·  SARS Breeds Threat To Taiwan Tech   ·  Sex And Cars Take On SARS   ·  Drug Does Not Work Against SARS   ·  Special Web Sites Help Scientists Fight SARS   ·  Even With SARS, Globalization Marches On   ·  Aftershock   ·  Keeping Bugs At Bay   ·  Stopping the Killer Virus

The SARS virus is most probably a coronavirus, the type of virus responsible for up to 30% of common colds. One theory has it that SARS originated in an animal and jumped to a human. The SARS coronavirus appears to be different from all other known coronaviruses, including animal ones. But it could turn out to be a mutation or cross strain of one or several coronaviruses seen in cows, birds and pigs. It could also, however, be a mutation of another human coronavirus.

Coronaviruses have apparently jumped species before: Dr. Konstantin "Gus" Kousoulas, a professor at Louisiana State University who studies coronaviruses in cattle, published a paper back in 1993 describing a bovine-like coronavirus strain in a child in Germany. Could that strain have been related to today's SARS? Dr. Kousoulas thinks it's possible. But Dr. Klaus Stohr of the World Health Organization is skeptical, and says it's too early to tell.

The German child's symptoms were diarrheal, not respiratory. But in animals, scientists have seen a coronavirus switch from being a diarrheal disease to a respiratory disease as the virus becomes lodged in a different tissue and genetically evolves. A respiratory coronavirus seen in chickens causes gasping, coughing and watery eyes, among other symptoms. Some human patients have reported diarrheal symptoms in the current SARS outbreak.

In animals, as we've seen in SARS, some coronavirus patients die while others make a full recovery. Veterinary doctors say some coronaviruses cause no symptoms at all. If SARS acts similarly, it's possible many people could have caught SARS at one time or another and not exhibited symptoms. SARS could also have been dormant: Coronaviruses in cattle can remain latent until the host suffers some stress--when being moved, for example. In that case, the virus turns into a respiratory disease known as "shipping fever." Just as animals develop immunity to coronaviruses, people could have developed immunity or partial immunity by catching a similar viral strain.

But scientists working at the World Health Organization and in its network of laboratories say it doesn't appear SARS has spent much time in the human population. "There is no evidence that SARS has appeared in the past. However, this cannot be excluded," says Dr. Hans-Dieter Klenk, a scientist at Germany's Marburg University. Dr. Stohr stresses that hundreds of people in the U.S. and Hong Kong have been tested--people who have never had SARS--and none of them appear to have developed antibodies to SARS or any close relation of it.

There are a number of vaccines on the market to combat coronaviruses in chickens and cattle, as well as pigs, cats and dogs. Publicly traded companies that have been involved with the development of these vaccines include Wyeth (nyse: WYE - news - people ), Schering-Plough (nyse: SGP - news - people ), Heska (nasdaq: HSKA - news - people ), Pfizer (nyse: PFE - news - people ), Merck (nyse: MRK - news - people ), Aventis (nyse: AVE - news - people ), Synbiotics (otc: SBIO - news - people ), ImmuCell (nasdaq: ICCC - news - people ) and Charles River (nyse: CRL - news - people ). Some of these companies have been drafted by the World Health Organization and its network in the fight against SARS. Aventis, for one, was contacted by the Center for Disease Control and Prevention on April 3, and has shipped it cell samples.

Granted, some of the animal vaccines don't work well, if at all--and the bar for human vaccines will be higher. Further complicating matters is the coronavirus' propensity to mutate. A coronavirus is a single-stranded RNA virus that can change rapidly, much like an influenza virus. Every time a new strain surfaces, a new vaccine has to be made. Dr. Carol Cardona, a veterinarian at the University of California at Davis, says that chickens are often vaccinated for coronaviruses multiple times because the virus keeps changing. Still, LSU's Kousoulas says it could take as little as six months to create a vaccine for humans, although it would need to be thoroughly tested on animals first.

Stohr says once a vaccine is made, it's possible a person could be given a SARS shot or a vaccine booster annually, as is done for the flu. "It's more important to control and influence where it's going to go," he says, "rather than speculate on where it comes from."