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Unit 19: Biology Part 2
the protozoan shown in the picture
above which causes diarrhea, is
spread in water.
Some pathogens, including the
fungus that causes athlete’s foot,
or the bacterium that causes the
skin disease impetigo, are spread
when they get onto objects or
surfaces.
If someone with athlete’s foot
walks on the floor of a public
shower, and then you walk on that
same floor, the disease can be
spread to you. Similarly sharing a
towel or piece of clothing with
someone who has impetigo can
spread this disease to you.
A common way for pathogens to be
spread is in the air. This is the
method for spreading many
pathogens that causes diseases of
the throat and lungs. When a
person sneezes or coughs, tiny
droplets are released into the air.
Each of these drops contains
pathogens, such as the pathogens
for the cold and flu. If you breathe
in these pathogens, you can get
the disease.
Another method for spreading
pathogens is through the use of a
vector. Vectors are organisms
that carry the disease from one
person (or other animal) to
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another. Vectors are usually
insects, and include ticks and
mosquitoes. When the insect bites
a person with the disease, it picks
up the pathogen. Usually, the
pathogen does not make the vector
sick. However, when the vector
bites another person, they transfer
the disease to them.
Figure 70 – A mosquito can act
as a vector when it bites a
person with a disease.
As you read above, malaria is one
disease transferred by a vector.
Ticks act as a vector for Lyme
disease. Mosquitoes can also be
vectors for West Nile Virus, a
disease that has spread rapidly in
the United States over the last
dozen years.
Avoid the Spread of
Infectious Diseases
The single most effective way of
not getting an infectious disease is
to wash your hands often. This
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