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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.
Although fecal–oral transmission is usually discussed as a route of transmission, it is actually a specification of the entry and exit portals of the pathogen, and can operate across several of the other routes of transmission. [1] Fecal–oral transmission is primarily considered as an indirect contact route through contaminated food or water.
Pathogens include bacteria, fungi, protozoa, parasitic worms (helminths), and viruses. Each of these different types of organisms can then be further classified as a pathogen based on its mode of transmission. This includes the following: food borne, airborne, waterborne, blood-borne, and vector-borne.
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.
Microorganisms carried in this manner can be dispersed widely by air currents and may become inhaled by a susceptible host within the same room or over a longer distance from the source patient, depending on environmental factors; therefore, special air-handling and ventilation are required to prevent airborne transmission. Microorganisms ...
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 ...
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]