become more infectious or easier to spread? Is it a new agent? And the questions go on.

"When you see both you don't know what you're dealing with," said Dr. Bhagirath Singh, director of the Institute of Infection and Immunity at the University of Western Ontario. "Labs have been running tests to learn what causes the disease, and have been unable to find anything conclusive."

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 of the test still needs to be verified. To draw any conclusions CDC must have thousands of samples from those who are infected as well as from those who are not.

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 the identity.

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 culture the virus.

According to the CDC, scientists in the Netherlands have successfully infected an animal, however results are not yet available.

Sequencing Virus

Scientists are also working on identifying the genetic makeup of the virus and are expecting results in the next week or so. If they are successful, this could aid in the creation of a rapid diagnostic test and reduce death rates by allowing doctors to identify affected patients sooner.

Dean here, let me interject for a minute.

Within weeks of the first deaths the virus was isolated under microscopes. Although actual sequencing wasn’t possible until now [ B.C. lab cracks suspected SARS code http://www.cbc.ca/stories/2003/04/12/sars_code030412 ], a DNA analysis is the primary factor that led authorities to declare this was not an act of bio-terrorism. It’s the randomness of the “base pair” that confirms this is a naturally occurring organism. [DNA is made up of repeated units called nucleotides, primarily comprising one of four bases. Two of these form together to make the rungs of the ladder in the familiar “Double Helix.” Every organic thing in the universe (well…let’s just stick with earth) is made up of these same four bases, it’s the order of them within the chromosome strand that determines on organisms characteristics. Human…amoeba…grain of rice…you get the idea. END LESSON] I mentioned last week there was a terrorism angle I wanted to discuss related to this but will start a new thread as probably only two of you have gone this far (to music… is anybody out there?).

Transmission

What the public finds 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. But then 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.

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

Theories

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? Is the cause a single or multiple agent?

One 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.

Now that China has permitted a team of WHO experts to enter the country, much more remains to be discovered.

WHO experts will start tracking the source of SARS in Foshan city, where the first case was reported in November 2002, and Guangzhou city.

http://www.cbc.ca/news/sars/