Virus wars: Lessons learned from SARS

CORNELL (US)—New findings about Severe Acute Respiratory Syndrome (SARS), a virulent coronavirus that caused almost 800 deaths and infected 8,000 people in 2003, could play a role in fighting the world’s next pandemic.

Cornell University researchers have discovered key properties in coronaviruses that help explain how they invade their hosts and cross species barriers. The SARS virus, for example, originated in bats, jumped to civets (weasel-like mammals) in Chinese markets, and then to humans. Other coronaviruses cause the common cold and croup in humans.

The researchers have identified two sites—called cleavage sites—where a key structural protein on the virus gets split, activating a process that allows the virus to enter a host cell. One cleavage site was known to exist, but studies of a mutated vaccine strain of another highly virulent avian coronavirus, known as infectious bronchitis virus (IBV), revealed a second cleavage site. This discovery led Cornell researchers to search for a second cleavage site in the SARS virus, which they found in exactly the same location as in IBV.

“We can now make predictions based on cleavage sites about new viruses that might come about,” says Gary Whittaker, associate professor of virology at Cornell’s College of Veterinary Medicine and the paper’s senior author. “SARS appeared and then went away, but it is only a matter of time before similar viruses make that leap [to spread and jump species].”

Viruses often access cells by binding to receptors on the cell’s surface, but unfamiliar receptors provide barriers. However, small changes in the second cleavage site may allow coronaviruses to bypass receptors and gain entry into many cells, including those of new species. The findings provide researchers with a new context to identify virulent disease strains and could possibly lead to developing treatments.

While changes in the first cleavage site can affect a virus’s ability to infect, the study reports that changes in the second site are always necessary for increased virulence. Whittaker believes that coronaviruses may have begun with just one cleavage site but then evolved the second one.

The researchers also report that their findings have led to new insights into such animal coronaviruses as feline infectious peritonitis (FIP), the most infectious disease in cats and the feline equivalent of SARS. As expected, the FIP virus’s ability to infect cells is dictated by the same two cleavage sites, and studying FIP may contribute insights into SARS, since cats are vectors in both diseases. During the 2003 SARS outbreak, cats in a Hong Kong hotel helped transmit the disease between humans.

The study was funded by the Cornell Nanobiotechnology Center and the National Institutes of Health.

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