Transmission is the transfer of a disease from an infected individual to an uninfected person. Disease causing microorganisms can be transmitted from one person to another by one or more of the following means:
- coughing or sneezing on another person
- direct physical contact - touching an infected person, including sexual contact
- indirect contact - usually by touching a contaminated surface
- airborne transmission - if the microorganism is contracted through the air
- fecal-oral transmission - from contaminated food or water sources
- vector borne transmission - carried by insects and other animals
Microorganisms are usually transmitted from an individual to another in the form of bacteria or virus. They vary in there ability to survive outside the body of the carrier, such as the human body.
HIV can be transmitted in the sexual fluids, blood or breast milk of an infected person. HIV prevention therefore involves a wide range of activities including prevention of mother-to-child transmission, harm reduction for using contaminated needles and precautions for health care personnel.
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
Droplet Contact
Microorganisms (bacteria and viruses) that cause disease may be transmitted from one person to another by aerosols 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
- 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