:: Section 6 of 10
Because pathogenic bioaerosols can cause such extreme health effects in humans, many members of the bioaerosol field study their behavior and their effects. Pathogenic transmission can occur through several routes: person-to-person, waterborne, foodborne, vector-borne (rodent- and insect-based), airborne, or a combination of several of these. Although there are many potential forms of transmission, scientists in the air quality field of bioaerosols focus largely on pathogenic aerosols that propagate via airborne transmission. Pathogens that are transmitted primarily through the airborne route include SARS and Bird Flu, two diseases that have the potential to create epidemics.
Many pathogens can be transmitted through multiple methods. For instance, the Black Plauge of the 14th century was caused by a bacterial pathogen (Yersinia pestis), which was transmitted by both vector-borne (fleas) and airborne (sneeze or cough) transmission. Fleas containing blood from infected rats served as reservoirs for the disease. If a carrier flea then bit a person, the disease could be transmitted via the vector route. If an infected person sneezes or coughs, the bioaerosols formed can be inhaled by another person, thus propagating the disease via the airborne transmission route.
Figure 10: Example of the many paths of transmission during the Black Plague.
Enteric diseases (fecal-oral transmission) can also be acquired from bioaerosols. Common enteric pathogens include Escherichia coli and Salmonella. If a bioaerosol is inhaled, a human's natural defense mechanisms can dislodge it from the respiratory system and redirect it toward the mouth. At that point, the pathogen is preferably exhaled but potentially swallowed. If swallowed, the pathogen can then enter the enteric route and propagate the disease.
Please refer to Respiratory Deposition module for more information about the body's natural defense mechanisms against bioaerosols.