Scientists' cures for a cold are not all that common

  So echinacea is out. A study last month found that the popular herb didn't cure the common cold after all. Which leaves the still-sniffling masses with a burning question: Why, in this age of Wi-Fi and stem-cell magic, can't science conquer the lowly cold?

The answer: The viral culprits are much craftier than you might think.

Colds are caused by a group of bugs known as rhinoviruses. There are 101 strains, and every time one infects you, your immune system produces protective antibodies. From then on, you're immune to that strain.

The problem is that there are 100 other rhinos (as researchers call them) waiting to leap into your nasal passages. So even if you get two colds a year, it would take more than half a century to run through all the strains.

"It's hard to find something that will effectively kill the virus," says Purdue University chemist Carol Post, who studies anticold compounds. "There are so many different types."

And rhinos are only part of the story. Two other types of bug, the coxsackievirus and adenovirus, also cause coldlike symptoms. There are about 10 each of these, which adds up to a lot more sniffles before you're immune.

For decades, scientists have been seeking cold cures without much luck. One key obstacle is that any practical treatment would have to work, without side effects, against all or most of the 101 rhino strains — a tall order for any medicine.

On top of that, viruses are much sneakier than bacteria, simply because they integrate themselves so well into their targets. Unlike bacterial diseases, which invade the body, then feed off of it, viruses take over the body's cellular machinery, making them much harder to isolate and dislodge.

"They are like little body snatchers sitting inside the cell," says biochemist Tom Smith of the Donald Danforth Plant Science Center in St. Louis, an expert on cold-virus structure.

Smith, who is working on a vaccine, says cold viruses have found a nice ecological niche. They seem to infect only humans, but that leaves 6 billion possible victims. More important, cold viruses are easy to catch and easy to transmit. Unlike many bugs, which live in our intestines or blood, the germs thrive in our far-more accessible nasal passages.

"Rhinos can just go into your nose and be quite happy there," Smith says.

The viruses also excel at hiding out. Although you might stay home from work when you're really drippy and sneezy to keep from infecting your co-workers, it may not make much difference.

Even after you feel better, you're still crawling with rhinovirus and likely infecting lots of poor souls around you. Even two or three weeks later, handshakes and shared sandwiches can spread the illness.

"You're still shedding virus like crazy," Smith says.

All of these colds are costly. According to a 2003 study, the U.S. population suffers 500 million colds a year, at a cost of $40 billion. "In terms of unmet medical needs, I would put obesity first, smoking second and the common cold third," says University of Michigan internist Mark Fendrick, the study's lead author.

And as so often happens, unmet needs lead people astray. Humans don't like being told that there's no cure for their coughs and sore throats.

So they've turned to a variety of alternative treatments, such as echinacea, zinc and vitamin C. Americans bought more than $150 million worth of echinacea last year, according to the "Nutrition Business Journal."

The problem is that none of these treatments works — at least not if you believe in scientific studies.

The latest echinacea study, in the New England Journal of Medicine, examined 399 adults who had been exposed to cold viruses. The patients were broken into four groups. Three got different echinacea preparations, and one group got a placebo. About 90 percent of the subjects came down with colds, and the echinacea takers did no better than those on the placebo.

"We don't think echinacea is an effective drug," said University of Michigan epidemiologist Arnold Monto. He was not involved in this study but did one two years ago that came to a similar conclusion.

Many echinacea enthusiasts remain convinced that the herb works. Retired business executive Ron Roth, 63, of Towson, Md., said he takes it at the first signs of a cold. "I've not had a serious cold in 23 years," he said.

Brian Sanderoff, a holistic pharmacist who runs a supplement outlet in Owings Mill, Md., said echinacea is the most popular natural cold remedy at his store. He criticized the study for not using a high enough dose to be effective.

A cure for many common colds does exist. It's called pleconaril, and it works wonders against many, though not all, rhinoviruses. But three years ago, the Food and Drug Administration decided not to approve it, in large part because it seemed to reduce the effectiveness of birth-control pills.

What about those who aren't on the pill?

Tough luck, the FDA says. The cold isn't a severe enough illness to justify a drug with such side effects.

As Smith puts it: "No one will die from a cold. So any medicine has got to be safe as water."

Baltimore Sun staff writer Mariana Minaya contributed to this story.