Top scientist doubts link to coronavirus
Only 40% of SARS patients show signs of suspect virus
nationalpost.com
Brad Evenson
National Post
Wednesday, April 23, 2003
CREDIT: Glenn Lowson, National Post
The death toll from SARS rose again yesterday, bringing to 15 the number of people who have died from the disease in Canada. Ontario Health Minister Tony Clement, far left, said at a news conference in Toronto yesterday that up to 100 more people will be reassigned to Toronto public health units to relieve exhausted staff.
Canada's top virus hunter, Francis Plummer, a veteran scientist who has spent 20 years tracking AIDS and other deadly infections around the globe, said he is not convinced by the theory that SARS is caused by a rogue strain of coronavirus.
Dr. Plummer said tests show only 40% of Canadian SARS patients have the suspect virus in their tissue samples and even these patients have small amounts of it. Moreover, some people who test positive for coronavirus have no SARS symptoms.
"The link between SARS and the virus is quite weak," said Dr. Plummer, scientific director of the National Microbiology Laboratory in Winnipeg.
Although labs in Hong Kong and the United States have found similar results, scientists there have not been as vocally skeptical of coronavirus, identified shortly after SARS turned up in Hong Kong and Canada. But researchers agree no test can definitively rule in or exclude SARS at this time.
Dr. Julie Gerberding, head of the U.S. Centers for Disease Control and a proponent of the coronavirus theory, said there may be good reasons for the discrepancy between the number of cases and the number of patients who test positive for coronavirus.
"First and foremost is probably because [patients] don't have SARS and they don't have coronavirus infection," she told a briefing yesterday. "They have some other respiratory illness that's caused by something else. Another explanation is that although we have tests that can identify it when it's present, we don't know how sensitive they are."
Making things more difficult, said Dr. Gerberding, is that if a specimen is not taken early enough in the disease's progression, the test might not detect the presence of a virus.
"Even with influenza, which is an illness that we have very good tests for, if we don't do certain tests early in the course of influenza, the tests are negative -- they're simply done too late," said Dr. Gerberding.
Scientists now use two methods to search for a cause of SARS.
In the first, they take nasopharyngeal fluid -- nasal swabs -- within 72 hours of symptoms and test the samples directly for the presence of coronavirus using a tool called PCR. This tool is so sensitive it can detect the genetic material of a single virus and amplify it many times. So far, about 40% of Canadian SARS patients have tested positive.
In the second method, doctors take blood samples from SARS patients and test the serum for antibodies.
Ordinarily, the body produces these tiny proteins when exposed to foreign invaders, like a coronavirus. The process takes six days to three weeks. Yet only about one-third of SARS patients in Canada test positive for antibodies to coronavirus, said Dr. Plummer.
"To me, that is very, very odd."
Dr. Plummer notes all the Canadian cases of SARS have been linked by direct exposure to infected patients, so one would assume that all cases would test positive for the same virus. Yet they don't.
And while some SARS carriers seem to be extremely infectious, earning the nickname "super spreaders," others spread it less readily. For example, a single patient who travelled from Hong Kong spread the disease to dozens of others in Canada. Yet among the 39 cases of SARS in the United States, 37 were travellers who were probably infected abroad, while only two people were infected in the United States.
Although coronavirus is still a leading candidate, many scientists believe SARS may be linked to human paramyxovirus, identified by Dr. Plummer's lab several weeks ago as a potential cause. However, other researchers think the virus is simply an "innocent bystander" that just happens to be present in many people, including SARS patients.
SARS UPDATES:
Worldwide, the SARS death toll rose yesterday to 229, with 3,947 probable cases. In Canada, there are 324 probable or suspected cases of SARS and 15 deaths.
- - -
The SARS outbreak is a "national emergency" that requires the federal government to pay 90% of the costs to contain it, Liberal leadership hopeful Sheila Copps said yesterday. But Health Minister Anne McLellan said there is no national emergency and that to suggest otherwise is a "huge overreaction." The comments came as Toronto Mayor Mel Lastman and Ontario Premier Ernie Eves called for help from Ottawa.
- - -
The 450 or so people who were quarantined after attending a Montreal business seminar with a man who later became ill with SARS were released yesterday, 10 days after the scare. None came down with symptoms.
- - -
With the recognition yesterday that a businessman had been infected without leaving the country, Britain was yesterday deemed a "SARS-affected area." This "local chain of transmission" -- the man was infected during a meeting in London with a Hong Kong colleague who later became ill -- puts Britain in the company of Vietnam, Hong Kong, China, Canada, Taiwan, Singapore and the United States.
- - -
Swimming and Sumo wrestling joined rugby, soccer and polo yesterday as sports that have had major events cancelled due to SARS. The International Swimming Federation said two marathons scheduled for June in Hong Kong and China's Ginzheng City will be called off, as will the Japan Sumo Association's exhibition bouts in South Korea.
- - -
An already strained Canadian tourism industry learned yesterday Canadians are banned from the tropical, ecotourism hot spot of Belize until further notice, and Belgians have been warned not to travel to Toronto. There was also an order from Kabul that Afghanis not travel to such SARS-affected regions as Toronto.
- - -
Ontario's tour bus operators held an emergency meeting yesterday in Toronto to plan their strategy for coping with fears about SARS. Brian Crow, head of the Ontario Motor Coach Association, said many people have a perception that Toronto is unsafe and the result has been plummeting business, including one coach owner who lost $300,000 in business in just two weeks.
- - -
Health Canada has invited experts from the World Health Organization, the U.S. Centers for Disease Control, the Pan American Health Organization, and Britain to gather next week in Canada for a brainstorm session on containment measures for SARS. Dr. Paul Gully, senior director-general of the department's population and public health branch, said the meeting will be an attempt to "take stock and say ... What's the best estimate of where SARS- - - is going in this country?"
Singapore's Ministry of Education is distributing about 500,000 thermometers for its students to check themselves for fever twice a day to prevent the spread of SARS. Singapore has had 186 cases of SARS and 16 deaths.
- - -
China has developed a cheap and easy test to diagnose SARS within an hour, the country's state-run media reported yesterday. The method, lauded as an "absolutely certain indicator," uses a modified protein to detect the presence of an antibody the body produces in response to SARS infection.
Compiled by Joe Brean, National Post |
