Transmission (medicine) 729317 224311252 2008-07-08T08:03:26Z Littlealien182 3345501 Repaired link to [[Wikipedia:WikiProject Disambiguation|disambiguation]] page using [[Project:AutoWikiBrowser|AWB]] In [[medicine]], '''transmission''' is the passing of a [[disease]] from an infected individual or group to a previously uninfected individual or group. The microorganisms ([[bacterium|bacteria]] and [[virus]]es) that cause disease may be transmitted from one person to another by one or more of the following means: * droplet contact - coughing or sneezing on another person * direct physical contact - touching an infected person, including sexual contact * indirect contact - usually by touching [[soil contamination]] or a contaminated surface * airborne transmission - if the microorganism can remain in the air for long periods * fecal-oral transmission - usually from contaminated food or water sources * vector borne transmission - carried by insects or other animals Microorganisms vary widely in the length of time that they can survive outside the human body, and so vary in how they are transmitted. ==Horizontal and vertical== Disease can be transmitted in two ways: *[[Horizontal disease transmission]] – from one individual to another in the same generation (peers in the same age group).<ref name = "S1">[http://www.online-medical-dictionary.org/Horizontal+Disease+Transmission.asp?q=Horizontal+Disease+Transmission Horizontal Disease Transmission], online-medical-dictionary.org</ref> Horizontal transmission can occur by either direct contact (licking, touching, biting), or indirect contact ([[Vector (biology)|vectors]] or [[fomites]] that allow the transmission of disease without physical contact).<ref name= "S2">''[http://www.vet.uga.edu/vpp/IVM/ENG/Modes/routes.htm Routes of transmission of infectious diseases agents]''</ref> *''Vertical disease transmission'' – passing a disease causing agent vertically from parent to offspring. Typically the mother transmits the disease by means of bodily fluid, and sometimes breast milk.<ref name= "S1">[http://www.medterms.com/script/main/art.asp?articlekey=7982 Vertical transmission definition - Medical Dictionary definitions of popular medical terms easily defined on MedTerms<!-- Bot generated title -->]</ref> ==Transmission, symptoms and survival== In order to survive, microorganisms must have a way to be transmitted from one host to another. Infectious agents are generally specialized for a particular method of transmission. Taking an example from the respiratory route, from an evolutionary perspective a virus or bacteria that causes its host to develop coughing and sneezing symptoms has a great survival advantage - it is much more likely to be ejected from one host and carried to another. This is also the reason that many microorganisms cause [[diarrhea]] ==Locus== In transmission, a locus is the point on the body where a pathogen enters. *In droplet contact and other airborne transmission it is generally the [[respiratory system]] *In direct physical and indirect contact it is generally through a wound in the skin or through a [[mucous membrane]] *In fecal-oral transmission, it is through the mouth. *In vector borne transmission, it is at the bite or sting of the vector. ==Routes of Transmission== ===Droplet Contact=== [[Image:Aerosol from Sneeze.jpg| thumb | right | 250px |Microorganisms (bacteria and viruses) that cause disease may be transmitted from one person to another by [[aerosol]]s created when a patient sneezes or coughs]] Also known as the ''respiratory route'', it is a typical mode of transmission among many infectious agents. If an infected person coughs or sneezes on another person the microorganisms, suspended in warm, moist droplets, may enter the body through the nose, mouth or eye surfaces. Diseases that are commonly spread by coughing or sneezing include (at least): * Bacterial [[Meningitis]] * [[Chickenpox]] * [[Acute viral nasopharyngitis (common cold)|Common cold]] * [[Influenza]] * [[Mumps]] * [[Strep throat]] * [[Tuberculosis]] * [[Measles]] * [[Rubella]] * [[Whooping cough]] ===Fecal-Oral Transmission=== Direct contact is rare in this route, for humans at least. More common are the indirect routes; foodstuffs or water become contaminated (by people not washing their hands before preparing food, or untreated sewage being released into a drinking water supply) and the people who eat and drink them become infected. In [[developing countries]] most sewage is discharged into the environment or on cropland as of 2006; even in [[developed countries]] there are periodic system failures resulting in a [[sanitary sewer overflow]]. This is the typical