Many human illnesses including common respiratory infections are caused by infection with either bacteria or viruses.
Bacteria
These are tiny single-celled organisms that are among the most successful life forms on our planet, as they can survive anywhere from ice fields to deserts. Some bacteria, such as gut bacteria that help you digest food, are necessary for a healthy life; others are responsible for many diseases. Many bacterial infections can be treated with antibiotics, although antibiotic-resistant strains are now appearing because we have overused this precious medicine. Immunisation is also available to prevent many bacterial diseases.
Viruses
A virus is an even tinier micro-organism that can only reproduce inside a host's living cell. It is very difficult to kill a virus. Some of the most serious communicable diseases known to medical science are viral. Many viral illnesses are also preventable by immunisation … but, unfortunately, not the common cold.
How bacteria and viruses enter the body
To cause an infection, bacteria have to get into your body. This usually happens through close contact with an infected person – directly, by breathing in droplets from coughs or sneezes, or indirectly, by touching objects that have been contaminated such as taps, pencils, drink bottles, toys and telephones, and then putting your hands on your eyes, nose or mouth.
Under the right conditions, a bacterium can outdo a rabbit: it reproduces itself so that one single bacterium can bloom into 500,000 or more bacteria within just eight hours.
Viruses are also spread from one person to another by coughs, sneezes or vomit. Viruses can exist outside a host cell, but they can't reproduce. A virus replicates its genetic material inside a host cell until that cell is so full it bursts, and the viruses pour out and invade other cells. The body finds it much harder to fight a viral infection than a bacterial infection.
Antibiotics are useless against viral infections, and scientists are working on drugs that kill viruses. There are at present effective antiviral drugs against a few viral diseases such as influenza, herpes, hepatitis B and C and HIV. Many viral infections such as measles, mumps, hepatitis A and hepatitis B are prevented with immunisation but viruses that cause the common cold mutate from one person to the next so fast that the viruses have changed their format by the time vaccines are developed.
Respiratory infections can have symptoms in common, for example fever, cough and a blocked or runny nose. You can have more than one type of infection at the same time: the infection can spread, or your weakened state can make you more likely to pick up another infection.
Good habits to stop infection spreading
Catching a cold or the flu makes you miserable and highly contagious. There is really only one way you can catch a cold or the flu and that is by a virus entering your respiratory tract. Avoiding getting infection or spreading infection means doing everything possible to stop the virus from getting into your mouth, nose or throat.
All material is © Media 21 Publishing, and originally appeared in the July 2008 issue of Good Health & Medicine magazine.
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