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Infectious disease – illness or disorder when pathogenic (disease-causing) microorganisms, such as bacteria, viruses, fungi, or parasites invade and multiply within the body of a host organism and release toxins, causing various clinical symptoms which can potentially lead to severe health complications or even death. Infectious diseases can ...
A representation by Robert Seymour of the cholera epidemic depicts the spread of the disease in the form of poisonous air.. The miasma theory was the predominant theory of disease transmission before the germ theory took hold towards the end of the 19th century; it is no longer accepted as a correct explanation for disease by the scientific community.
Epidemiology has its limits at the point where an inference is made that the relationship between an agent and a disease is causal (general causation) and where the magnitude of excess risk attributed to the agent has been determined; that is, epidemiology addresses whether an agent can cause disease, not whether an agent did cause a specific ...
Diseases caused by helminths are sometimes termed infestations, but are sometimes called infections. Arthropods such as ticks, mites, fleas, and lice, can also cause human disease, which conceptually are similar to infections, but invasion of a human or animal body by these macroparasites is usually termed infestation.
Epidemiology, the study of the patterns, causes, and effects of health and disease conditions in populations, is an important part of medical microbiology, although the clinical aspect of the field primarily focuses on the presence and growth of microbial infections in individuals, their effects on the human body, and the methods of treating ...
A zoonosis is an infectious disease of humans caused by a pathogen that can jump from a non-human host to a human. [35] Major diseases such as Ebola virus disease and salmonellosis are zoonoses. HIV was a zoonotic disease transmitted to humans in the early part of the 20th century, though it has now evolved into a separate human-only disease. [36]
In some cases, microorganisms that are not readily spread from person to person play a role, while other diseases can be prevented or ameliorated with appropriate nutrition or other lifestyle changes. Some diseases, such as most (but not all) forms of cancer, heart disease, and mental disorders, are non-infectious diseases.
Vibrio cholerae bacteria are transmitted through contaminated water. [10] Once ingested, the bacteria colonize the intestinal tract of the host and produce a toxin which causes body fluids to flow across the lining of the intestine. Death can result in 2–3 hours from dehydration if no treatment is provided. [11]