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1. Lack of animal models: Experimental infection in animals has been used as a criterion to demonstrate a disease-causing ability, but for some pathogens (such as Vibrio cholerae, which causes disease only in humans), animal models do not exist. In cases where animal models were not available, scientists have sometimes infected themselves or ...
Bacteria are prokaryotic microorganisms that can either have a bacilli, spirilli, or cocci shape and measure between 0.5-20 micrometers. They were one of the first living cells to evolve [9] and have spread to inhabit a variety of different habitats including hydrothermal vents, glacial rocks, and other organisms.
Evolution of Infectious Disease is a 1993 book by the evolutionary biologist Paul W. Ewald. In this book, Ewald contests the traditional view that parasites should evolve toward benign coexistence with their hosts. He draws on various studies that contradict this dogma and asserts his theory based on fundamental evolutionary principles.
Host–parasite coevolution is a special case of coevolution, where a host and a parasite continually adapt to each other. This can create an evolutionary arms race between them. A more benign possibility is of an evolutionary trade-off between transmission and virulence in the parasite, as if it kills its host too quickly, the parasite will ...
Stupendemys appears in the fossil record as the largest freshwater turtle, first modern elephants, giraffes, zebras, lions, rhinoceros and gazelles appear in the fossil record 3.6 Ma Blue whales grow to modern size. 3 Ma Earliest swordfish. 2.7 Ma Paranthropus evolves. 2.5 Ma Earliest species of Arctodus and Smilodon evolve. 2 Ma
A fish parasite, the isopod Cymothoa exigua, replacing the tongue of a Lithognathus. Parasitism is a close relationship between species, where one organism, the parasite, lives (at least some of the time) on or inside another organism, the host, causing it some harm, and is adapted structurally to this way of life. [1]
The disaster of the contagious disease, which changes a living being into a corpse, is caused by the infectious [nature] of the nine [kinds of] parasites (ch'ung 蟲). It is also caused by overworking one's mind and exhausting one's energy, injuring one's ch'i and loosening one's sperm—all of which happen to common folk.
Like archaea, bacteria are prokaryotic – unicellular, and having no cell nucleus or other membrane-bound organelle. Bacteria are microscopic, with a few extremely rare exceptions, such as Thiomargarita namibiensis. [53] Bacteria function and reproduce as individual cells, but they can often aggregate in multicellular colonies. [54]