Clasification Essay

Infectious Diseases

Historically, infectious diseases have been affecting humanity for hundred of years and now they are the biggest killers of kids and young adults in the world producing more than thirteen millions of deaths in a year. Thirty new infectious diseases have been discovered during the last twenty years and in between those, the mortal Ebola and HIV. There are four types of infectious diseases according to the pathogenic agent that produce this kind of diseases.

Viruses cause the first type of infectious diseases and they cause sickness in every living organism. Lately, a lot of new viruses have been discovered; some of them do not affect humans or animals but some others affected considerably, through history, the human being. Virus diseases include common cold (influenza), herpes, measles, a variety of smallpox, hepatitis, AIDS, and encephalitis.

The second type is the bacterial diseases. The bacteria are a unicellular microorganism that only has a few millimeters and that has different forms. Even though the immune system makes the majority of those inoffensive or beneficial, some bacteria may cause infectious diseases: cholera, syphilis, anthrax, and leprosy between others. The most common bacterial diseases are the respiratory infections, such as tuberculosis, that have a wide range of diseases.

Parasites or parasitic diseases are the third type and they happen when parasites find in the host good enough conditions to live, to develop, to multiply and to act as a virus in order to produce a disease. Because parasites are well adapted to their kind of life, they are not easy to eradicate. They develop strategies to avoid the host's defensive mechanism and lots of them have obtained resistance to medicines and insecticides. There are two types of parasites: intern (rounds and flats) and extern (ticks, fleas, and lice)

The last infectious diseases are caused by