Table of Contents1.1Introduction1.2Methodology2.0 What is a Pathogen?2.1 Main Categories of Pathogens/Microorganisms2.2 BacteriaFig. 2.3 Bacterial forms2.4 VirusesFig. 2.5 Structure of a virus2.6 Fungi2.7 Parasites3.0 Pathogenic environment4.0 What is disease?4.1 How disease spreads5.0 ConclusionReferencesPathogens and spread of disease1.1Introduction“Health depends on maintaining the internal harmony of the body. » (The U205 course team, 1985) Health is a momentary state of physical and mental well-being. This is constantly compromised by the threat of disease. It is often difficult to define exactly what a disease is, but it is generally conceived as any undesirable physical or mental condition that causes an organism to alter its normal state of existence (Nesse, 2000).1.2 MethodologyOur concern is to discuss and explore the abnormal functions and pathological structures that cause disease. To do this, we need to ask a few questions. First of all, we need to discuss what a disease is and why it occurs; we must then think about the definition of pathogens and the main categories of microorganisms and their microbial environment. Additionally, we will analyze the pathogenesis of infection, which deals with how the disease spreads and the role pathogens play in its progression. 2.0 What is a pathogen? Diseases in all humans, plants, and other organisms are caused by microorganisms called pathogens; these may include micro-organisms such as bacteria, viruses, fungi, helminths and protozoa (Inglis, 1996). The term pathogenic is most commonly used to describe an infectious organism w...... middle of article......2009]Nesse,R,D, 2000, On the difficulty of defining disease, originating from: http: //www.health.sa.gov.au/PEHS/Youve-got-what/ways-disease-spread-06.pdf, accessed [09/11/09]Peterson, RKD 1995. Insects, diseases and military history: the Napoleonic campaigns and historical perception. American Entomologist 41:147-160 Quinn, C, http://www.fungi4schools.org/Documentation/03World-of-Fungi/WF05_Fungi_and_Disease.pdf charlotte, accessed 06/11/2009 [Department of Health] 2005, from; http://www.health.sa.gov.au/PEHS/Youve-got-what/ways-disease-spread-06.pdf, accessed 7/11/2009] Wastewater Microbiology Series published online : January 28, 2005 Author(s): Michael H. Gerardi, Mel C. Zimmerma Series Editor(s): Michael H. GerardiPrint ISBN: 9780471206927 Online ISBN: 9780471710431 Copyright © 2005 John Wiley & Sons, Inc.