The Common Cold

The Common Cold is caused by a virus. There are over 200 known cold causing viruses the most common being the human rhinovirus of which there are over 100 different strains or serotypes causing about 50% of all colds ± 20%. The remaining 30% to 70% of colds are caused by other viruses. What matters here is that

The rhinovirus is known as an RNA virus and, because it replicates at such a rapid rate, it is possible for it to mutate into over 800 different forms once it infects a person. These mutated versions can then be passed onto other people. This makes it virtualy impossible to create a vaccine that would prevent the virus from taking hold, creating that sought after magic bullet, "The Cure for the Common Cold".

The origins of the word, "Cold", comes from the belief that being exposed to cold weather is what causes someone to, "catch", a cold. This, in fact, is not the case. It is not the weather causing a cold it, instead, is beleived to be a change in behavior during the winter months that causes us to catch colds. During the winter rather than being, "out and about", we stay in resulting in closer contact making it easier for the cold virus to make human contact leading to infection. In other words, the viruses causing colds are always present but aren't as easily spread during the warmer months of the year.

We all know what a cold is when it comes to symptoms. Stuffy runny nose, sneezing, coughing, and possibly a sore throat. Generally, one does not get a fever with a cold. If these symptoms exist along with a fever, chances are, it is not a cold but the flu. This is not to say that someone with a cold will not run a mild fever it is just not as common to have one as it is when someone has the flu.

Determining whether someone has a cold or the flu is not a straightforward diagnosis. Healthcare professionals do not always make a proper diagnosis. A good indication that someone has the flu, and not a common cold, is if the symptoms come on rapidly, ("it hit like a brick"), and if fever and a cough develop.

CATCHING A COLD

The cold virus is passed from human-to-human in the air. It can also be picked up from surfaces. Counter tops, door handles, a handshake, anything that humans come into contact with can be a source for passing the virus. A cold causing virus can be viable for several hours outside of a host. Someone with a cold sneezes in the proximity of others, they in turn breathe in the air carrying the virus. Someone sneezes into their hand and then touches a surface that is then touched by others, passing the virus.

Cold viruses thrive in the noses of humans, (animals cannot catch a cold), when someone breathes in the virus or touches their face, especially their nose, the virus travels into the nasal passage.

According to U.S. health statistics approximately 62 million people are infected every year and 50 million of these people are under age 17. It is believed that as we grow older the antibodies our bodies produce to fight cold viruses build up in our immune system.

BECOMING INFECTED

Infection begins when a rhinovirus gets by one of the body's first line of defenses, mucus. Mucus is produced in the nose and throat and its function is to trap things we breathe in, pollen, dust, bacteria, and viruses. Unfortunately, mucus does not trap all viruses successfully.

Rhinoviruses are small , a typical lab microscope, (i.e. a light microscope), is not powerful enough to see a virus. To see a virus an electron microscope is required. Rhinoviruses are in the range of 20 - 40 nanometers in diameter, (1 nanometer = .000000001 meters). Seven to Nine billion of these bugs could fit onto the head of a pin!

Viruses are not living things. They are, however, highly infectious. Only 30 or so rhinoviruses are sufficient to cause someone to catch a cold. Because viruses are not alive they need a living host to reproduce. Viruses are parasites.

Once the virus gets into the nasal passage it travels into the adenoid area of the nose. The virus then attaches to a receptor on the surface of nasal cells. Once attached to a nasal cell, (this is called "docking"), it invades the cell highjacking the cell's replicating machinery.

A SIMPLE LESSON IN BIOLOGY: REPLICATING RHINOVIRUSES

According to certain studies a cell's replicating machinery requires at least 300 different genes to make copies of itself. Genes are found along the string of DNA contained in a cell's nucleus. Under normal conditions when a cell prepares to divide enzymes called, "polymerase", locate the positions of the genes along a string of DNA required for replication.

A vital step in the replication process is during what is called, "transcription", the polymerase identifies the starting location of the gene, the double stranded DNA unzips and a single strand of the DNA is copied to what is called mRNA, (messenger RNA). The mRNA is then used to create specialized proteins used to continue the replication process. A virus has the ability to block this functionality stopping a cell from using its own DNA for replication.

Once inside a cell the rhinovirus's RNA is exposed to the cell's replicating mechanism and because the virus releases chemicals blocking the cell's normal replicating process, the cell is "fooled" into using the RNA of the rhinovirus. The cell continues on its merry way replicating proteins only the proteins being created are components of the virus. As components of the complete virus are created they begin assembling inside the cell. The cell dies, rupturing and releasing the newly replicated virus into the host's system. The virus floats around finding, docking with, and infecting other cells. The virus multiplies exponentially as it infects more and more cells.

THE BODY FIGHTS BACK!

Cold symptoms are not caused by the virus infecting the cells, but instead, by the body's immune system as it attacks and kills the invading virus.

As the virus count increases and more cells die chemicals are released initiating an immune response. Inflammation and swelling resulting from the released chemicals attract infection fighting white blood cells. The attacking white blood cells cause more inflammation causing the infected area to become swollen and red. Tissue and small blodd vessels, (capillaries), dilate causing more white blood cells to flood the area. This activity of fighting the cold causes the cold symptoms: an increase in mucus, possibly a raised body temperature, a runny nose, sneezing, and possibly coughing.

Eventually, typically after 7 days or so, the body's immune system succeeds at preventing further cell infection by the rhinovirus while destroying all of the virus floating around in the body curing the common cold.

Remember...Wash your hands often!!