Pathogen transmission
In
- μm.
- droplet transmission – small and usually wet particles that stay in the air for a short period of time. Contamination usually occurs in the presence of the host. Particle size > 5 μm.
- direct physical contact – touching an infected individual, including sexual contact
- indirect physical contact – usually by touching a contaminated surface, including soil (fomite)
- fecal–oral transmission – usually from unwashed hands, contaminated food or water sources due to lack of sanitation and hygiene, an important transmission route in pediatrics, veterinary medicine and developing countries.
- via contaminated hypodermic needles or blood products
Transmission can also be indirect, via another
An
The term
Transmissibility is the probability of an infection, given a contact between an infected host and a noninfected host.[7]
Community transmission means that the source of infection for the spread of an illness is unknown or a link in terms of contacts between patients and other people is missing. It refers to the difficulty in grasping the epidemiological link in the community beyond confirmed cases.[8][9][10]
Local transmission means that the source of the infection has been identified within the reporting location (such as within a country, region or city).[11]
Routes of transmission
The route of transmission is important to
Airborne infection
"Airborne transmission refers to infectious agents that are spread via droplet nuclei (residue from evaporated droplets) containing infective microorganisms. These organisms can survive outside the body and remain suspended in the air for long periods of time. They infect others via the upper and lower respiratory tracts."[12] The size of the particles for airborne infections need to be < 5 μm.[13] It includes both dry and wet aerosols and thus requires usually higher levels of isolation since it can stay suspended in the air for longer periods of time. i.e., separate ventilation systems or negative pressure environments are needed to avoid general contamination. e.g., tuberculosis, chickenpox, measles.[citation needed]
Droplet infection
A common form of transmission is by way of respiratory droplets, generated by
Organisms spread by droplet transmission include respiratory viruses such as
Direct contact
Direct contact occurs through skin-to-skin contact, kissing, and sexual intercourse. Direct contact also refers to contact with soil or vegetation harboring infectious organisms.[17] Additionally, while fecal–oral transmission is primarily considered an indirect contact route, direct contact can also result in transmission through feces.[18][19]
Diseases that can be transmitted by direct contact are called contagious (contagious is not the same as infectious; although all
Some diseases that are transmissible by direct contact include athlete's foot, impetigo, syphilis, warts, and conjunctivitis.[20]
Sexual
This refers to any infection that can be caught during sexual activity with another person, including
Some infections transmissible by the sexual route include
]Oral sex
Sexually transmitted infections such as HIV and hepatitis B are thought to not normally be transmitted through mouth-to-mouth contact, although it is possible to transmit some STIs between the genitals and the mouth, during oral sex. In the case of HIV, this possibility has been established. It is also responsible for the increased incidence of herpes simplex virus 1 (which is usually responsible for oral infections) in genital infections and the increased incidence of the type 2 virus (more common genitally) in oral infections.[citation needed]
Manual sex
While rare in regards to this sexual practice, some infections that can spread via manual sex include HPV, chlamydia, and syphilis.[21]
Oral
Infections that are transmitted primarily by oral means may be caught through direct oral contact such as kissing, or by indirect contact such as by sharing a drinking glass or a cigarette. Infections that are known to be transmissible by kissing or by other direct or indirect oral contact include all of the infections transmissible by droplet contact and (at least) all forms of herpes viruses, namely Cytomegalovirus infections herpes simplex virus (especially HSV-1) and infectious mononucleosis. [citation needed]
Mother-to-child transmission
This is from mother to child (more rarely father to child), often in utero, during
Iatrogenic
Transmission
Needle sharing
This is the practice of intravenous drug-users by which a needle or
Indirect contact
Indirect contact transmission, also known as vehicle-borne transmission, involves transmission through contamination of inanimate objects. Vehicles that may indirectly transmit an infectious agent include food, water, biologic products such as blood, and fomites such as handkerchiefs, bedding, or surgical scalpels. A vehicle may passively carry a pathogen, as in the case of food or water may carrying hepatitis A virus. Alternatively, the vehicle may provide an environment in which the agent grows, multiplies, or produces toxin, such as improperly canned foods provide an environment that supports production of botulinum toxin by Clostridium botulinum.[17]
