Reading Comprehension Home Exercise – 01

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

Answers and Explanations:

 

1.       C      since the question asks for an inference about a lack of modern sanitation, begin by examining what the passage says about the presence of modern sanitation. We are given the role of modern sanitation in delaying the onset of polio. The passage also states that the hygiene that helped prevent typhoid epidemics indirectly fostered a paralytic polio epidemic. It is reasonable to infer from this statement that a lack of modern sanitation could lead to a typhoid epidemic.

2.       B     the question asks for information explicitly stated in the passage, although in slightly different language. Where the 1950’s outbreak of dengue fever is discussed. The outbreak became an epidemic in Asia because of ecological changes that caused Aedes aegypti, the mosquito that transmits the dengue virus, to proliferate. 

3.       D      The Lyme disease is caused by bacteria carried by deer ticks. It has become prevalent in parts of the United States as the deer population has grown. This population growth has occurred at the same time that the suburbs have expanded and outdoor activities in the deer’s habitat have increased. Thus, it is logical to infer that more people are encountering the deer ticks that carry the disease.