Although genetic mutations in bacteria and viruses can lead
to epidemics, some epidemics are caused by bacteria and viruses that have
undergone no significant genetic change. In analyzing the latter, scientists have
discovered the importance of social and ecological factors to epidemics.
Poliomyelitis, for example, emerged as an epidemic in the United States in the
twentieth century; by then, modern sanitation was able to delay exposure to
polio until adolescence of adulthood, at which time polio infection produced
paralysis.
Previously, infection had occurred during infancy, when it typically
provided lifelong immunity without paralysis. Thus, the hygiene that helped
prevent typhoid epidemics indirectly fostered a paralytic polio epidemic.
Another example is Lyme disease, which is caused by bacteria that are
transmitted by deer ticks. It occurred only sporadically during the late
nineteen century but has recently become prevalent in parts of the United
States, largely due to an increase in the deer population that occurred
simultaneously with the growth of the suburbs and increased outdoor
recreational activities in the deer’s habitat. Similarly an outbreak of dengue
hemorrhagic fever became an epidemic in Asia in the 1950’s because of
ecological changes that caused Aedes aegypti, the mosquito that transmits the
dengue virus, to proliferate. The stage is now set in the United States for a
dengue epidemic because of the inadvertent introduction and wide dissemination
of another mosquito, Aedes albopicuts.
1.
The passage suggests that a lack of modern
sanitation would make which of the following most likely to occur?
A.
An
outbreak of Lyme disease
B.
An outbreak of dengue hemorrhagic fever
C.
An epidemic of typhoid
D.
An epidemic of paralytic polio among infants
2.
According to the passage, the outbreak of dengue
hemorrhagic fever in the 1950’s occurred for which of the following reasons?
A.
The mosquito Aedes aegypti was newly introduced
into Asia.
B.
The mosquito Aedes aegypti became more numerous.
C.
The mosquito Aedes albopictus became infected
with the dengue virus.
D.
Individuals who would normally acquire immunity
to the dengue virus as infants were not infected until later in life.
3.
It can be inferred from the passage that Lyme
disease has become prevalent in parts of the United States because of which of
the following?
A.
The inadvertent introduction of Lyme disease
bacteria to the United States
B.
The inability of modern sanitation methods to
eradicate Lyme disease bacteria
C.
A genetic mutation in Lyme disease bacteria that
makes them more virulent
D.
An increase in the number of humans who
encounter deer ticks
4.
Which of the following can most reasonably be
concluded about the mosquito Aedes albopictus on the basis of information given
in the passage?
A.
It is native to the United States.
B.
It can proliferate only in Asia.
C.
It transmits the dengue virus
D.
It caused an epidemic of dengue hemorrhagic
fever in the 1950’s
5.
Which of the following best describes the
organization of the passage?
A.
A paradox is states, discussed, and left
unresolved.
B.
Two opposing explanations are presented, argued,
and reconciled.
C.
A theory is proposed and is then following by
descriptions of three experiments that support the theory.
D.
A generalization is stated and is then followed
by three instances that support the generalization.
6.
Which of the following, if true, would most
strengthen the author’s assertion about the cause of the Lyme disease outbreak
in the United States?
A.
The deer population was smaller in the late
nineteenth century than in the mid twentieth century.
B.
Interest in outdoor recreation began to grow in
the late nineteenth century.
C.
In recent years the suburbs have stopped growing.
D.
Outdoor recreation enthusiasts routinely take
measures to protect themselves against Lyme disease.
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