Sneezes richochet around the office like gunshots on the opening day of hunting season. Up and down the aisle on the morning bus, hacking coughs drown out the rush-hour traffic. And rows of school desks sit vacant.

This is sniffle season, the peak time for colds and flu, when those who aren't suffering coughs and nursing sore throats do their best to avoid those who are.

Colds are produced by seasonal viruses that begin their invasion in late August and continue to wreak havoc well into spring. So numerous are these resilient and persistent foes that "man can be infected with a different cold virus each year and still not experience all the known types in a lifetime," says Dr. Jack Gwaltney, a physician who specializes in cold research at the University of Virginia School of Medicine in Charlottesville.

Everyone seems to have a special cold treatment, be it applying chest unguents, forcing fluids, popping vitamin C, sucking zinc lozenges, hanging over a pot of medicinal steam or sipping Grandma's chicken soup. So varied are today's remedies -- and yet still so unsuccessful -- that one might as well try the original cold cure prescribed by Pliny the Younger in the first century: "kissing the hairy muzzle of a mouse." Presumably, if you're fast enough to catch the critter, you're on the road to recovery.

The cure for the common cold may be elusive, but the need for a cure hasn't diminished one iota since Hippocrates, the father of medicine, wrote about this malady in 400 B.C.

During the height of this season of miseries, six to eight of every 1,000 adults will have a cold at any one time. In the District alone, that translates to an estimated 4,000 to 5,000 cases every day.

Because it claims so many victims, the common cold is the leading cause of visits to a doctor's office in the United States.

The severity of the cold "is determined by how much virus you got infected with, by whether your body has ever seen that virus before, by how long ago it saw the virus, by your general age and health, and perhaps also by some seasonal factors," says Kathryn Holmes, a virologist at the Uniformed Services University of Health Sciences (USUHS) in Bethesda.

"The thing that's important in a family is that the same virus that could give me a cold could give my husband an asymptomatic infection and my 6-month-old baby croup."

Colds -- and the quest for their cure -- have perplexed scientists for thousands of years. The idea that colds are contagious first came from observing that sailors on extended voyages and people living in isolated communities were cold-free -- that is, until they came into contact again with the outside world.

By 1914, colds had been produced experimentally by infecting volunteers with nasal secretions taken from people with colds. Influenza viruses were isolated in the 1930s. But it wasn't until 1955 that researchers actually identified a virus -- in this case parainfluenza virus -- as a culprit in causing colds. In 1956, rhinovirus also was shown to cause colds, and later that year researchers isolated respiratory syncitial virus (RSV) -- an organism that can lead to viral pneumonia, croup and bronchitis in infants but produces no more than a simple cold in older children and adults.

Today, the list of cold and respiratory viruses includes coxackie viruses, adenoviruses, coronaviruses and influenza. Scientists have identified 89 subtypes of rhinovirus alone, and they believe there may be a couple hundred more.

Cold and flu viruses are found worldwide. They sweep through the population every year, thriving as the indoor humidity drops and cold temperatures force people indoors and into close contact.

Colds generally cause only upper respiratory discomfort -- sneezing, runny noses, sore throats and blocked nasal passages. These illnesses are rarely life-threatening, although in a small number of cases they can lead to more severe complications including ear infections and bronchitis.

Influenza causes many symptoms very similar to the common cold. In fact, many people who contract the flu may think they have a cold. But influenza can also be far more serious. In addition to upper respiratory symptoms, "about one third of people with the flu will have classical symptoms of fever, muscle aches, chills, malaise and prostration," says University of Virginia's Gwaltney. In very severe cases, the flu can "damage the lining of the respiratory tract," he says.

Research also shows that human influenza virus may produce new strains by reacting with animal flu viruses. There is evidence that migrating water birds -- wild ducks and geese -- spread the flu to domestic animals, including pigs, chickens and turkeys. Last year, avian flu in chickens cost U.S. breeders $62 million.

Whether wild ducks and geese have a role in "the development of new human strains of influenza is not totally worked out," says Robert Webster, a microbiologist who does influenza research for the World Health Organization at St. Jude's Children Hospital in Memphis. "Viruses in ducks rarely ever transmit directly to humans."

But sometimes, animal strains somehow become combined with human flu viruses. In 1968, when the Hong Kong influenza strain appeared, it had seven strands of nucleic acid from human influenza viruses and "one strand from a duck," Webster says. To get that kind of combination, "you have to have a double infection in a person of the human viruses and the duck virus." Whether human cold viruses can also recombine with animal strains is not known.

Despite the resilience of respiratory viruses, researchers believe that headway is being made. Part of the promise in beating colds comes from a better understanding of how they spread. Transmission may vary slightly by virus, but based on research with rhinovirus -- the organism that causes 30 percent of all colds -- scientists believe that hand-to-hand contact, sneezing and coughing are the most important transmission paths.

