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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.
The germ theory was not yet established (Louis Pasteur proposed it in 1861). Snow did not understand the mechanism by which disease was transmitted, but the evidence led him to believe that it was not foul air. Based on the pattern of illness among residents, he hypothesized that cholera was spread by an agent in contaminated water. [7]
An infectious disease agent can be transmitted in two ways: as horizontal disease agent transmission from one individual to another in the same generation (peers in the same age group) [3] by either direct contact (licking, touching, biting), or indirect contact through air – cough or sneeze (vectors or fomites that allow the transmission of the agent causing the disease without physical ...
Food chain in a Swedish lake. Osprey feed on northern pike, which in turn feed on perch which eat bleak which eat crustaceans.. A food chain is a linear network of links in a food web, often starting with an autotroph (such as grass or algae), also called a producer, and typically ending at an apex predator (such as grizzly bears or killer whales), detritivore (such as earthworms and woodlice ...
There are two major food chains: The primary food chain is the energy coming from autotrophs and passed on to the consumers; and the second major food chain is when carnivores eat the herbivores or decomposers that consume the autotrophic energy. [16] Consumers are broken down into primary consumers, secondary consumers and tertiary consumers.
Graunt's analysis of causes of death is considered the beginning of the "theory of competing risks" which according to Daley and Gani [1] is "a theory that is now well established among modern epidemiologists". The earliest account of mathematical modelling of spread of disease was carried out in 1760 by Daniel Bernoulli.
This began the path to germ specificity within the theory. [49] Louis Pasteur's contemporary Robert Koch devoted much of his scientific study to discovering certain pathogens and connecting them to specific diseases. These scientists were often in competition with one another and so the Koch-Pasteur rivalry is a well-known part of germ theory's ...
Most outcomes, whether disease or death, are caused by a chain or web consisting of many component causes. [54] Causes can be distinguished as necessary, sufficient or probabilistic conditions. If a necessary condition can be identified and controlled (e.g., antibodies to a disease agent, energy in an injury), the harmful outcome can be avoided ...