New SAT Reading Practice Test 98: Influenza

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Influenza

It is a pestilence that has harried civilizations
since at least the time of Homer.
What's more, it has done so with such routine
periodicity that, in our modern age of annual
05inoculations, the enduring danger of this
disease has grown all too easy to take for
granted. Influenza owes its name to physicians
of the Italian renaissance, who believed
it was caused by inauspicious astrological
10"influences." Today, of course, we know it to
be the result of infection by one of several
closely related strains of virus. However,
unlike other viruses for which vaccines
are available—several of which, through
15tenacious public health efforts, have been
eradicated worldwide—influenza remains
a perennial menace, and due to the unique
nature of its genome, is unlikely to ever be
completely conquered.
20Traditionally, outbreaks of influenza are
classified as either "epidemic," in which the
incidence of the disease increases significantly
within a given community, or "pandemic,"
in which the incidence increases
25over a much larger region, such as a continent.
While superficially the distinction
may seem arbitrary, in fact it reflects two
well-delineated facets of the influenza virus
replication process. In the Northern hemisphere,
30"flu season" spans from November to
April, and represents an annual recurrence
of influenza epidemics among communities
situated in this part of the world. Pandemic
outbreaks, though not nearly as common,
35also seem to follow an approximate epidemiological
pattern, typically occurring about
three times per century. In the 20th century,
these outbreaks included Spanish Flu in
1918, Asian Flu in 1957, and Hong Kong Flu
40in 1968. Of the three, Spanish Flu was by
far the most devastating. With an estimated
mortality as high as 100 million, its deadliness
was on par with that of the infamous
Black Plague, which ravaged Eurasia in the
45Middle Ages.
"Antigenic drift" and "antigenic shift" are
the two chief processes through which influenza
circumvents our adaptive immunity,
and are thought to be the causes of epidemic
50and pandemic influenza, respectively. To
understand these two processes, it is necessary
to have a working knowledge of the
virus itself. There are three known species of
influenza virus—influenza A, B, and C—each
55of which consists of eight segments of RNA
contained within a protein capsid, which
in turn is surrounded by a lipid envelope.
Collectively, these RNA segments code for
eleven proteins; two of which, upon synthesis,
60are expressed on the envelope's exterior.
These two proteins are known as hemagglutinin
(HA), and neuraminidase (NA). In
terms of the viral life cycle, HA is responsible
for attaching to sugar residues that coat the
65cells of our respiratory tracts. Once the virus
has infected a cell and replicated within its
nucleus, NA cleaves these residues, allowing
the virus to spread further throughout the
body.
70Because HA and NA are the outermost
viral proteins, it is specifically against these
two "antigens" that our white blood cells
create antibodies. Furthermore, among
the diverse strains of influenza, genetically
75encoded differences exist in the types of
HA or NA expressed. This allows scientists
to sub-classify strains based on the specific
antibodies produced against them. For
instance, the H1N1 strain was responsible
80for both Spanish Flu, as well as the Swine Flu
pandemic of 2009, while H5N1 caused the
Avian Flu epidemic of 2004.
Random point mutation to the genes
encoding HA and NA is one way in which
85these subtypes evolve, and can, moreover,
interfere with the efficacy of our antibodies.
The aggregation of many point mutations
over time is referred to as antigenic drift, and
eventually results in renewed vulnerability
90to viral strains against which an individual
was previously immune. Notably, influenza
A lacks the ability to proofread and correct
its genetic material during replication, and
as a result, is prone to a much higher rate of
95mutation than other species of influenza.
For this reason in particular, influenza A is
responsible for the vast majority of annual
epidemics.
To date, 16 HA and 9 NA subtypes have
100been identified, only a fraction of which are
currently infectious to humans. However,
because the influenza genome is split into
segments, when an animal—a bird, for
instance—is co-infected with a strain specific
105to its species, as well as one capable of
infecting humans, the segments may become
intermixed during replication in a process
called "viral reassortment." When the genes
implicated in reassortment include either HA
110or NA, antigenic shift occurs, and the resulting
viral particles will express novel proteins
to which the entire human race is vulnerable.

The table shows, for each human outbreak of influenza, relevant epidemiological data, and the viral subtype involved.

Human Influenza Outbreaks

1. The structure of the passage is best described as a

  • A. broad survey followed by a technical analysis.
  • B. historical overview followed by a logical argument.
  • C. general critique followed by experimental summaries.
  • D. persuasive presentation followed by a research summary.

2. Lines 12-19 ("However . . . conquered") most strongly suggest that influenza

  • A. will continue to be a threat despite scientific advances.
  • B. can be fully eradicated with sufficient research funding.
  • C. is unique among diseases in the severity of its symptoms.
  • D. has been eliminated as a pervasive threat to humanity.

3. As used in line 21, the word "epidemic" would best describe which of the flu outbreaks in the table?

  • A. 1889
  • B. 1957
  • C. 2009
  • D. 2013

4. Based on the passage, would antigenic drift or antigenic shift result in greater fundamental changes to genetic structure?

  • A. Antigenic drift because it results in increasing vulnerability to viruses
  • B. Antigenic drift because it can easily spread throughout the body
  • C. Antigenic shift because it entails genetic replication
  • D. Antigenic shift because it involves interspecies genome exchange

5. Which option gives the best evidence for the answer to the previous question?

  • A. Lines 61-65 ("These . . . tracts")
  • B. Lines 65-69 ("Once . . . body")
  • C. Lines 83-91 ("Random . . . immune")
  • D. Lines 101-108 ("However . . . reassortment")

6. The primary purpose of the paragraph in lines 83-98 is to

  • A. explain how HA and NA antibodies lead to genetic mutations resulting in flu.
  • B. contrast the process of antigenic drift with that of antigenic shift.
  • C. describe the mechanism whereby a particular flu type becomes quite harmful.
  • D. critically respond to widespread misconceptions about flu vaccines.

7. As used in line 92, the word "ability" most closely means

  • A. aptitude.
  • B. capacity.
  • C. skill.
  • D. talent.

8. Given the data in the table, which of these flu outbreaks most likely resulted in the greatest number of deaths?

  • A. Russian
  • B. Asian
  • C. Hong Kong
  • D. Avian

9. Based on the table and the passage, which flu outbreaks (given by year of occurrence) would most likely result in the human body producing similar chemicals to fight them?

  • A. 1889 and 1957
  • B. 1918 and 2009
  • C. 1968 and 2013
  • D. 2005 and 2013

10. Which option gives the best evidence for the answer to the previous question?

  • A. Lines 37-45 ("In the . . . Ages")
  • B. Lines 53-57 ("There are . . . envelope")
  • C. Lines 78-82 ("For instance . . . 2004")
  • D. Lines 108-112 ("When . . . vulnerable")

11. According to the information in the table, which of these options gives the most logical possible reason that the flus of 2005 and 2013 resulted in relatively few cases?

  • A. These strains of flu are transmitted via blood rather than through the more contagious respiratory method.
  • B. Asia, and particularly China, have lower population density than the global norm.
  • C. Those humans infected were more likely to die before they could transmit the disease.
  • D. The reservoir of the human influenza outbreak had birds as its source.