Many contagious diseases can cause the body to deteriorate. According to the U.S. National Library of Medicine and the National Institutes of Health (NIH), contagious or communicable diseases are the world's leading cause of death. The NIH states that there are four principle types of infectious agents: bacteria, viruses, fungi and protozoa. People can spread communicable diseases by touching, eating, drinking or breathing something that's been contaminated.
Tuberculosis
According to the New Jersey Medical School Global Tuberculosis Institute (GTI), a center dedicated to advancing tuberculosis care through research, practice and teaching, tuberculosis is a disease caused by the Mycobacterium tuberculosis bacteria. Although the bacteria can affect any part of a person's body, it often targets the lungs.
The GTI notes that tuberculosis was once the leading cause of death among Americans. Tuberculosis spreads through the air from one person to another. The Mycobacterium tuberculosis bacteria go into the air when an infected person coughs or sneezes. Many people who are infected with tuberculosis do not develop tuberculosis disease, as the tuberculosis bacteria can lie dormant for an entire lifetime. However, in some people, especially people with compromised immune systems, tuberculosis disease can manifest and cause the body to deteriorate.
HIV/AIDS
The National Institute of Allergy and Infectious Diseases (NIAID), a division of the NIH, states that there were 33 million people around the world living with HIV/AIDS as of 2007. HIV, or human immunodeficiency virus, causes AIDS, or acquired immunodeficiency syndrome. HIV targets a person's immune system by damaging CD4+ T cells--white blood cells that are needed to ward off infection. When a person's CD4+ T cell counts drop, he becomes vulnerable to opportunistic infections, such as pneumonia or tuberculosis, that can cause rapid physical deterioration or degeneration. According to NIAID, AIDS is the final stage of HIV infection, and the criteria for an AIDS diagnosis includes the following: the person has one or more opportunistic infections and a CD4+ T cell count under 200 cells per cubic millimeter of blood.
Influenza
According to the World Health Organization (WHO), influenza is a viral infection that targets a person's respiratory system, including her nose, throat, bronchi and lungs. The influenza virus spreads between people by droplets from an infected person when she coughs or sneezes. Common influenza-related symptoms include high fever, muscle aches, headache, malaise, non-productive cough, sore throat and sore nose. Most bouts of influenza last approximately one week and require little or no medical intervention, although some people, especially the elderly and people with compromised immune systems, can develop serious health complications associated with influenza infection, including pneumonia and death. The NIH reports that about 5 to 20 percent of Americans get the flu every year.
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