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. Two routes are considered to be
airborne: Airborne infections and droplet infections.
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." The size of the particles for airborne infections need to be < 5 μm. 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.
infection A common form of transmission is by way of respiratory droplets, generated by
coughing,
sneezing, or talking. Respiratory droplet transmission is the usual route for respiratory infections. Transmission can occur when respiratory droplets reach susceptible mucosal surfaces, such as in the eyes, nose or mouth. This can also happen indirectly via contact with
contaminated surfaces when hands then touch the face. Before drying, respiratory droplets are large and cannot remain suspended in the air for long, and are usually dispersed over short distances. and
coronaviruses. Spread of respiratory droplets from the wearer can be reduced through wearing of a
surgical mask. Additionally, while fecal–oral transmission is primarily considered an indirect contact route, direct contact can also result in transmission through feces. 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,
warts, and
conjunctivitis.
Sexual This refers to any infection that can be caught during sexual activity with another person, including
vaginal or
anal sex, less commonly through
oral sex (see below) and rarely through
manual 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
viruses). In this second case, anal sex is considerably more hazardous since the penis opens more tears in the rectum than the vagina, as the vagina is more elastic and more accommodating. Some infections transmissible by the sexual route include
HIV/AIDS,
chlamydia,
genital warts,
gonorrhea,
hepatitis B,
syphilis,
herpes, and
trichomoniasis.
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.
Manual sex While rare in regards to this sexual practice, some infections that can spread via manual sex include
HPV, chlamydia, and syphilis.
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.
Mother-to-child transmission This is from mother to child (more rarely father to child), often
in utero, during
childbirth (also referred to as
perinatal infection) or during postnatal physical contact between parents and offspring. In mammals, including humans, it occurs also via
breast milk (transmammary transmission).
Infectious diseases that can be transmitted in this way include: HIV, hepatitis B and syphilis. Many mutualistic organisms are transmitted vertically.
Iatrogenic Transmission
due to medical procedures, such as touching a wound, the use of contaminated medical equipment, or an
injection or
transplantation of infected material. Some diseases that can be transmitted
iatrogenically include
Creutzfeldt–Jakob disease,
HIV, and many more.
Needle sharing This is the practice of intravenous drug-users by which a needle or
syringe is shared by multiple individuals to administer
intravenous drugs such as heroin, steroids, and hormones. This can act as a vector for
blood-borne diseases, such as
Hepatitis C (HCV) and
HIV.
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. 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.
Fecal–oral In the fecal-oral route,
pathogens in
fecal particles pass from one person to the mouth of another person. Although it 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. 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. The fecal-oral route of transmission can be a public health risk for people in
developing countries who live in urban
slums without access to adequate sanitation. Here,
excreta or untreated
sewage can pollute drinking water sources (
groundwater or surface water). The people who drink the
polluted water can become infected. Another problem in some developing countries is
open defecation which leads to disease transmission via the fecal-oral route. Even in developed countries there are periodic system failures resulting in a
sanitary sewer overflow. This is the typical mode of transmission for infectious agents such as
cholera,
hepatitis A,
polio,
Rotavirus,
Salmonella, and
parasites (e.g.
Ascaris lumbricoides). ==Tracking==