7.2.2: Routes of Transmission
Routes of transmission can be lumped into 5 basic categories. Different pathogens may be spread using one or more of the following methods:
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Direct transmission
- Direct physical contact with an infected person including touching, kissing, or via bodily fluids (ex: bloodborne infection via blood transfusion or contact with an open wound)
- Sexual intercourse, including vaginal, oral, and anal sex, or direct contact with external genitalia
- Perinatal transmission in utero, or during a vaginal delivery
- Airborne: inhalation of large droplets from a cough or sneeze that land in the mucous membranes of a susceptible person
-
Indirect transmission
- Fomite: touching utensils, household objects, or surfaces that have been touched by an infected person or animal
- Fecal-oral: fecal contamination of fomites or hands, or contamination of food or water sources
- Food-borne or Water-borne: ingestion of contaminated food or water
- Airborne: tiny aerosols from speaking and breathing that linger in the surrounding air
- Vector: transferred via the bite of an insect such as a mosquito or tick, from an infected person or animal carrier of the pathogen to a susceptible person (Seabert et al., 2021).
Let’s use the common cold as an example of the chain of infection. Say that you have a coworker who feels a bit “under the weather”. In actuality they are the reservoir or host for one of the viruses that causes the common cold (a coronavirus, adenovirus, or rhinovirus). You happen to be walking by them when they suddenly sneeze. The portal of exit is their nose and mouth, excellently demonstrated by the high-resolution photograph below. The mode of transport might be droplets that land in your nose (direct), or if some of those tiny particles dry they could be inhaled later (indirect). Regardless, your portal of entry is the mucosa lining of your nose and respiratory tract, where the virus gets into your respiratory system and begins to multiply. Particularly if you are under a lot of stress and your immune system is suppressed, you are likely to experience symptoms of a cold in the next few days.