Infectious Disease Transmission: 3 Main Pathways
Pathogens spread through three fundamental pathways:
- Direct contact: Physical touch with infected person/animal — skin, mucosa, sexual, vertical. Examples: HSV, HPV, staph, scabies, Ebola.
- Indirect contact (fomite): Touching contaminated objects/surfaces — doorknobs, towels, medical equipment, toys. Examples: norovirus, C. diff, rhinovirus, SARS-CoV-2.
- Airborne: Inhalation of infectious aerosols/droplets from cough/sneeze/talk/breath. Subtypes:
- Droplet (>5 µm, short-range): influenza, pertussis
- Airborne (≤5 µm, long-range): TB, measles, varicella
Additional Routes
- Vector-borne: Mosquito (malaria, dengue), tick (Lyme), flea (plague).
- Vehicle-borne: Food (Salmonella), water (cholera), blood (HIV, HCV), IV drugs.
- Vertical: Mother→fetus/infant (HIV, syphilis, CMV, Zika).
Most pathogens use multiple routes. Control measures target the dominant transmission mode.
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