PT120.S2.P4.Q25 > Analytics

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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.

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.

Implication · Virulence is function of mode transmission

Virulence means the ability to defeat the host's defenses and incapacitate the host.

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.

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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.

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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

25.

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

Question Type

Stated

The author discusses rhinoviruses in P2 and at the end of P4. At the end of P4, the author contrasts “sit and wait” viruses with rhinoviruses. “Sit and wait” viruses are among the most dangerous pathogens, because they can survive outside a host long enough to be transmitted to a new host. This suggests that rhinoviruses, which aren’t “sit and wait” viruses, and only survive for up to a few hours, are not as dangerous because they can’t survive long enough outside a host to be transmitted to a new host.

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%

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%

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

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

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

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

10%

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.

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PrepTest 120 - Section 2 - Passage 4 - Question 25

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PrepTest 120 - Section 2 - Passage 4 - Question 25

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