mode of transmission for the infectious agents of (at least): *[[Cholera]] *[[Hepatitis A]] *[[Polio]] *[[Rotavirus]] *[[Salmonellosis]] ===Sexual Transmission=== This refers to any disease that can be caught during sexual activity with another person, including [[sexual intercourse|vaginal]] or [[anal sex]] or (less commonly) through [[oral sex]] (see below). Transmission is either directly between surfaces in contact during intercourse (the usual route for [[bacterium|bacteria]]l infections and those infections causing sores) or from secretions ([[semen]] or the fluid secreted by the excited female) which carry infectious agents that get into the partner's blood stream through tiny tears in the [[penis]], [[vagina]] or [[rectum]] (this is a more usual route for [[virus]]es). In this second case, anal sex is considerably more hazardous since penis opens more tears in the rectum than the vagina, as the vagina is stretchier and more accommodating. Some diseases transmissible by the sexual route include (at least): *[[AIDS|HIV/AIDS]] *[[Chlamydia infection|Chlamydia]] *[[Genital warts]] *[[Gonorrhea]] *[[Hepatitis B]] *[[Syphilis]] ====Oral Sexual Transmission==== [[Sexually Transmitted Disease]]s 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 STDs 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. ===Oral Transmission=== Diseases that are transmitted primarily by oral means may be caught through direct oral contact such as [[kiss]]ing, or by indirect contact such as by sharing a drinking glass or a cigarette. Diseases that are known to be transmissible by kissing or by other direct or indirect oral contact include all of the diseases listed above as transmissible by droplet contact and also (at least): * [[Cytomegalovirus]] infections * [[Herpes simplex virus]] (especially HSV-1) * [[Infectious mononucleosis|Mononucleosis]] (Notice these are all forms of [[herpesviridae|herpes virus]].) ===Transmission by Direct Contact=== Diseases that can be transmitted by direct contact are called contagious (contagious is not the same as infectious; although all contagious diseases are infectious, not all infectious diseases are contagious). These diseases can also be transmitted by sharing a towel (where the towel is rubbed vigorously on both bodies) or items of clothing in close contact with the body (socks, for example) if they are not washed thoroughly between uses. For this reason, contagious diseases often break out in schools, where towels are shared and personal items of clothing accidentally swapped in the changing rooms. Some diseases that are transmissible by direct contact include: *[[Athlete's foot]] *[[Impetigo]] *[[Syphilis]] (on rare occasions, if an uninfected person touches a [[chancre]]) *[[Wart]]s ===Vertical Transmission=== This is from mother to child, often ''in utero'', as a result of the incidental exchange of bodily fluids (mostly blood) during [[childbirth]] or (rarely) through [[breastfeeding|breast milk]]. Some diseases that can be transmitted in this way include: *[[HIV]] *[[Hepatitis B]] *[[Syphilis]] ===Iatrogenic Transmission=== Transmission [[iatrogenic|due to medical procedures]], such as [[Injection (medicine)|injection]] or [[organ transplant|transplantation]] of infected material. Some diseases that can be transmitted iatrogenically include: *[[Creutzfeldt-Jakob Disease]] by injection of contaminated human [[growth hormone]]. *[[MRSA]] infection is often acquired as a result of a stay in hospital The route of transmission is important to [[epidemiology|epidemiologists]] because patterns of contact vary between different populations and different groups of populations depending on socio-economic, cultural and other features. For example, low personal and food hygiene due to the lack of a clean water supply may result in increased transmission of diseases by the fecal-oral route, such as [[cholera]]. Differences in incidence of such diseases between different groups can also throw light on the routes of transmission of the disease. For example, if it is noted that [[polio]] is more common in cities in underdeveloped countries, without a clean water supply, than in cities with a good plumbing system, we might advance the theory that polio is spread by the fecal-oral route. ==See also== *[[Infectious disease]] *[[Transmission risks and rates]] *[[Epidemic]] *[[Infectious disease#Transmission]] *[[Bioaerosol]] ==Sources and notes== {{Reflist}} ==Further reading== * [http://www.cdc.gov/hiv/pubs/facts/oralsexqa.htm CDC] Oral HIV Infection [[Category:Epidemiology]] [[Category:Infectious diseases]] [[Category:Diseases]] [[nl:Ziekte-overdracht]] [[pl:Droga szerzenia się zakażenia]]