Transmission (medicine)
Encyclopedia
In medicine
and biology
, transmission is the passing of a communicable disease
from an infected host
individual or group to a conspecific
individual or group, regardless of whether the other individual was previously infected. Sometimes transmission can specifically mean infection of a previously uninfected host.
The term usually refers to the transmission of microorganism
s directly from one person to another by one or more of the following means:
Transmission can also be indirect, via another organism
, either a vector (e.g. a mosquito
) 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 pathogen
s like macroparasite
s with more complex life cycle
s.
(vectors or fomites that allow the transmission of disease without physical contact).
.
When an infected person coughs or sneezes, a percentage of their viruses will become droplet nuclei. If these droplet nuclei gain access to the eyes, nose or mouth of an uninfected person (known as a susceptible) – either directly, or indirectly after touching a contaminated surface – then the droplet nuclei may penetrate into the deep recesses of their lungs. Viral diseases that are commonly spread by coughing or sneezing droplet nuclei include (at least):
. This is the typical mode of transmission for the infectious agents of (at least):
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 bacterial 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 more elastic and more accommodating.
Some diseases transmissible by the sexual route include (at least):
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.
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):
(Notice these are all forms of herpes virus
.)
Some diseases that are transmissible by direct contact include:
(also referred to as perinatal infection
). It occurs more rarely via breast milk
.
Infectious disease
s that can be transmitted in this way include: HIV
, Hepatitis B and Syphilis
.
or transplantation
of infected material.
Some diseases that can be transmitted iatrogenically include:
that does not cause disease
itself but that transmits infection
by conveying pathogen
s from one host
to another.
The route of transmission is important to 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.
Medicine
Medicine is the science and art of healing. It encompasses a variety of health care practices evolved to maintain and restore health by the prevention and treatment of illness....
and biology
Biology
Biology is a natural science concerned with the study of life and living organisms, including their structure, function, growth, origin, evolution, distribution, and taxonomy. Biology is a vast subject containing many subdivisions, topics, and disciplines...
, transmission is the passing of a communicable disease
Infectious disease
Infectious diseases, also known as communicable diseases, contagious diseases or transmissible diseases comprise clinically evident illness resulting from the infection, presence and growth of pathogenic biological agents in an individual host organism...
from an infected host
Host (biology)
In biology, a host is an organism that harbors a parasite, or a mutual or commensal symbiont, typically providing nourishment and shelter. In botany, a host plant is one that supplies food resources and substrate for certain insects or other fauna...
individual or group to a conspecific
Conspecificity
Conspecificity is a concept in biology. Two or more individual organisms, populations, or taxa are conspecific if they belong to the same species....
individual or group, regardless of whether the other individual was previously infected. Sometimes transmission can specifically mean infection of a previously uninfected host.
The term usually refers to the transmission of microorganism
Microorganism
A microorganism or microbe is a microscopic organism that comprises either a single cell , cell clusters, or no cell at all...
s directly 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 physical contact – usually by touching soil contaminationSoil contaminationSoil contamination or soil pollution is caused by the presence of xenobiotic chemicals or other alteration in the natural soil environment....
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
Transmission can also be indirect, via another organism
Organism
In biology, an organism is any contiguous living system . In at least some form, all organisms are capable of response to stimuli, reproduction, growth and development, and maintenance of homoeostasis as a stable whole.An organism may either be unicellular or, as in the case of humans, comprise...
, either a vector (e.g. a mosquito
Mosquito
Mosquitoes are members of a family of nematocerid flies: the Culicidae . The word Mosquito is from the Spanish and Portuguese for little fly...
) or an intermediate host
Host (biology)
In biology, a host is an organism that harbors a parasite, or a mutual or commensal symbiont, typically providing nourishment and shelter. In botany, a host plant is one that supplies food resources and substrate for certain insects or other fauna...
(e.g. tapeworm in pigs can be transmitted to humans who ingest improperly cooked pork
Pork
Pork is the culinary name for meat from the domestic pig , which is eaten in many countries. It is one of the most commonly consumed meats worldwide, with evidence of pig husbandry dating back to 5000 BC....
