WHY DO WE FALL ILL
When there is a disease, either the functioning or the appearance of one or more systems of the body will change for the worse.
These changes give rise to symptoms and signs of disease.
Diseases last for only very short periods of time, and these are called acute diseases.
For a long time, even as much as a lifetime, and are called chronic diseases.
An example is the infection causing elephantiasis, which is very common in some parts of India.
All diseases will have immediate causes and contributory causes.
Also, most diseases will have many causes, rather than one single cause.
One group of causes is the infectious agents, mostly microbes or micro-organisms.
Peptic ulcer disease is no longer a chronic, frequently disabling condition, but a disease that can be cured by a short period of treatment with antibiotics.
Staphylococci, the bacteria which can cause acne.
Trypanosoma, the protozoan organism responsible for sleeping sickness.
The organism is lying next to a saucer-shaped red blood cell to give an idea of the scale.
Leishmania, the protozoan organism that causes kala-azar.
The organisms are oval-shaped, and each has one long whip-like structure.
One organism (arrow) is dividing, while a cell of the immune system (lower right) has gripped on the two whips of the dividing organism and is sending cell processes up to eat up the organism.
The immune cell is about ten micrometres in diameter.
Common examples of diseases caused by viruses are the common cold, influenza, dengue fever and AIDS.
Diseases like typhoid fever, cholera, tuberculosis and anthrax are caused by bacteria.
Many common skin infections are caused by different kinds of fungi.
Protozoan microbes cause many familiar diseases, such as malaria and kalaazar.
Antibiotics.
They commonly block biochemical pathways important for bacteria.
Many bacteria, for example, make a cell-wall to protect themselves.
The antibiotic penicillin blocks the bacterial processes that build the cell wall.
As a result, the growing bacteria become unable to make cell-walls, and die easily.
But viruses do not use these pathways at all, and that is the reason why antibiotics do not work against viral infections.
Many microbial agents can commonly move from an affected person to someone else in a variety of ways.
In other words, they can be „communicated‟, and so are also called communicable diseases.
Examples of such diseases spread through the air are the common cold, pneumonia and tuberculosis.
The bacteria cause tuberculosis.
If they enter through the mouth, they can stay in the gut lining like typhoid causing bacteria or if they go to the liver, like the viruses that cause jaundice.
An active immune system recruits many cells to the affected tissue to kill off the disease-causing microbes. This recruitment process is called inflammation.
In HIV infection, the virus goes to the immune system and damages its function.
Thus, many of the effects of HIV-AIDS are because the body can no longer fight off the many minor infections that we face every day.
Making anti-viral medicines is harder than making antibacterial medicines is that viruses have few biochemical mechanisms of their own.
They enter our cells and use our machinery for their life processes.
There are vaccines against tetanus, diphtheria, whooping cough, measles, polio and many others.
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