Attribution :"Pathogen and its Types" by Doubtnut is licensed under CC BY 3.0

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A disease is any condition in which the normal structure or functions of the body are damaged or impaired. Physical injuries or disabilities are not classified as disease, but there can be several causes for disease, including infection by a pathogen, genetics (as in many cancers or deficiencies), noninfectious environmental causes, or inappropriate immune responses. Our focus in this chapter will be on infectious diseases, although when diagnosing infectious diseases, it is always important to consider possible noninfectious causes.

Signs and Symptoms of Disease An infection is the successful colonization of a host by a microorganism. Infections can lead to disease, which causes signs and symptoms resulting in a deviation from the normal structure or functioning of the host. Microorganisms that can cause disease are known as pathogens. The signs of disease are objective and measurable, and can be directly observed by a clinician. Vital signs, which are used to measure the body’s basic functions, include body temperature (normally 37 °C [98.6 °F]), heart rate (normally 60–100 beats per minute), breathing rate (normally 12–18 breaths per minute), and blood pressure (normally between 90/60 and 120/80 mm Hg). Changes in any of the body’s vital signs may be indicative of disease. For example, having a fever (a body temperature significantly higher than 37 °C or 98.6 °F) is a sign of disease because it can be measured. In addition to changes in vital signs, other observable conditions may be considered signs of disease. For example, the presence of antibodies in a patient’s serum (the liquid portion of blood that lacks clotting factors) can be observed and measured through blood tests and, therefore, can be considered a sign.


Suggested Reading Books :  External link : https://oer.galileo.usg.edu/biology-textbooks/15/

You can Download the chapter 04 and chapter 05 using above links,

Chapter 4 Acellular Pathogens.pdf
You can learn Topics from above book:
1.Viruses and Structure
2.Classification of Viral Diseases
3.Viroids, Virusoids, and Prions


Chapter 5 Microbial Mechanisms of Pathogenicity.pdf
You can learn Topics from above book:
1.Characteristics of Infectious Disease
2.Classifications of Disease
3.How Pathogens Cause Disease