New clues allude to origins in animals

5/2/2003

WASHINGTON - A new genetic analysis of SARS suggests the virus became a health menace by pulling the same biological trick that the AIDS virus used decades ago to trigger its global epidemic.

“These data are consistent with the hypothesis that an animal virus for which the normal host is currently unknown recently mutated and developed the ability to infect humans,” Canadian scientists said yesterday in one of two reports on the genome, or genetic blueprint, of severe acute respiratory syndrome.

The studies, which show details of SARS' genome, were rushed into print because they open doors to finding new drugs, a vaccine, and quick diagnostic tests for the deadly respiratory disease.

“We should have something to combat this epidemic in the near future,” Dr. M. Stephen Oberste, of the U. S. Centers for Disease Control and Prevention, predicted at a news briefing.

He was on the U.S. team that sequenced one of the SARS strains.

CDC got the virus from a mucus sample that Dr. Carlo Urbani took from his own body. He was the World Health Organization expert who discovered SARS, and then caught the disease and died from it in March at age 46.

A team of Canadian scientists, headed by Dr. Marco A. Marra, of the British Columbia Cancer Agency Genome Sciences Center in Vancouver, did the other study. They deciphered the genetic sequence of a SARS strain, or variety, found in a patient in Toronto.

Both profiles were published in the journal Science, after being available in a preliminary form on the Internet since mid-April.

Dr. Oberste said the data has helped in development of a new diagnostic test for SARS, now being used at research centers.

SARS is difficult to diagnose because its symptoms resemble those of influenza, ordinary pneumonia, and other respiratory ills. Individuals with symptoms, such as a high fever, who recently traveled to high-risk areas, usually are quarantined for days - sometimes unnecessarily.

Normally, the test would require Food and Drug Administration approval before going into general use in doctors' offices and hospitals around the country. But Dr. Oberste said those requirements might be waived in a public health emergency.

More than 5,600 cases of SARS have been diagnosed worldwide since March, with at least 375 deaths. At least 53 probable cases, but no confirmed deaths, have been reported in the United States.

Both gene sequencing studies confirmed that SARS is a new variety of coronavirus, a viral family whose three known branches cause mild respiratory disease in humans and more serious diseases in chickens, turkeys, pigs, and other animals.

In its genetic make-up, however, SARS differs dramatically from its cousins, and represents a fourth and previously unknown branch of the family, the Canadian group said.

Dr. Oberste said CDC's genetic profile supports the Canadian view of SARS as an animal virus that developed an ability to infect humans.

“We presume it came from an animal host, and jumped the species barrier to humans,” said Dr. Caroline Astell, of the Canadian team.

Scientists believe HIV, the cause of acquired immune deficiency syndrome, made the same leap from a monkey-only virus to humans.

Dr. Oberste said researchers now are searching for SARS's animal source by sampling viruses in pigs, ducks, chickens, turkeys, and other animals in southern China, where SARS probably originated.

The region is noted as a mixing bowl for new influenza viruses, he noted, because of close contact between farm animals and people. It allows mingling of animal and human viruses in ways that foster exchange of genetic material and the emergence of new disease-causing microbes.