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A virus is a submicroscopic infectious agent that replicates only inside the living cells of an organism. [1] Viruses infect all life forms, from animals and plants to microorganisms, including bacteria and archaea. [2] [3] Viruses are found in almost every ecosystem on Earth and are the most numerous type of biological entity.
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 include the common cold , gastroenteritis , COVID-19 , the flu , and rabies .
Widespread non-communicable diseases such as cardiovascular disease and cancer are not included. An epidemic is the rapid spread of disease to a large number of people in a given population within a short period of time; in meningococcal infections , an attack rate in excess of 15 cases per 100,000 people for two consecutive weeks is considered ...
Medications are usually not needed as hand, foot, and mouth disease is a viral disease that typically resolves on its own. Under research [15] [16] Sin Nombre virus: Hantavirus Pulmonary Syndrome (HPS) No Heartland virus: Heartland virus disease No Helicobacter pylori: Helicobacter pylori infection No Escherichia coliO157:H7, O111 and O104:H4
Common human diseases caused by viruses include the common cold, influenza, chickenpox and cold sores. Serious diseases such as Ebola and AIDS are also caused by viruses. [50] Many viruses cause little or no disease and are said to be "benign". The more harmful viruses are described as virulent. [51]
Also called silent disease, silent stage, or asymptomatic disease. This is a stage in some diseases before the symptoms are first noted. [23] Terminal phase If a person will die soon from a disease, regardless of whether that disease typically causes death, then the stage between the earlier disease process and active dying is the terminal phase.
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 ...
Human infectious diseases may be characterized by their case fatality rate (CFR), the proportion of people diagnosed with a disease who die from it (cf. mortality rate).It should not be confused with the infection fatality rate (IFR), the estimated proportion of people infected by a disease-causing agent, including asymptomatic and undiagnosed infections, who die from the disease.