). Indirect transmission could involve zoonoses
Zoonosis
A zoonosis or zoonoseis any infectious disease that can be transmitted from non-human animals to humans or from humans to non-human animals . In a study of 1415 pathogens known to affect humans, 61% were zoonotic...
or, more typically, larger pathogen
Pathogen
A pathogen gignomai "I give birth to") or infectious agent — colloquially, a germ — is a microbe or microorganism such as a virus, bacterium, prion, or fungus that causes disease in its animal or plant host...
s like macroparasite
Macroparasite
Macroparasites are parasites that are large enough to be seen with the naked eye, in contrast to microparasites. They grow in one host but reproduce by infective stages outside of this host. These generally include ticks, mites, nematodes, flatworms, etc., and can be either external parasites or...
s with more complex life cycle
Biological life cycle
A life cycle is a period involving all different generations of a species succeeding each other through means of reproduction, whether through asexual reproduction or sexual reproduction...
s.
Horizontal and vertical
Disease can be directly transmitted in two ways:- Horizontal disease transmissionHorizontal disease transmissionHorizontal Disease Transmission is the transmission of an infectious disease or pathogen from one individual to another in the same generation. Horizontal transmission can occur by either direct contact , or indirect contact .-External links:**...
– from one individual to another in the same generation (peers in the same age group). Horizontal transmission can occur by either direct contact (licking, touching, biting), or indirect contact air – cough or sneeze
(vectors or fomites that allow the transmission of disease without physical contact).
- Vertical disease transmission – passing a disease causing agent vertically from parent to offspring, such as perinatal transmission.
Transmission, symptoms 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 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 diarrheaDiarrhea
Diarrhea , also spelled diarrhoea, is the condition of having three or more loose or liquid bowel movements per day. It is a common cause of death in developing countries and the second most common cause of infant deaths worldwide. The loss of fluids through diarrhea can cause dehydration and...
.
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 systemRespiratory systemThe respiratory system is the anatomical system of an organism that introduces respiratory gases to the interior and performs gas exchange. In humans and other mammals, the anatomical features of the respiratory system include airways, lungs, and the respiratory muscles...
- In direct physical and indirect contact it is generally through a wound in the skin or through a mucous membraneMucous membraneThe mucous membranes are linings of mostly endodermal origin, covered in epithelium, which are involved in absorption and secretion. They line cavities that are exposed to the external environment and internal organs...
- In fecal-oral transmission, it is through the mouth.
- In vector borne transmission, it is at the bite or sting of the vector.
Droplet Contact
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 MeningitisMeningitisMeningitis is inflammation of the protective membranes covering the brain and spinal cord, known collectively as the meninges. The inflammation may be caused by infection with viruses, bacteria, or other microorganisms, and less commonly by certain drugs...
- ChickenpoxChickenpoxChickenpox or chicken pox is a highly contagious illness caused by primary infection with varicella zoster virus . It usually starts with vesicular skin rash mainly on the body and head rather than at the periphery and becomes itchy, raw pockmarks, which mostly heal without scarring...
- Common cold
- InfluenzaInfluenzaInfluenza, commonly referred to as the flu, is an infectious disease caused by RNA viruses of the family Orthomyxoviridae , that affects birds and mammals...
- MumpsMumpsMumps is a viral disease of the human species, caused by the mumps virus. Before the development of vaccination and the introduction of a vaccine, it was a common childhood disease worldwide...
- Strep throatStrep throatStreptococcal pharyngitis, streptococcal tonsillitis, or streptococcal sore throat is a type of pharyngitis caused by a group A streptococcal infection. It affects the pharynx including the tonsils and possibly the larynx. Common symptoms include fever, sore throat, and enlarged lymph nodes...
- TuberculosisTuberculosisTuberculosis, MTB, or TB is a common, and in many cases lethal, infectious disease caused by various strains of mycobacteria, usually Mycobacterium tuberculosis. Tuberculosis usually attacks the lungs but can also affect other parts of the body...
- MeaslesMeaslesMeasles, also known as rubeola or morbilli, is an infection of the respiratory system caused by a virus, specifically a paramyxovirus of the genus Morbillivirus. Morbilliviruses, like other paramyxoviruses, are enveloped, single-stranded, negative-sense RNA viruses...
