isms can transmit disease through air. They can travel one meter or more through
an air medium to spread infection.
Airborne pathogens have the greatest chance of infecting new individuals when
these individuals are crowded together indoors or in a climate-controlled build-
ing where heating and air conditioning units regulate temperature and very
little fresh air enters the building. Airborne pathogens can fall to the floor and
combine with dust particles. This dust can then be stirred up with walking, dry
mopping, or changing bedding and clothing. Examples of diseases that are trans-
mitted by airborne transmissions and dust particles are measles, chickenpox, histo-
plasmosis, and tuberculosis.
Waterborne microorganisms that cause pathologies do not grow in pure water.
They can survive in water with small amounts of nutrients but thrive in polluted
water, such as water contaminated with fertilizer and sewage (which is rich in
nutrients). Waterborne pathogens are usually transmitted in contaminated water
supplies by either untreated or inadequately treated sewage. Indirect fecal-oral
transmission of pathogens occurs when the disease-causing microorganism liv-
ing in the fecal matter of one organism infects another organism. Bacterial
pathogens infect the digestive system, causing gastrointestinal signs and symp-
toms. Examples of waterborne diseases are shigellosis and cholera.
Foodborne pathogens are normally transmitted through improperly cooked
or improperly refrigerated food, or unsanitary conditions. Improper hygiene of
the part of food handlers also plays a key role in foodborne transmission. Food-
borne pathogens can produce gastrointestinal signs and symptoms. Examples of
foodborne diseases are salmonellosis, typhoid fever, tapeworm, and listeriosos.Vector Transmission
Vector spread is the transmission of an infectious agent by a living organism
to humans. Most vectors are ticks, flies, and mosquitoes. These organisms are
called arthropods. Vectors can transmit disease in two ways. First, mechanical
vectors can passively transmit disease with their bodies. An example is the
common housefly.
These animals commonly feed on fecal matter. They then fly to feed on human
food, transmitting pathogens along the way. Keeping mechanical vectors away
from food preparation and eating areas are means of prevention. Remember: The
fly that is walking across your picnic lunch may have just walked across dog or
cat feces. Examples of a few diseases transmitted by mechanical vectors are
diarrhea caused by E. colibacteria, conjunctivitis, and salmonellosis.
The second type of vectors are biological vectors and can actively transmit
disease-causing pathogens that complete part of their life cycle within the vector.
In most vector-transmitted diseases, a biological vector is the host for a phase of(^202) CHAPTER 13 Epidemiology and Disease