Contents1.1Introduction1.2Methodology2.0 What is a pathogen?2.1 Main categories of pathogens/microorganisms2.2 BacteriaFig 2.3 Bacterial forms2.4 VirusFig 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 the spread of disease1.1Introduction"Health depends on the body maintaining its internal harmony." (The U205 Course Team, 1985) Health is a temporary condition of one's state of physical and mental well-being. This is constantly compromised by the threat of disease. It is often difficult to define exactly what disease is, however it is generally conceived as any undesirable physical or mental condition that causes an organism to alter from its normal state of existence (Nesse, 2000).1.2 MethodologyOur concern is to discuss and explore the abnormal functions and pathological structures that underlie disease and illness. To do this we need to ask ourselves some questions. First we need to discuss what the disease is and why it occurs; it is then necessary to consider the definition of pathogens and the main categories of microorganisms and their microbial environment. We will also analyze the pathogenesis of the infection which concerns how the disease spreads and what role pathogens play in its development. 2.0 What is a pathogen? Diseases in all humans, plants, and other organisms are caused by microorganisms called pathogens; these can be microorganisms such as bacteria, viruses, fungi, helminths and protozoa (Inglis,1996). The term pathogen is most commonly used to describe an infectious organism with...... half of the document ......2009]Nesse,R,D, 2000, On the difficulty of defining disease, taken from: http: //www.health.sa.gov.au/PEHS/Youve-got-what/ways-disease-spread-06.pdf, accessed [9/11/09]Peterson, R.K.D. 1995. Insects, disease and military history: the Napoleonic campaigns and historical perception. American Entomologist 41:147-160Quinn, C, http://www.fungi4schools.org/Documentation/03World-of-Fungi/WF05_Fungi_and_Disease.pdf Charlotte, accessed [06/11/2009]How infectious diseases spread , [Department of Health] 2005, Taken 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. Gerardi Print ISBN: 9780471206927 Online ISBN: 9780471710431 Copyright © 2005 John Wiley & Sons, Inc.