- RubellaRubellaRubella, commonly known as German measles, is a disease caused by the rubella virus. The name "rubella" is derived from the Latin, meaning little red. Rubella is also known as German measles because the disease was first described by German physicians in the mid-eighteenth century. This disease is...
- Whooping cough
Viral Droplet Nuclei Transmission
Droplet nuclei are an important mode of transmission among many infectious viruses such as Influenza A. When viruses are shed by an infected person through coughing or sneezing into the air, the mucus coating on the virus starts to evaporate. Once this mucus shell evaporates the remaining viron is called a droplet nucleus or quanta. The mucus evaporation rate is determined by the temperature and humidity inside the room. The lower the humidity, the quicker the mucus shell evaporates thus allowing the droplet nuclei to stay airborne and not drop to the ground. The low indoor humidity levels in wintertime buildings ensure that higher levels of droplet nuclei will survive: droplet nuclei are so microscopic that they are able to stay airborne indefinitely on the air currents present within indoor spaces. The Wells-Riley equation predicts the infection rates of persons who shed quanta within a building and is used to calculate indoor infection outbreaks within buildings.When an infected person coughs or sneezes, a percentage of their viruses will become droplet nuclei. If these droplet nuclei gain access to the eyes, nose or mouth of an uninfected person (known as a susceptible) – either directly, or indirectly after touching a contaminated surface – then the droplet nuclei may penetrate into the deep recesses of their lungs. Viral diseases that are commonly spread by coughing or sneezing droplet nuclei include (at least):
- Common cold
- Influenza AInfluenzavirus AInfluenza A virus causes influenza in birds and some mammals and is the only species of Influenzavirus A. Influenzavirus A is a genus of the Orthomyxoviridae family of viruses. Strains of all subtypes of influenza A virus have been isolated from wild birds, although disease is uncommon...
& BInfluenzavirus BInfluenzavirus B is a genus in the virus family Orthomyxoviridae. The only species in this genus is called "Influenza B virus".Influenza B viruses are only known to infect humans and seals, giving them influenza... - MumpsMumpsMumps is a viral disease of the human species, caused by the mumps virus. Before the development of vaccination and the introduction of a vaccine, it was a common childhood disease worldwide...
- MeaslesMeaslesMeasles, also known as rubeola or morbilli, is an infection of the respiratory system caused by a virus, specifically a paramyxovirus of the genus Morbillivirus. Morbilliviruses, like other paramyxoviruses, are enveloped, single-stranded, negative-sense RNA viruses...
- RubellaRubellaRubella, commonly known as German measles, is a disease caused by the rubella virus. The name "rubella" is derived from the Latin, meaning little red. Rubella is also known as German measles because the disease was first described by German physicians in the mid-eighteenth century. This disease is...
- SARS
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 overflowSanitary sewer overflow
Sanitary sewer overflow is a condition whereby untreated sewage is discharged into the environment prior to reaching treatment facilities thereby escaping wastewater treatment. When caused by rainfall it is also known as wet weather overflow. It is primarily meaningful in developed countries,...
. This is the typical mode of transmission for the infectious agents of (at least):
- CholeraCholeraCholera is an infection of the small intestine that is caused by the bacterium Vibrio cholerae. The main symptoms are profuse watery diarrhea and vomiting. Transmission occurs primarily by drinking or eating water or food that has been contaminated by the diarrhea of an infected person or the feces...
- Hepatitis AHepatitis AHepatitis A is an acute infectious disease of the liver caused by the hepatitis A virus , an RNA virus, usually spread the fecal-oral route; transmitted person-to-person by ingestion of contaminated food or water or through direct contact with an infectious person...
- Polio
- RotavirusRotavirusRotavirus is the most common cause of severe diarrhoea among infants and young children, and is one of several viruses that cause infections often called stomach flu, despite having no relation to influenza. It is a genus of double-stranded RNA virus in the family Reoviridae. By the age of five,...
