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Transmission can also be indirect, via another organism, either a vector (e.g. a mosquito or fly) or an intermediate host (e.g. tapeworm in pigs can be transmitted to humans who ingest improperly cooked pork). Indirect transmission could involve zoonoses or, more typically, larger pathogens like macroparasites with more complex life cycles.
The following outline is provided as an overview of and topical guide to concepts related to infectious diseases in humans.. Infection – transmission, entry/invasion after evading/overcoming defense, establishment, and replication of disease-causing microscopic organisms (pathogens) inside a host organism, and the reaction of host tissues to them and to the toxins they produce.
Main causes of fecal–oral disease transmission include lack of adequate sanitation (leading to open defecation), and poor hygiene practices. If soil or water bodies are polluted with fecal material, humans can be infected with waterborne diseases or soil-transmitted diseases. Fecal contamination of food is another form of fecal-oral transmission.
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.
There are four kinds of microorganisms that cause infectious disease: bacteria, fungi, parasites and viruses, and one type of infectious protein called prion. A medical microbiologist studies the characteristics of pathogens, their modes of transmission, mechanisms of infection and growth
Vertical transmission of symbionts is the transfer of a microbial symbiont from the parent directly to the offspring. [1] Many metazoan species carry symbiotic bacteria which play a mutualistic, commensal, or parasitic role. [1] A symbiont is acquired by a host via horizontal, vertical, or mixed transmission. [2]
Vector-borne transmission, transmitted by a vector, which is an organism that does not cause disease itself but that transmits infection by conveying pathogens from one host to another. [ 32 ] The relationship between virulence versus transmissibility is complex; with studies have shown that there were no clear relationship between the two.
Aerosol transmission has traditionally been considered distinct from transmission by droplets, but this distinction is no longer used. [ 3 ] [ 4 ] Respiratory droplets were thought to rapidly fall to the ground after emission: [ 5 ] but smaller droplets and aerosols also contain live infectious agents, and can remain in the air longer and ...