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Virulence is a pathogen's or microorganism's ability to cause damage to a host. In most cases, especially in animal systems, virulence refers to the degree of damage caused by a microbe to its host. [1] The pathogenicity of an organism—its ability to cause disease—is determined by its virulence factors.
Although the vast majority of bacteria are harmless or beneficial to one's body, a few pathogenic bacteria can cause infectious diseases. The most common bacterial disease is tuberculosis , caused by the bacterium Mycobacterium tuberculosis , which affects about 2 million people mostly in sub-Saharan Africa.
The discovery of microorganisms such as Euglena that did not fit into either the animal or plant kingdoms, since they were photosynthetic like plants, but motile like animals, led to the naming of a third kingdom in the 1860s. In 1860 John Hogg called this the Protoctista, and in 1866 Ernst Haeckel named it the Protista. [20] [21] [22]
Most of the bacteria in and on the body are harmless or rendered so by the protective effects of the immune system, and many are beneficial, [4] particularly the ones in the gut. However, several species of bacteria are pathogenic and cause infectious diseases, including cholera, syphilis, anthrax, leprosy, tuberculosis, tetanus and bubonic plague.
They infect all types of cellular life including animals, plants, bacteria and fungi. [6]: 49 Different types of viruses can infect only a limited range of hosts and many are species-specific. Some, such as smallpox virus for example, can infect only one species—in this case humans, [13]: 643 and are said to have a narrow host range. Other ...
Pathogenic bacteria are bacteria that can cause disease. [1] This article focuses on the bacteria that are pathogenic to humans. Most species of bacteria are harmless and many are beneficial but others can cause infectious diseases. The number of these pathogenic species in humans is estimated to be fewer than a hundred. [2]
Plants can play host to a wide range of pathogen types, including viruses, bacteria, fungi, nematodes, and even other plants. [35] Notable plant viruses include the papaya ringspot virus , which has caused millions of dollars of damage to farmers in Hawaii and Southeast Asia, [ 36 ] and the tobacco mosaic virus which caused scientist Martinus ...
While tetanus toxin is produced from Clostridium tetani, a spore forming bacteria found in soil, Tetanus is a paralytic disease that is global and commonly affects newborns as well as non-immunized individuals. Tetanus enters the body of organisms through wounds or skin breaks and can be found in manure, soil, and dust.