Microbiology and Immunology

Cold, viruses WORLD OF MICROBIOLOGY AND IMMUNOLOGY

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runny nose, cough, sore throat, and sneezing that advertise that

you have a cold. More than 200 viruses, each with its own

favored method of being passed from one person to another,

its own gestation period, each different from the others, wait

patiently to invade the mucous membranes that line the nose

of the next cold victim.

Passing the cold-causing virus from one person to the

next can be done by sneezing onto the person, by shaking

hands, or by an object handled by the infected person and

picked up by the next victim. Oddly, direct contact with the

infected person, as in kissing, is not an efficient way for the

virus to spread. Only in about 10% of such contacts does the

uninfected person get the virus. Walking around in a cold rain

will not cause a cold. Viruses like warm, moist surroundings,

so they thrive indoors in winter. Colds are easily passed in the

winter, because people spend more time indoors then than they

do outdoors. However, being outdoors in cold weather can

dehydrate the mucous membranes in the nose and make them

more susceptible to infection by a rhinovirus.

In addition, cold-causing viruses mutate with regularity.

Each time it is passed from one person to the next, the virus

changes slightly, so it is not the virus the first person had.

Viruses are obligate parasites, meaning that they can carry out

their functions only when they invade another living cell.

The virus has a tough envelope surrounding its nucleic

acids, the genetic material for any living thing. Once it invades

the body, the virus waits to be placed in the location in which

it can function best. Once there, it attaches to a cell by means

of receptor areas on its envelope and on the cell membrane.

The viral nucleic acid then is inserted into the cell nucleusand

it takes over the functions of the nucleus, telling it to repro-

duce viruses.

Taking regular doses of vitamin C will not ward off a

cold. However, high doses of vitamin C once a person has a

cold may help to alleviate symptoms and reduce discomfort.

Over-the-counter drugs to treat colds treat only the symptoms.

They may dry up the patient’s runny nose, but after a few days

the nose will compensate and overcome the effects of the med-

ication and begin to drip again. The runny nose is from the loss

of plasma from the blood vessels in the nose. Some researchers

assert the nose drip is a defensive mechanism to prevent the

invasion of other viruses. Antibioticssuch as penicillinare use-

less against the cold because they do not affect viruses.

Scientists agree that the old wives’ remedy of chicken

soup can help the cold victim, but so can any other hot liquid.

The steam and heat produced by soup or tea helps to liquefy the

mucus in the sinus cavities, allowing them to drain, reducing

the pressure and making the patient feel better. The remedy is

temporary and has no effect on the virus. Colds are usually

self-limiting, and recovery usually occurs within a week.

See alsoCold, viruses; Infection and resistance; Viruses and

responses to viral infection

CCold, virusesOLD, VIRUSES

The cold is one of the most common illnesses of humans. In

the Unites States alone, there are more than one billion colds

each year. Typically a cold produces sneezing, scratchy throat,

and a runny nose for one or two weeks. The causes of the com-

moncoldare viruses.

More than 200 different viruses can cause a cold.

Rhinoviruses account for anywhere from 35% to over half of

all colds, particularly in younger and older people. This has

likely been the case for millennia. Indeed, the name

Rhinovirus is from the Greek word rhin, meaning, “nose.”

There are over one hundred different types of Rhinovirus,

based on the different proteins that are on the surface of the

virus particle. Rhinovirus belongs to the virus family

Picornaviridae. The genetic material of the virus is ribonucleic

acid(RNA) and the genome is of a very small size.

Rhinovirus is spread from one person to another by “hand

to hand” contact, that is, by physical contact or from one person

sneezing close by another person. The virus needs to inside the

human body to be able to replicate. The internal temperature of

the body, which is normally between 97–99°F (36.1–37.2° C) is

perfect for Rhinovirus. If the temperature varies only a few

degrees either way of the window, the virus will not replicate.

Sneezing is a symptom of the common cold.

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