Causes and Spread of Infection

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The causes of infection.
Diseases can be classified as genetic, metabolic, or infectious. Infectious diseases are caused by bacteria, viruses, fungi and parasites that use our body as a host for reproduction and cause illness. Bacteria, viruses, fungi and parasites.

These are all microorganisms which cause infection, yet they are all different in structure, required environment and conditions needed to thrive and multiply.
Bacteria is a single celled organism. It’s shape and size can vary greatly from one type of bacteria to another, but its general structure is that of a simple cellular one with a nucleus that lacks a membrane.They can thrive in almost any environment and can be found within almost any substance/surface, also within the human body. However, it is thought that only about 7% of all bacteria is actually harmful and cause diseases. These are called “pathogenic” bacteria. Pathogenic bacteria cause illness as they rapidly reproduce and produce a toxin that kills or mutilates cells. Bacteria is self sufficient, meaning that it does not rely upon other organisms to survive. Antibiotics, like penicillin, are substances that are toxic to the bacteria, but relatively harmless to people. They have been very useful in combating disease, but their increased use has produced antibiotic-resistant bacteria, which is now largely recognised as an area of concern in the health profession. One bacteria, MRSA, is responsible for many serious infections that are sometimes fatal. Bacterias which cause common illnesses includes E. Coli, which causes diarrhea, abdominal pain, and even kidney failure, Salmonella, a frequent cause of food poisoning, Vibrio cholerae, which causes cholera, and Mycobacterium tuberculosis, which is the cause of tuberculosis (TB). Viruses are pieces of nucleic acid (DNA or RNA) surrounded by a thin coat of protein that can only replicate within the walls of another living cell. They are smaller than bacteria, but are not a cell or living. Viruses replicate by invading another cell that acts as a host, replicating within these cell walls, until eventually the cell dies and multiple copies of this virus is released. They then go on to invade more body cells. The human body sometimes is able to build antibodies that prevent the replication of the virus to stop the infection. Vaccines consist of weakened viruses that stimulate the body's defenses to fight infection by the natural viruses. Common illnesses caused by viruses include the common cold (caused by a rhinovirus), Influenza, and AIDS (which is caused by the virus HIV) Fungi can include single celled yeasts which are slightly bigger than bacteria, as well as multi-celled organisms such as mushrooms and molds. However, they do not have chlorophyll to make their own food like plant do, so they get their nutrition by acting as parasites or by breaking down remains of dead plants or animals. Some fungi are poisonous, but some are beneficial. For example, one type of fungi is the source of Penicillin, and others are essential in the making of food products. Fungal diseases are called mycoses. These include Aspergillosis (infection of sinuses and lungs), Coccidioidomycosis (may cause cough, chest pain and shortness of breath), and Blastomycosis (skin and pulmonary infections). Parasites may be protozoa, but can also be fungal or multi-cellular organisms. Protozoa is a single celled organism which has a more complex cell structure than bacteria. Some protozoa are able to surround themselves with a type of cyst, which enables them to live outside of a host for a long time, but generally a parasite needs a host in order to feed. Some diseases caused by protozoans are Malaria (transmitted by mosquitoes), and amoebic dysentery (an infection of the intestine caused by Entamoeba histolytica). Multicellular parasites include various types of worm and fungi that can cause a variety of common diseases including tapeworm, ringworm and athlete's foot....
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