- SalmonellaSalmonellaSalmonella is a genus of rod-shaped, Gram-negative, non-spore-forming, predominantly motile enterobacteria with diameters around 0.7 to 1.5 µm, lengths from 2 to 5 µm, and flagella which grade in all directions . They are chemoorganotrophs, obtaining their energy from oxidation and reduction...
Sexual Transmission
This refers to any disease that can be caught during sexual activity with another person, including vaginalSexual intercourse
Sexual intercourse, also known as copulation or coitus, commonly refers to the act in which a male's penis enters a female's vagina for the purposes of sexual pleasure or reproduction. The entities may be of opposite sexes, or they may be hermaphroditic, as is the case with snails...
or anal sex
Anal sex
Anal sex is the sex act in which the penis is inserted into the anus of a sexual partner. The term can also include other sexual acts involving the anus, including pegging, anilingus , fingering, and object insertion.Common misconception describes anal sex as practiced almost exclusively by gay men...
or (less commonly) through oral sex
Oral sex
Oral sex is sexual activity involving the stimulation of the genitalia of a sex partner by the use of the mouth, tongue, teeth or throat. Cunnilingus refers to oral sex performed on females while fellatio refer to oral sex performed on males. Anilingus refers to oral stimulation of a person's anus...
(see below). Transmission is either directly between surfaces in contact during intercourse (the usual route for bacterial infections and those infections causing sores) or from secretions (semen
Semen
Semen is an organic fluid, also known as seminal fluid, that may contain spermatozoa. It is secreted by the gonads and other sexual organs of male or hermaphroditic animals and can fertilize female ova...
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
Penis
The penis is a biological feature of male animals including both vertebrates and invertebrates...
, vagina
Vagina
The vagina is a fibromuscular tubular tract leading from the uterus to the exterior of the body in female placental mammals and marsupials, or to the cloaca in female birds, monotremes, and some reptiles. Female insects and other invertebrates also have a vagina, which is the terminal part of the...
or rectum
Rectum
The rectum is the final straight portion of the large intestine in some mammals, and the gut in others, terminating in the anus. The human rectum is about 12 cm long...
(this is a more usual route for virus
Virus
A virus is a small infectious agent that can replicate only inside the living cells of organisms. Viruses infect all types of organisms, from animals and plants to bacteria and archaea...
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 more elastic and more accommodating.
Some diseases transmissible by the sexual route include (at least):
- HIV/AIDSAIDSAcquired immune deficiency syndrome or acquired immunodeficiency syndrome is a disease of the human immune system caused by the human immunodeficiency virus...
- Chlamydia
- Genital warts
- GonorrheaGonorrheaGonorrhea is a common sexually transmitted infection caused by the bacterium Neisseria gonorrhoeae. The usual symptoms in men are burning with urination and penile discharge. Women, on the other hand, are asymptomatic half the time or have vaginal discharge and pelvic pain...
- Hepatitis B
- SyphilisSyphilisSyphilis is a sexually transmitted infection caused by the spirochete bacterium Treponema pallidum subspecies pallidum. The primary route of transmission is through sexual contact; however, it may also be transmitted from mother to fetus during pregnancy or at birth, resulting in congenital syphilis...
- Herpes
Oral Sexual Transmission
Sexually Transmitted DiseaseSexually transmitted disease
Sexually transmitted disease , also known as a sexually transmitted infection or venereal disease , is an illness that has a significant probability of transmission between humans by means of human sexual behavior, including vaginal intercourse, oral sex, and anal sex...
s such as HIV
HIV
Human immunodeficiency virus is a lentivirus that causes acquired immunodeficiency syndrome , a condition in humans in which progressive failure of the immune system allows life-threatening opportunistic infections and cancers to thrive...
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
HIV
Human immunodeficiency virus is a lentivirus that causes acquired immunodeficiency syndrome , a condition in humans in which progressive failure of the immune system allows life-threatening opportunistic infections and cancers to thrive...
this possibility has been established. It is also responsible for the increased incidence of herpes simplex virus
Herpes simplex virus
Herpes simplex virus 1 and 2 , also known as Human herpes virus 1 and 2 , are two members of the herpes virus family, Herpesviridae, that infect humans. Both HSV-1 and HSV-2 are ubiquitous and contagious...