Transmission by other organisms
A
Vectors may be mechanical or biological. A mechanical vector picks up an infectious agent on the outside of its body and transmits it in a passive manner. An example of a mechanical vector is a housefly, which lands on cow dung, contaminating its appendages with bacteria from the feces, and then lands on food prior to consumption. The pathogen never enters the body of the fly. In contrast, biological vectors harbor pathogens within their bodies and deliver pathogens to new hosts in an active manner, usually a bite. Biological vectors are often responsible for serious blood-borne diseases, such as malaria, viral encephalitis, Chagas disease, Lyme disease and African sleeping sickness. Biological vectors are usually, though not exclusively, arthropods, such as mosquitoes, ticks, fleas and lice. Vectors are often required in the life cycle of a pathogen. A common strategy used to control vector-borne infectious diseases is to interrupt the life cycle of a pathogen by killing the vector.[citation needed]
Fecal–oral
In the fecal-oral route,
Main causes of fecal–oral disease transmission include lack of adequate sanitation and poor hygiene practices - which can take various forms. Fecal oral transmission can be via foodstuffs or water that has become contaminated. This can happen when people do not adequately wash their hands after using the toilet and before preparing food or tending to patients.[citation needed]
The fecal-oral route of transmission can be a public health risk for people in
Even in developed countries there are periodic system failures resulting in a
Tracking
Tracking the transmission of infectious diseases is called
For diseases transmitted within an institution, such as a hospital, prison, nursing home, boarding school, orphanage, refugee camp, etc.,
Because these traditional methods are slow, time-consuming, and labor-intensive,
Computer simulations of infectious disease spread have been used.[32] Human aggregation can drive transmission,
Relationship with virulence and survival
Pathogens must have a way to be transmitted from one host to another to ensure their species' survival. Infectious agents are generally specialized for a particular method of transmission. Taking an example from the respiratory route, from an evolutionary perspective viruses or bacteria that cause their host to develop coughing and sneezing symptoms have a great survival advantage, as they are much more likely to be ejected from one host and carried to another. This is also the reason that many microorganisms cause diarrhea.[citation needed]
The relationship between virulence and transmission is complex and has important consequences for the long term evolution of a pathogen. Since it takes many generations for a microbe and a new host species to co-evolve, an emerging pathogen may hit its earliest victims especially hard. It is usually in the first wave of a new disease that death rates are highest. If a disease is rapidly fatal, the host may die before the microbe can be passed along to another host. However, this cost may be overwhelmed by the short-term benefit of higher infectiousness if transmission is linked to virulence, as it is for instance in the case of cholera (the explosive diarrhea aids the bacterium in finding new hosts) or many respiratory infections (sneezing and coughing create infectious aerosols).[citation needed]
Anything that reduces the rate of transmission of an infection carries positive externalities, which are benefits to society that are not reflected in a price to a consumer. This is recognized implicitly when vaccines are offered for free or at a cost to the patient less than the purchase price.[34]
Beneficial microorganisms
The mode of transmission is also an important aspect of the biology of beneficial microbial symbionts, such as
Vertical transmission
Horizontal transmission
Some beneficial symbionts are acquired horizontally, from the environment or unrelated individuals. This requires that host and symbiont have some method of recognizing each other or each other's products or services. Often, horizontally acquired symbionts are relevant to secondary rather than primary metabolism, for example for use in defense against pathogens,[36] but some primary nutritional symbionts are also horizontally (environmentally) acquired.[37] Additional examples of horizontally transmitted beneficial symbionts include bioluminescent bacteria associated with bobtail squid and nitrogen-fixing bacteria in plants.[citation needed]
Mixed-mode transmission
Many microbial symbionts, including
See also
- Bioaerosol
- Bugchasing
- Cross-species transmission
- Infectious disease: Transmission
- Transmission coefficient (epidemiology)
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