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CDC Hails SARS Virus Sequencing, Discusses PCR Diagnostic Development

NEW YORK, April 14 - Officials at the US Centers for Disease Control today hailed the rapid sequencing of the coronavirus believed to cause Severe Acute Respiratory Syndrome (SARS), and discussed the PCR -based diagnostic tests they are developing.


The sequencing of the virus, which the CDC completed today, two days after a team from the University of British Columbia finished its draft, "is a scientific achievement that I don't think has ever been paralleled in our history," said Julie Gerberding, CDC director, at a press briefing this afternoon.


The speed of these sequencing efforts - which were completed just 31 days into the epidemic, is something that will enable the researchers to more rapidly develop diagnostic tests, Gerberding said.  Both the CDC group and the UBC group have published their sequences, which differ by about 10 bases, on their websites (Click here for: CDC site, UBC site.)


The CDC has also published a phylogenetic tree of the coronavirus' known proteins, and has said that analysis of the viral genome has led to the identification of open reading frames for the predicted polymerase protein, spike protein, small membrane protein, membrane protein, and nucleocapsid.


Genome analysis by CDC researchers has, however, failed to reveal an animal host from which this virus may have jumped. "We can't say it's a mouse virus or a pig virus, or any other animal virus, necessarily, because it just isn't similar enough to the known species to be able to draw those conclusions," said Gerberding.


Larry Anderson, who led the sequencing effort at the CDC, specified that the virus is distinct from the animal strains and the known human strains, occupying a distinct antigenic group.


So far, attempts to demonstrate that the virus is the cause of SARS by inserting it in animal tissues have yet to produce conclusive results, the CDC said.


But the CDC is meanwhile planning to use the completed genome draft to develop a diagnostic test. Agency researchers are already using one PCR-based test that is based on part of the viral sequence. "But if we know the whole sequence, we can create combinations of tests or more elaborate tests that are built on the same principle," said Gerberding.


Even the current version of the test "can be extremely sensitive," she added, but the agency is still more than a week away from a licensed diagnostic.


"The process of getting a test licensed is a step-wise process, just like getting a drug licensed is a step-wise process," Gerberding said. "What we're doing now is preparing the reagents and optimizing the method, so that we can get these tests out to the state laboratories are epidemiologic tools. In addition the FDA is working side by side with us to get the tests into an investigational protocol, so that we can use it for making patient care decisions."


Meanwhile, a group of researchers at the Bernhard-Nocht Institute of Tropical Medicine in Hamburg, Germany, has developed its own home-brew RT-PCR-based test, and has published the test protocol on its website. Gerberding indicated that she did not know much about this test, but was "delighted" to hear about it.

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