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the Chain of Infection - Coggle Diagram
the Chain of Infection
Infectious Agent
Viruses - such as Influenza A, shingles and Hepatitis
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Parasitic protozoan diseases - such as Malaria, Giardia and Toxoplasmosis
Prions - which are the cause of rare progressive neurodegenrative disorders such as Creutzfeldt-Jakob disease (CJD)
The reservoir
Human reservoirs
In humans, there are two forms of reservoir: acute clinical cases (in which someone is infected and is displaying signs and symptoms of the disease); and carriers (where someone has been colonised with an infectious agent but is not unwell.
Animal & insect reservoirs
Examples of animal or insect reservoirs include Lyme disease (which is transmitted via ticks); Rabies (which is transmitted by dogs, cats, foxes and bats); and Salmonella (which is transmitted by poultry, cattle, sheep and pigs).
Environmental reservoirs
The environment contains a large number of reservoirs of infection, including soil (which acts as a reservoir for Clostridium tetani, the causative agent of tetanus) and water (which is a reservoir for Legionella pneumophila, the causative agent of Legionnaire's disease.)
The portal of exit
Alimentary - via vomiting, diarrhoea or biting
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Respiratory - through coughing, sneezing and talking
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The mode of transmission
The two main ways that an infection can be transmitted from
its reservoir to a susceptible host are via direct
transmission or indirect transmission.
Direct transmission tends to be instantaneous
and occurs when there is direct contact with the infectious agent.Examples include tetanus, glandular fever, respiratory diseases and sexually transmitted diseases.
Indirect transmission can occur through animate mechanisms such as fleas,
ticks, flies or mosquitoes or via inanimate mechanisms such as food,
water, biological products or surgical instruments.
Indirect transmission can also be airborne, in which tiny particles
of an infectious agent are carried by dust or
droplets in the air and inhaled into the lungs.
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The susceptible host
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General resistance factors (such as mucous membranes, skin, cough reflex etc) that can help defend against infection