Virus may have crossed species barrier
Posted: Saturday, March 29, 2003
By ANDRÉ PICARD
From Saturday's Globe and Mail
The deadly respiratory ailment SARS may have spread to humans from cattle, just like mad-cow disease.
Scientists say the infectious agent they have identified as the likely cause of severe acute respiratory syndrome is a previously unknown coronavirus, one that some researchers say looks remarkably like bovine coronavirus. In cattle, the common disease is known as "shipping fever."
Coronaviruses — which take their name from the prominent "crown" of spikes clearly visible by electron microscopy — occur in cattle, pigs, mice and humans.
The new pathogen may have crossed the species barrier and mutated.
"It's hard to be definitive at this point, but it can be hypothesized that it crossed the species barrier," Frank Plummer, scientific director at the National Microbiology Laboratory in Winnipeg, said in an interview yesterday.
He said he had examined the new coronavirus, which does not yet have a name, under an electron microscope and "it somewhat resembles several animal viruses. It's somewhere between a mouse corona, a bird corona and cow corona."
Dr. Plummer said that many new diseases have jumped from animals to humans in recent years, including HIV-AIDS, bovine spongiform encephalopathy [commonly known as mad-cow disease and in humans, Creutzfeldt-Jakob disease] and Ebola virus, often with deadly consequences. "As we change the way we interact with our environment, these things are going to occur, new diseases are going to emerge," he said.
While much of the attention of the scientific world has focused on the new coronavirus, Dr. Plummer said it is necessary to keep an open mind. In many of the samples analyzed, researchers have also found metapneumovirus, which comes from a family of viruses that usually cause respiratory ailments in children.
"At this point, we don't know if there are two separate epidemics, or if these two viruses somehow work together to cause SARS. There are still pieces of the puzzle missing."
Worldwide, there have been 1,485 SARS cases, including 54 deaths. In Canada, there have been 29 confirmed cases, including three deaths.
World Health Organization officials now say that the first known case of SARS occurred on Nov. 16, 2002, in Foshan, China. The city is located in Guangdong province, an agricultural area where there are large cattle farms. Guangdong is also a major supplier of food to Hong Kong, which has been hit hardest by SARS.
The Canadian outbreak, however, has its origins in a chance encounter in the elevator of the Metropole Hotel in Hong Kong on Feb. 21 of this year. There, a Toronto woman and a Vancouver man crossed paths with a professor from Guangdong who was infected with SARS.
Researchers now believe that professor was a "super-spreader," a modern-day Typhoid Mary who spread the disease readily to others. It is well-established that some people shed viruses much more readily than others, making them particularly infectious.
But viruses often lose their potency as they are passed on to others, and that may explain why the disease may be becoming less infectious and less deadly with each passing day.
After months of denial, China has acknowledged that the unusual pneumonia epidemic that started there last November was indeed SARS. It has just opened its doors to WHO investigators and it has agreed to start releasing daily statistics, like every other affected country.
Like a common cold, SARS is spread by droplets, and appears to be spread only by face-to-face contact. Virtually all the cases in Canada are among family members of those originally infected and health-care workers who treated them.
Containment measures, including quarantine of those affected and those who may have come in contact with SARS in Toronto, have been put into place to stop the spread of the disease.
Send page by E-Mail