What Is Pathogenicity?

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  • Written By: Kathy Dowling
  • Edited By: E. E. Hubbard
  • Last Modified Date: 09 October 2019
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Pathology is the study of the modification of tissues, cells, and organs within the body as a result of disease. Pathogenicity is the term applied to a pathogen that is capable of causing infectious diseases within in the body. Health issues caused by these micro-organisms include both protozoa and bacterial infections and infectious diseases. An organism’s pathogenicity is often referred to as its virulence.

All systems work together in the body in order to maintain homeostasis, or normal physiological processing. Homeostasis is the process whereby the body is able to regulate temperature, metabolism, and blood pressure despite conditions in its external environment. If the systems within the body are changed, however, a disease may occur. Pathologists study diseases in order to understand how they work and to provide treatment for them.

Pathogenesis refers to the way in which a disease begins and then develops over time. When a pathologist studies a pathogen, he or she particularly studies the cellular and physiological activities that take part in the development of the disease. The process of pathogenesis involves determining what caused the disease, the damage it has caused, and the changes that have occurred since its presence. Some micro-organisms are frequently pathogenic, or disease-producing, while others rarely cause disease. For example, the pathogenicity of opportunistic pathogens is not recurrent in people with good health, but can cause infections in people with a low immune system.


Diseases such as infections are caused by micro-organisms. These micro-organisms are pathogens and include bacteria and protozoa. The damage to the body as a result of such pathogens may be direct from destroyed tissue or it may be indirect as a result of a toxin that it produces. The pathogenicity, or virulence, of pathogens such as bacteria and protozoa is measured by pathologists and determined by the number of organisms that is needed for the disease to occur.

Bacteria are involved in many human diseases. Such infections can be minor, for example, an infected eye or ear. They can also be potentially lethal, such as tuberculosis, a condition commonly affecting the lungs and causing symptoms such as night sweats, fever, and weight loss. This type of pathogen can enter the body via the skin or orifices such as the mouth and nose. Disease is caused when the infectious bacterium produces endotoxins and exotoxins that are poisonous, resulting in tissue inflammation.

Another pathogen is protozoa, which is a primitive animal that consists of a single cell. They are larger in size than bacteria, but are still microscopic. Most live independently and are able to excrete, absorb food, and breathe; however, there are some protozoa that are parasitic and cause diseases in humans. Giardiasis is a disease caused by protozoa resulting in an intestinal infection causing diarrhea.


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