PT120.S2.P4.Q25

PrepTest 120 - Section 2 - Passage 4 - Question 25

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P1

Until recently, biologists were unable to explain the fact that pathogens—disease-causing parasites—have evolved to incapacitate, and often overwhelm, their hosts. ████ ████████ ██ ██ ████ ████ ███ ██████████ ████ ██ █████████████ █████████████████ ██ ████████ ████ ███ ████████ ██████████ ███████ █ ██████ ████████████ ████ ████ ██ █████ ██ ███ ████ ████ █████████ ████ ██ ███ ████ █████ █████ ████ ███ ████ ██████ ███ █████████ █████████ ████ ██████ ███████ █████ █████ ███████ ███

Puzzling Phenomenon · Pathogens incapacitate and kill hosts
This is puzzling because the prevailing view is that parasites need their hosts for long-term survival.
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Hypothesis · Trade-off
Pathogen can cause hosts to be very sick or even die if it can spread to a new host. So it's trading away staying in the current host for jumping to a new host.
P2

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Implication · Virulence is function of mode transmission
Virulence means the ability to defeat the host's defenses and incapacitate the host.
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Example · Close contact transmission requires low virulence
Rhinoviruses (common cold) requires physical contact for transmission. Hence, it cannot be too virulent. If it were, then the host would be confined in solitude (or die) and the virus would not be able to jump to a new host. It needs to be only mildly virulent so that the host can help it jump to new hosts.
P3

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Example · Vector transmission requires high virulence
If a pathogen can be transmitted via a vector (e.g., mosquito), then virulence can and perhaps must be high. It needs to reproduce so extensively (and hence severely harm the host) such that the vector (e.g., mosquito) can acquire enough of the pathogen to transmit it to a new host.
P4

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Anomalies · "Sit and wait" pathogens
In general, the literature supports the hypothesis. But "sit and wait" pathogens like diphtheria and tuberculosis are directly transmitted yet lethal. They can do this because they can survive outside their hosts for up to months. This makes them the most dangerous kind of pathogen.
Passage Style
Phenomenon-hypothesis (RC)
Single position
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25.

The passage implies that which ███ ██ ███ █████████ ██ █ ██████ ████ ████████████ ███ ████████ ██ ██ ██████████ █████████

a

They immobilize their █████ ██████ ████ ████ █ ██████ ██ █████████ ███████████ ██████ ██ ████ ████████ ██ ███ ██████

Anti-supported. The rhinovirus needs proximity to be transmitted; this indicates the rhinovirus is unlikely to immobilize their hosts. If hosts were immobilized, they would be less likely to move near people and transmit the virus to new hosts.

22%
b

They cannot survive ███████ █████ █████ ████ ██████ ██ ██ ███████████ ████ █████████████ █████ ██ ███ ██████

This is supported by the end of P4. Some pathogens that transmit directly are known as “sit and wait” because they can survive outside a host long enough to transmit to a new host. These pathogens, which can survive outside a host for weeks or months, are contrasted with rhinoviruses, which die in a few hours. If what defines “sit and wait” pathogens is their ability to survive outside a host long enough to transmit to a new host, this implies rhinoviruses do not have this ability.

62%
c

They cannot reproduce ██ ███████ ██████████ ██ █████ ███████ ██ ██████ ████ ██████ █████ ██ ████ ██ ███ ██████

Rhinoviruses aren’t vector-based. So the reason rhinoviruses aren’t very virulent would not relate to vectors.

4%
d

They cannot survive ████ ██████ ██ ██ █████████████ ████ ██ ██ ██████ ██ ██ ████████

Rhinoviruses aren’t vector-based. So the reason rhinoviruses aren’t very virulent would not relate to vectors.

10%
e

They produce thousands ██ ███ ████████████ ████ ████

We have no reason to think the production of new rhinoviruses would make rhinoviruses less virulent. If anything, producing thousands of new viruses might be a reason to think rhinoviruses should be more virulent.

2%

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