Although genetic mutations in bacteria and viruses can lead to epidemics, some epidemics are caused by bacteria and viruses that...
GMAT Reading Comprehension : (RC) Questions
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 or 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 nineteenth 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 albopictus.
The passage suggests that a lack of modern sanitation would make which of the following most likely to occur?
Progressive Passage Analysis
| Text from Passage | Analysis |
|---|---|
| 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. |
What it says: There are two types of epidemic causes: (1) germs that mutate, and (2) germs that DON'T mutate but still cause epidemics. What it does: Sets up the main contrast and tells us the passage will focus on type #2 (the "although" structure signals this). Connection to Previous Sentences: This is our starting point - no previous context to connect to yet. |
| In analyzing the latter, scientists have discovered the importance of social and ecological factors to epidemics. |
What it says: When scientists study the non-mutating germ epidemics, they found that social and environmental factors matter a lot. What it does: Provides the key insight/answer for how unchanged germs cause epidemics. Reading Strategy Insight: This is the central thesis! Everything else will be examples of this principle. |
| 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 or adulthood, at which time polio infection produced paralysis. |
What it says: Polio became epidemic in 1900s America because better sanitation meant people got infected later in life (as teens/adults), when polio causes paralysis. What it does: Provides first concrete example of the social/ecological factor principle. |
Author's Purpose
The author aims to explain how epidemics can emerge without genetic mutations in the pathogens themselves. By examining polio and Lyme disease as case studies, the author demonstrates how social and ecological changes can transform previously manageable diseases into serious epidemics.
3. Question Analysis:
The question asks what would "most likely" occur if there was a "lack of modern sanitation." This is asking us to reverse-engineer the relationship between sanitation and disease outcomes that the passage establishes.
Connecting to Our Passage Analysis:
Our passage analysis reveals crucial information about the relationship between sanitation and epidemics:
- The passage establishes that modern sanitation helped prevent typhoid epidemics - this is stated directly in sentence 5: "the hygiene that helped prevent typhoid epidemics"
- The polio example shows how modern sanitation created unintended consequences by delaying exposure, but this was specifically about timing of infection, not whether epidemics occurred
- The passage demonstrates that social and ecological factors (including sanitation) determine epidemic patterns with unchanged germs
- The key insight from our analysis is that sanitation changes can either prevent or cause epidemics depending on the specific disease mechanism
Prethinking:
If we remove modern sanitation, we should expect:
- Direct reversal of what modern sanitation accomplished
- The passage explicitly states modern sanitation "helped prevent typhoid epidemics"
- Therefore, lack of modern sanitation would most likely lead to typhoid epidemics
- The polio case is more complex because lack of sanitation would actually prevent the paralytic epidemic (by allowing early infection), but typhoid has a direct, straightforward relationship with sanitation
Why It's Wrong:
• Lyme disease is caused by deer ticks and bacteria, not sanitation issues
• The passage shows Lyme epidemics result from increased deer populations and suburban expansion
• Sanitation has no connection to tick-borne diseases in the passage
Common Student Mistakes:
1. Thinking all diseases mentioned are related to sanitation?
→ Focus on which diseases the passage specifically connects to sanitation
2. Confusing ecological factors with sanitation factors?
→ Distinguish between different types of social/ecological changes
Why It's Wrong:
• Dengue fever is transmitted by mosquitoes, not through sanitation-related pathways
• The passage shows dengue epidemics result from mosquito proliferation due to ecological changes
• No connection is made between dengue and sanitation levels
Common Student Mistakes:
1. Assuming all epidemic diseases are sanitation-related?
→ Pay attention to the specific transmission mechanism for each disease
2. Confusing vector-borne diseases with sanitation-related diseases?
→ Vector-borne diseases depend on animal carriers, not cleanliness
Why It's Right:
• The passage explicitly states that modern sanitation "helped prevent typhoid epidemics"
• This creates a direct, logical connection: if modern sanitation prevents typhoid epidemics, then lack of modern sanitation would allow typhoid epidemics
• Typhoid is the only disease in the passage with a clear, straightforward relationship to sanitation levels
Key Evidence: "Thus, the hygiene that helped prevent typhoid epidemics indirectly fostered a paralytic polio epidemic."
Why It's Wrong:
• The passage shows that lack of modern sanitation would actually prevent paralytic polio in infants
• Poor sanitation leads to early infection during infancy, which "typically provided lifelong immunity without paralysis"
• This choice reverses the actual relationship described in the passage
Common Student Mistakes:
1. Thinking poor sanitation always leads to more severe disease?
→ The polio example shows poor sanitation can actually prevent the severe form
2. Missing the age-specific effects described in the passage?
→ Pay attention to when infection occurs and its different outcomes
Why It's Wrong:
• This contradicts the passage's explanation of how sanitation affects polio
• Lack of modern sanitation would lead to early childhood infection, preventing the paralytic form that occurs in adolescents and adults
• Modern sanitation creates this problem by delaying exposure; removing it would eliminate this specific epidemic pattern
Common Student Mistakes:
1. Thinking worse sanitation always means worse epidemics?
→ The passage shows sanitation changes can have complex, sometimes counterintuitive effects
2. Not tracking the cause-and-effect chain for polio?
→ Follow the logic: modern sanitation → delayed infection → paralysis in older individuals