In 1330, an outbreak of the deadly bubonic plague broke out in China. Because of China’s importance as a trading nation the plague quickly spread to Western Asia and Europe. In October 1347, several Italian merchant ships returned from the Baltic Sea, one of the trade links with China. When the ship docked in Sicily there were already dead and dying on board. The plague rapidly spread to the city. When the population discovered what had happened, the sailors were driven out, but it was too late. By August the following year it had spread to England and in the next five years an estimated 25 million people died. It was called the Black Death because the infection, which progressed with lightning speed, caused spots on the skin that were red at first and then turned black.
The bubonic plague was caused by the bacteria Yersinia pestis, a single- celled organism that infected humans and rats. It was spread by fleas. Other diseases caused by bacteria include pneumonia, tuberculosis, typhoid fever and salmonella food poisoning. The spread of these infections is often due to overcrowding and poor hygiene. Since the discovery of penicillin by Flemming in 1929 and the later development of a variety of antibiotics, the death rate from bacterial infections has been slashed and the threat of plagues largely been eliminated.
But another type of disease-causing organism is the virus. These tiny organisms, much smaller than bacteria, are made of a single strand of genetic material encased in an outer coat of protein and in some cases a layer of fat.
They cannot reproduce themselves and are totally dependent on being reproduced in the cells they infect. Viruses are the active agents in infections such as polio, measles, the common cold and influenza.
Viral infections cannot be treated with antibiotics. But once a person has had a viral infection they do not usually get the illness a second time.
The immune system develops protection against the specific virus although infection may recur if is dealt with rapidly and there are no obvious symptoms.
Protection against viruses can be provided by vaccination. The discovery of vaccines dates back to the classic experiment in 1798 of Edward Jenner, an English country doctor, although the principle of vaccination had been used by ancient civilisations for centuries before.
Vaccines began to be widely used in the late 1800s and early 1900s. Vaccines have had one of the greatest impacts on the world’s health and today diseases that were once worldwide are no longer a threat. For example, smallpox was a highly contagious and often fatal disease that has virtually been eradicated by a massive worldwide vaccination program during the past century. The last recorded case was in Somalia in 1977. Vaccines are equally successful against bacterial infections.
The problem facing us now is the possibility of “super bugs” resistant to antibiotics, or virus strains for which there are no vaccines available, such as the common cold and some strains of the flu.
In this situation we have to rely totally on the body’s defence mechanism. Our immune system is comprised of millions of white cells that circulate in the blood and through the tissues. There are different types of white cells with highly specialised functions. They have the ability to identify bacteria, viruses, and cells that have become cancerous, and to seek out and destroy these cells.
Our resistance to infection and the outcome of an infection will depend on the ability of the white cells to destroy the infective organism before it disables some vital function or organ in the body.
A major player in the immune system is the killer cell (T ‑ lymphocyte). It is the one that carries out the destruction of bacteria, viruses and cancer cells. Killer cells are aided by the 13 ‑ lymphocytes that identify targets for destruction and mark them with antibody. The killer cells are able to move out of the blood vessels and roam through the tissues seeking out the targets to be destroyed.
One of the most lethal diseases to threaten humans is HIV/AIDS. This is due to a virus that attacks the killer cells, putting them out of action. When that occurs the immune system is crippled and the infected person may succumb to a simple infection that would have normally been quickly dealt with. Fortunately infection requires direct contact with the infected person, or viral ‑ infected fluids, and with the use of appropriate protection, transmission of the organism can be prevented.
Cold and flu viruses are spread by airborne transmission. Appropriate measures can reduce the risk of infection but it is not always possible to completely protect oneself.
When a virus gets into the body, it is up to the immune system to seek it out and destroy it. Fortunately there are a number of things we can do to stimulate immune function and maximise the effectiveness of the body’s defence system.
One of the worst habits we get into is pushing the limits—once called “intemperance.” Any sort of fatigue—physical, mental or emotional—will eventually depress the immune function.
Moderate physical activity is a great stimulator of the immune system, but excessive exercise will depress it and increase the likelihood of respiratorytract infections. This is the reason for the greater incidence of infection among long-distance runners. Regular activity will also help offset the decline of immune function that normally occurs with advancing years.
Sleep deprivation depresses immune function. When test subjects were deprived of sleep from 10 pm until 3 am the number, and activity, of circulating killer cells decreased. Sleep deprivation for 48 hours resulted in a similar effect.
Stress is like exercise—some is good but too much is bad. I wouldn’t want to be without the rush of adrenaline when something exciting happens or a difficult task has been achieved. Small amounts of stress stimulate immune function and spur us on to success, but if stress continues unabated then we are heading for trouble. The immune system is depressed and our defences weakened.
Dietary excess likewise has a detrimental effect on the immune system. Excess of fat or sugar or simply eating too much will depress the immune system.
No wonder colds and sore throats are so common after birthday parties, Christmas and other special occasions. In these situations there is often a high intake of fat, sugar and calories, the immune function is impaired, and it only needs one person with an infection that is readily passed on to others and the inevitable consequences of the cold or flu result.
Long-distance air travellers are particularly vulnerable to infection with the combined effects of increased exposure to infective organisms in crowded environments, fatigue from lack of sleep, lack of exercise and the stress of changing time zones.
Even what we look at has an effect on the body. Studies show that when we watch crime and violence on TV the brain fails to differentiate between the video display and reality, normal stress responses occur and the immune function decreases.
The immune system needs good nutrition.
Essential nutrients include vitamins C and E, betacarotene, zinc and selenium.
These are best obtained from foods rich in these nutrients. Good sources of vitamin C are citrus, pineapple, berries, kiwifruit and pawpaw. Betacarotene is present in orange-coloured vegetables and fruit, and in green leafy vegetables. Vitamin E is present in seeds and nuts such as sunflower seeds and almonds and in wholegrain cereals. The best source of selenium is brazil nuts—three or four of these each week will help maintain good selenium reserves.
Garlic is a food that has many beneficial effects, including enhancement of the immune function. It would be good to include it regularly in the diet.
Some substances such as zinc and echinacea are known to stimulate immune activity. These are best kept for use when needed. If used continually as a preventative, the effect may be lost. It’s like the first cup of coffee that gives a real kick but the effect wears off with continual use until a person starts to suffer withdrawal headaches that are relieved by more caffeine. Zinc tablets taken on a daily basis for a few days will stimulate killer cell activity but after 10 days continual use will depress immune function and any beneficial effect is lost.