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 kissKiss
A kiss is the act of pressing one's lips against the lips or other body parts of another person or of an object. Cultural connotations of kissing vary widely. Depending on the culture and context, a kiss can express sentiments of love, passion, affection, respect, greeting, friendship, and good...
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):
- CytomegalovirusCytomegalovirusCytomegalovirus is a viral genus of the viral group known as Herpesviridae or herpesviruses. It is typically abbreviated as CMV: The species that infects humans is commonly known as human CMV or human herpesvirus-5 , and is the most studied of all cytomegaloviruses...
infections - Herpes simplex virusHerpes simplex virusHerpes simplex virus 1 and 2 , also known as Human herpes virus 1 and 2 , are two members of the herpes virus family, Herpesviridae, that infect humans. Both HSV-1 and HSV-2 are ubiquitous and contagious...
(especially HSV-1) - Infectious mononucleosisInfectious mononucleosisInfectious mononucleosis is an infectious, widespread viral...
(Notice these are all forms of herpes virus
Herpesviridae
The Herpesviridae are a large family of DNA viruses that cause diseases in animals, including humans. The members of this family are also known as herpesviruses. The family name is derived from the Greek word herpein , referring to the latent, recurring infections typical of this group of viruses...
.)
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 footAthlete's footAthlete's foot is a fungal infection of the skin that causes scaling, flaking, and itch of affected areas. It is caused by fungi in the genus Trichophyton and is typically transmitted in moist areas where people walk barefoot, such as showers or bathhouses...
- ImpetigoImpetigoImpetigo is a highly contagious bacterial skin infection most common among pre-school children. People who play close contact sports such as rugby, American football and wrestling are also susceptible, regardless of age. Impetigo is not as common in adults. The name derives from the Latin impetere...
- SyphilisSyphilisSyphilis is a sexually transmitted infection caused by the spirochete bacterium Treponema pallidum subspecies pallidum. The primary route of transmission is through sexual contact; however, it may also be transmitted from mother to fetus during pregnancy or at birth, resulting in congenital syphilis...
(on rare occasions, if an uninfected person touches a chancreChancreA chancre is a painless ulceration formed during the primary stage of syphilis. This infectious lesion forms approximately 21 days after the initial exposure to Treponema pallidum, the gram-negative spirochaete bacterium yielding syphilis. Chancres transmit the sexually transmissible disease of...
) - WartWartA wart is generally a small, rough growth, typically on a human’s hands or feet but often other locations, that can resemble a cauliflower or a solid blister. They are caused by a viral infection, specifically by human papillomavirus 2 and 7. There are as many as 10 varieties of warts, the most...
s
Vertical Transmission
This is from mother to child, often in utero or during childbirthChildbirth
Childbirth is the culmination of a human pregnancy or gestation period with the birth of one or more newborn infants from a woman's uterus...
(also referred to as perinatal infection
Perinatal infection
A perinatal infection is an infection caused by bacteria, viruses or, in rare cases, parasites transmitted directly from the mother to an embryo, fetus or baby during pregnancy or childbirth. The term congenital infection is also sometimes used...
). It occurs more rarely via breast milk
Breastfeeding
Breastfeeding is the feeding of an infant or young child with breast milk directly from female human breasts rather than from a baby bottle or other container. Babies have a sucking reflex that enables them to suck and swallow milk. It is recommended that mothers breastfeed for six months or...
.
Infectious disease
Infectious disease
Infectious diseases, also known as communicable diseases, contagious diseases or transmissible diseases comprise clinically evident illness resulting from the infection, presence and growth of pathogenic biological agents in an individual host organism...
s that can be transmitted in this way include: HIV
HIV
Human immunodeficiency virus is a lentivirus that causes acquired immunodeficiency syndrome , a condition in humans in which progressive failure of the immune system allows life-threatening opportunistic infections and cancers to thrive...
, Hepatitis B and Syphilis
Syphilis
Syphilis is a sexually transmitted infection caused by the spirochete bacterium Treponema pallidum subspecies pallidum. The primary route of transmission is through sexual contact; however, it may also be transmitted from mother to fetus during pregnancy or at birth, resulting in congenital syphilis...
