Viruses are small living organisms that are responsible for more suffering and disability than almost anything I can think of. They cause most of the childhood diseases such as measles, mumps, roseola and chickenpox. Contrary to common belief, you only get a specific virus once and then you have lifelong immunity to that specific virus. There are exceptions, but they are so rare as to not be clinically significant.
Types of Viruses
The most common types of viruses are the "cold" viruses of which there are about 130 different types. The most common species is the Rhinovirus. There are about 60 different strains of this virus which cause symptoms of the common cold. Usually these infections are not very serious and may just cause a runny nose and malaise for a couple of days. Once you get several different strains of Rhinovirus, the subsequent infections are usually not as severe since immunity to one type of Rhinovirus gives a slight advantage when the body tries to fight off another similar strain of Rhinovirus. After you get a Rhinovirus infection, you have lifelong immunity(protection) to that particular stain. Since there are 60 different strains of Rhinovirus, it can take several years to gain immunity to the majority of strains. Another common type of virus is the adenovirus. There are about 15 or so different types which cause a runny nose along with a cough and seven days or so of feeling fairly bad compared to the Rhinovirus infection. Other types of viruses are Coxsackie virus, Respiratory Syncytial virus and Echovirus. They cause the usual cold-like symptoms with congestion, sore throat, cough, fever and muscle aches. It takes several years for an infant to gain immunity to the majority of these organisms.
Spread of Viruses
Viruses are spread by contact with infected individuals. Some viruses may live for a few minutes on a glass or another object, but the usual method of spread is person-to-person contact through the mucous secretions. It is easy to see how infants and toddlers can spread the organisms to their playmates. Adults have a tendency to kiss infants which can spread the germ.
Have you ever wondered why we don't get several viruses at the same time? Our immunity tends to be low when we are sick, but we still seem to only get one cold at a time. This is because the virus produces a protein that inhibits infection by any other virus you may come in contact with. This protein is called interferon and is being used as a treatment for several diseases. Unfortunately, we have not been able to produce a medicinal form that can be used to prevent colds. Even if this was developed there is a good argument against using it on everybody because before long, nobody would have immunity to any viruses.
Common Myths about Colds
Cold weather doesn't cause a cold as we were always told when we were children. It is possible that exposure to cold weather may hamper the immune function of the respiratory system, but if there is no exposure to a virus, then it is virtually impossible to get a cold.
The Newborn Advantage
Fortunately, we have temporary immunity to most viruses when we are born.This is because immunity is passed from your mother through the placenta. It lasts for about two or three months in most cases, but up to 12 months with some viruses such as measles. Immunity is conferred through antibodies (small proteins in the blood) which are capable of destroying the viral particles. The protective proteins are gradually eliminated from the blood and the infant is no longer protected. Breast milk contains antibodies, so breast fed infants may have slightly longer protection from viruses.
Frequency of Viral Infections
The first cold will usually occur around three or four months of age if the infant is exposed to other infants that have colds. If infants stay at home for the first five years of life and have no exposure, they will not get any colds. This can actually be undesirable because the child will be exposed to numerous viruses when they start going to school. They will develop the same pattern of infection as infants who will usually get between 10 and 15 colds per year in their first two years of exposure. Children can miss so much school, that they end up having to repeat the first year. Certainly it is better to start exposure after the infant is several years old, but in today's society, frequently, both the mother and father are working and the infant has to go to a day care center. The frequency of colds per year is directly proportional to the number of children in the day care center. If there are over 10 children, the infant will get about 15 colds per year. If there are only about two or three children, then the infant may only get 10 colds per year. The infant is not susceptible to another virus for 2 weeks after the onset of one virus, because of the production of interferon. Adults will usually only get one to three colds per year unless they are smokers, in which case they may get more frequent colds.
There is no treatment for the common cold. It will last for about five to 10 days, but it varies from infant to infant. Some parents report that their child rarely got sick in spite of frequent exposure. Studies have shown that these children have protection to most viruses even though they seemingly never manifested any symptoms of infections. They actually got the usual infections, but may have only had a minimal runny nose for several hours which went unnoticed, or they possibly really didn't have any significant symptoms. When an infection occurs without any symptoms, it is called a subclinical infection and results in the same immunity as the child that gets very ill. Antibiotics will not alter the course of a viral infection. Antibiotics will help if you develop a secondary bacterial infection. This can occur frequently in some people. The most common secondary infections are a sinus infection(sinusitis), an ear infection(otitis media) and bronchitis. Ear infections and sinus infections are the most common secondary bacterial infections in infants and bronchitis is most common in smokers. Occasionally, a viral infection may be complicated by pneumonia. Treatment with antibiotics when the infection is purely viral, can actually do more harm than good. This is because the bacteria that are normally present in the body, may develop resistance to the antibiotic that is taken inappropriately. This resistant strain can then cause an infection of its own which will be unresponsive to the usual antibiotics. These resistant strains may also pass their resistance to other bacteria that infect an individual. On the other hand, it is helpful to treat with antibiotics if there is evidence of a secondary bacterial infection. Signs of secondary bacterial infections are a persistent yellow or greenish nasal drainage with or without facial pain, coughing up yellow or greenish mucous or persistant ear pain. The best thing a person can do when he or she has a cold, is to get plenty of sleep, avoid stress and drink plenty of fluids. Tylenol is helpful for the discomfort. Decongestants and antihistamines may provide some relief of symptoms, but do not shorten the time of the illness.
There are several viruses that can actually be treated with antiviral therapy. Influenza A can be treated with a medicine called amantidine. This antiviral agent has to be given within 48 hours of the onset of the flu and the sooner the better. Amantidine will not work with any other viruses. Chickenpox can now be treated with an antiviral agent called acyclovir. This medicine is more effective if given within the first day or so of the onset of the disease. Besides these examples, there are rarely any medicines that appreciably alter the course of a viral illness. Research continues in this area, but for now we will have to suffer through colds produced by these pesky little germs.
The information provided above is offered as a community service about health-care issues and is not a substitute for individual consultation. Advice on individual problems should be obtained from your personal physician. This information is based on research by the author and represents his interpretation of the literature.
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