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Viruses are by far the most abundant biological entities on Earth and they outnumber all the others put together. [ 89 ] 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.
Gamma phage, an example of virus particles (visualised by electron microscopy) Virology is the scientific study of biological viruses.It is a subfield of microbiology that focuses on their detection, structure, classification and evolution, their methods of infection and exploitation of host cells for reproduction, their interaction with host organism physiology and immunity, the diseases they ...
Germ theory of disease. Scanning electron microscope image of Vibrio cholerae, the bacterium that causes cholera. The germ theory of disease is the currently accepted scientific theory for many diseases. It states that microorganisms known as pathogens or "germs" can cause disease. These small organisms, which are too small to be seen without ...
A virus is a tiny infectious agent that reproduces inside the cells of living hosts. When infected, the host cell is forced to rapidly produce thousands of identical copies of the original virus. Unlike most living things, viruses do not have cells that divide; new viruses assemble in the infected host cell. But unlike simpler infectious agents ...
Viral disease. A viral disease (or viral infection) occurs when an organism's body is invaded by pathogenic viruses, and infectious virus particles (virions) attach to and enter susceptible cells. [1] Examples are the common cold, gastroenteritis and pneumonia. [2]
Disease. A disease is a particular abnormal condition that adversely affects the structure or function of all or part of an organism and is not immediately due to any external injury. [1][2] Diseases are often known to be medical conditions that are associated with specific signs and symptoms.
An infectious disease, also known as a transmissible disease or communicable disease, is an illness resulting from an infection. Infections can be caused by a wide range of pathogens, most prominently bacteria and viruses. [2] Hosts can fight infections using their immune systems.
t. e. Severe acute respiratory syndrome coronavirus 2 (SARS‑CoV‑2) [2] is a strain of coronavirus that causes COVID-19, the respiratory illness responsible for the COVID-19 pandemic. [3] The virus previously had the provisional name 2019 novel coronavirus (2019-nCoV), [4][5][6][7] and has also been called human coronavirus 2019 (HCoV-19 or ...