Cold viruses thrive in the nose, where temperatures hover at 33 degrees centigrade, just a little chillier than the rest of the body's 37 degrees. By the third day of infection, there is a viral population explosion -- one that virtually guarantees the spread of the disease and its continued survival in another unsuspecting host.

Each time a cold sufferer blows his or her nose, thousands (one study counted more than 16,000) of viral particles are shed. In studies, rhinovirus has been recovered from the hands of "40 to 90 percent of adults with colds," who managed to contaminate up to 15 percent of the room around them. The virus can survive on skin and countertops for three hours. Chances are good that the virus will be passed to the nose or the eyes: Studies show that the average adult touches both areas at least once every three hours. In some cases, even a single virus particle can produce an infection.

If there's a choice, it's probably less risky to kiss a cold sufferer than to shake hands. In one experiment, people with colds planted juicy, 90-second kisses on the lips of volunteers. Just one of 22 volunteers got colds. By comparison, 11 of 15 volunteers who touched the hands of cold sufferers became infected.

"Cells in the mouth probably don't have the right kind of receptor sites for the virus," says the University of Virginia's Gwaltney. Cell receptors work by a lock-and-key arrangement. If the virus is shaped in such a way that it fits into the receptor, which is located in the cell's outer surface, the cell's protective membrane opens like an unlocked door, allowing the virus to infect the cell. Since cells in the mouth don't seem to have the right kind of receptor to accept the virus, "you've got to either get the virus in the nose or in the eye, and it probably goes down the tear duct and gets in the nose."

Once in the nose, viruses are thought to attach to the surface of ciliated cells -- cells with microscopic hairs that move dust, mucus and other matter through the nose. Viruses are just single strands of nucleic acid -- DNA or RNA -- surrounded by a protein coat. To reproduce, they must get their nucleic acid into the cell. There it commandeers the cell's nucleus and directs the production of new virus particles by using the cell's metabolic machinery.

The body balks at this overthrow. The immune system -- the first line of defense against disease -- sends in troops, in this case white blood cells known as B cells, which produce proteins called IgA (for immunoglobulin A). The IgA -- if it recognizes the virus -- coats it and neutralizes the invaders. But if the body is run-down and can't produce enough IgA, or if the virus is new and not recognized by IgA, an infection is likely to ensue.

It used to be thought that the virus was the culprit responsible for the sneezing, drippy nose and blocked nasal passages of a cold. But now, joint research by Danish scientists and University of Virginia School of Medicine investigators suggests that "viral infection acts as a trigger" for the immune system. The body's fight against the virus -- not the virus itself -- causes symptoms such as a runny nose.

Though the drugstore shelves are crowded with cold remedies, none of these often expensive treatments offers any more than symptomatic relief.

Antibiotics are of no use at all. They "work well against bacteria . . . but viruses are completely different," says Elliott Dick, a respiratory virologist at the University of Wisconsin School of Medicine in Madison. Even if antibiotics did fight viruses, "they would also work against the cell, and might even kill the host," Dick says. "The hallmark of a good physician is that he doesn't give an antibiotic for a cold, unless you get a bacterial infection on top of it."

Chances for a cold vaccine are also dismal. Unlike influenza, which has only a few subtypes, colds can be caused by any of hundreds of varieties of viruses, complicating the drive for an inoculation. Developing a vaccine that could protect against all these viruses is not yet possible, although with new genetic engineering techniques it may be someday.

These same techniques are already producing one of the most promising treatment for colds. Interferon, a substance naturally produced by the body, can now be formed in large quantities through genetic engineering.

The good news is that numerous studies show that interferon in a nasal spray "can protect against rhinovirus when one uses it daily over a two- to four-week period," says Dr. Frederick Hayden, associate professor of internal medicine and pathology at the University of Virginia School of Medicine.

The bad news is that interferon is not very effective in battling a cold once the symptoms appear. Even worse, prolonged use of the nasal spray produces "symptoms identical to a cold."

"How far away are we from using interferon?" asks Hayden. "We need to understand the side effects," a task that he estimates will take several years. For now, the drug is being tested in families. When one member gets a cold, the others use the spray for five to seven days to see if they can protect themselves against infection. The results aren't in yet, but this brief use of interferon does not produce any side effects, Gwaltney says. One day interferon may be used to protect high-risk people -- asthmatics and those with chronic obstructive lung disease -- whose health can't afford to be compromised by a bad cold.

For the future, researchers are hoping to harness new genetic engineering techniques that may make it possible to produce a vaccine that is simultaneously effective against multiple types of cold viruses. Respiratory syncitial virus, which kills infants each year, is already a target of this effort.

Another promising avenue: All rhinoviruses attach to cells at the same location. It may therefore be possible for scientists to exploit this similarity. The result could be a drug that would block this attachment and stop the insertion of the virus into the cell. It would be like parking a car in a garage so a guest auto couldn't use the space.

"Although control of the common cold is not currently in sight, progress is being made," wrote Baylor University's Dr. Robert Couch in the Journal of Infectious Diseases. The quest "should not be considered hopeless."