By Margarita Nahapetyan
Researchers at the University of Wisconsin, the University of Maryland and the J. Craig Venter Institute say that they got closer to one of medicine's elusive goals - finding a cure for the common cold, known as rhinovirus.
Rhinoviruses cause about half of all colds. Viruses survive by hijacking other cells to serve as hosts, and when rhinoviruses occur, the cells they invade settle themselves in the nose. There are more than one hundred known versions of the rhinovirus. These versions are constantly mutating and have very little in common other than causing similar symptoms of fever, runny nose, headaches and pains.
For their new study, the scientists analyzed about 99 known strains that had been collected from human noses and stored, frozen, in a virus lab. The rhinovirus has a genome of nearly 7,000 chemical units, which encode the information to make the ten proteins that do everything the virus needs in order to infect cells and make and spread more viruses. The scientists also examined fresh samples collected from the field.
By comparing these ninety nine genomes with one another, the researchers were able to arrange them in a family tree based on similarities in their genomes. The result of their work is a family tree of sorts of the different viruses. The viruses fit into about 15 different families. Members of each family have much in common and may respond the same way to future medicines. Doctors have been frustrated because today's medications only cure the symptoms of a cold. For example, a decongestant will dry one's sinuses, and pain remedies will ease the body aches a person gets. But for now, people do not have a choice other than to let the virus itself run its course.
"We have had bits and pieces of these things for a long time," said Ann Palmenberg, chairwoman of the Institute for Molecular Virology at the University of Wisconsin in Madison and the study's lead author. "Now, we have the full genome sequences and we can put them into evolutionary perspective."
The researchers also believe that they may find possibilities to design drugs to fight the rhinoviruses, which use their single gene to move rapidly from person to person, causing symptoms that range from irritating sniffles to pneumonia. Instead of designing one drug to cure the common cold, several may be needed because the virus mutates so efficiently," said the senior author of the study, Dr. Stephen B. Liggett, director of cardiopulmonary genomics at the University of Maryland School of Medicine. "We may end up having four or five drugs, and you would need a test at your doctor's office to know which drug will work," Liggett said in a telephone interview on Thursday.
This is because any rhinovirus has just one gene, which in its turn makes a giant protein that turns out to do very little or nothing before it gets divided into 11 smaller pieces by an enzyme called a protease. Researchers tried to attack this big, clumsy protein before. "The first drug, the virus mutated around it," Liggett said. "But now that we have all the pieces we can begin to understand what areas are not so flexible. We can begin to do some more rational drug design."
"This is a new insight," says co-investigator Claire M. Fraser-Liggett, Ph.D., director of the Institute for Genome Sciences and professor of medicine and microbiology at the University of Maryland School of Medicine. "We would not have had any sort of intuition about this had it not been revealed through genome analysis. Information that comes from this discovery might present a completely different approach in terms of therapy."
Besides alleviating the common cold torture familiar to everyone, a true cold-fighting drug could also help the twenty million people who suffer from asthma and the millions of others with chronic obstructive pulmonary disease. The common cold virus is believed to trigger half of all asthma attacks.
Over the next three years, the researchers plan to look at one thousand additional rhinovirus genomes collected from noses all over the country in order to find out which strains are dangerous for asthma and cause other serious infections. Those, and not the strains that cause mere head colds, are likely to be candidates for treatment, said Ann C. Palmenberg.
Although not linked with anything dangerous, human rhinoviruses are associated with significant sickness. Besides being responsible for half of all asthma attacks they are also a factor in bronchitis, sinusitis, middle ear infections and pneumonia. In elderly patients, infants, and those with asthma or lowered immune systems, complications from a cold can be dangerous enough. It is estimated that in the United States the common cold contributes to 30 to 50 per cent of time lost from work for adults and 60 to 80 per cent of time lost from school for children- with direct and indirect costs of about $60 billion every year.