.
Iatrogenic Transmission
Transmission due to medical procedures, such as injectionInjection (medicine)
An injection is an infusion method of putting fluid into the body, usually with a hollow needle and a syringe which is pierced through the skin to a sufficient depth for the material to be forced into the body...
or transplantation
Organ transplant
Organ transplantation is the moving of an organ from one body to another or from a donor site on the patient's own body, for the purpose of replacing the recipient's damaged or absent organ. The emerging field of regenerative medicine is allowing scientists and engineers to create organs to be...
of infected material.
Some diseases that can be transmitted iatrogenically include:
- Creutzfeldt-Jakob DiseaseCreutzfeldt-Jakob diseaseCreutzfeldt–Jakob disease or CJD is a degenerative neurological disorder that is incurable and invariably fatal. CJD is at times called a human form of mad cow disease, given that bovine spongiform encephalopathy is believed to be the cause of variant Creutzfeldt–Jakob disease in humans.CJD...
by injection of contaminated human growth hormoneGrowth hormoneGrowth hormone is a peptide hormone that stimulates growth, cell reproduction and regeneration in humans and other animals. Growth hormone is a 191-amino acid, single-chain polypeptide that is synthesized, stored, and secreted by the somatotroph cells within the lateral wings of the anterior...
. - MRSA infection is often acquired as a result of a stay in hospital
Vector borne transmission
A vector is an organismOrganism
In biology, an organism is any contiguous living system . In at least some form, all organisms are capable of response to stimuli, reproduction, growth and development, and maintenance of homoeostasis as a stable whole.An organism may either be unicellular or, as in the case of humans, comprise...
that does not cause disease
Disease
A disease is an abnormal condition affecting the body of an organism. It is often construed to be a medical condition associated with specific symptoms and signs. It may be caused by external factors, such as infectious disease, or it may be caused by internal dysfunctions, such as autoimmune...
itself but that transmits infection
Infection
An infection is the colonization of a host organism by parasite species. Infecting parasites seek to use the host's resources to reproduce, often resulting in disease...
by conveying pathogen
Pathogen
A pathogen gignomai "I give birth to") or infectious agent — colloquially, a germ — is a microbe or microorganism such as a virus, bacterium, prion, or fungus that causes disease in its animal or plant host...
s from one host
Host (biology)
In biology, a host is an organism that harbors a parasite, or a mutual or commensal symbiont, typically providing nourishment and shelter. In botany, a host plant is one that supplies food resources and substrate for certain insects or other fauna...
to another.
The route of transmission is important to epidemiologists
Epidemiology
Epidemiology is the study of health-event, health-characteristic, or health-determinant patterns in a population. It is the cornerstone method of public health research, and helps inform policy decisions and evidence-based medicine by identifying risk factors for disease and targets for preventive...
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
Cholera
Cholera is an infection of the small intestine that is caused by the bacterium Vibrio cholerae. The main symptoms are profuse watery diarrhea and vomiting. Transmission occurs primarily by drinking or eating water or food that has been contaminated by the diarrhea of an infected person or the feces...
. 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
- Transmission risks and ratesTransmission risks and ratesTransmission of an infection requires three conditions:*an infectious individual*a susceptible individual*an effective contact between themAn effective contact is defined as any kind of contact between two individuals such that, if one individual is infectious and the other susceptible, then the...
- EpidemicEpidemicIn epidemiology, an epidemic , occurs when new cases of a certain disease, in a given human population, and during a given period, substantially exceed what is expected based on recent experience...
- Infectious disease -- Transmission
- BioaerosolBioaerosolA bioaerosol is a suspension of airborne particles that contain living organisms or were released from living organisms. These particles are very small and range in size from less than one micrometer to one hundred micrometers . Bioaerosols react to air currents and move quickly or slowly...
- BugchasingBugchasingBugchasing is a slang term for the alleged practice of pursuing sexual intercourse with HIV infected individuals in order to contract HIV. Individuals engaged in this activity are referred to as bugchasers...
Further reading
- CDC Oral HIV Infection