Bauman Chapter 24 Answers to Critical Thinking Questions
p. 682
The United States and Russia have repeatedly agreed to destroy their stocks of the
smallpox virus, but the deadline for destruction has been postponed numerous times. In
the meantime, the entire genome of variola major has been sequenced. What reasons
can governments cite for maintaining smallpox viruses? Should all laboratory stores of
smallpox viruses be destroyed? Given that the genome of the virus has been
sequenced, and that DNA can be reconstructed if the sequence of nucleotides is known,
would elimination of all laboratory stocks really be the extinction of the smallpox virus?
No treatment for smallpox exists and the vaccine used to prevent smallpox infection is
problematic. In the face of the possibility that smallpox might be used as a weapon by
bioterrorists, governments can argue that the virus should not be destroyed until a
treatment and a better vaccine can be developed. Even with the complete genome
sequence, the basis for the virulence of smallpox is not understood. Destruction of the
laboratory stocks of smallpox will no longer mean the true extinction of the smallpox
virus, since the full genomic sequence makes it possible for those having sufficient
knowledge, skill, and resources to reconstruct the virus, although it would be no easy
task.
p. 687
After a patient complains that his eyes are extremely sensitive to light and feel gritty, his
doctor informs him that he has ocular herpes. What causes ocular herpes? Which
herpes simplex virus, type 1 or type 2, is more likely to cause ocular herpes? Why?
Herpes simplex virus introduced into the eye, e.g. by rubbing a cold sore and then the
eye, leads to ocular herpes. Herpes simplex virus type 1 is more likely to cause ocular
herpes because it is the infecting virus in about 90% of oral herpes and proximity makes
the mouth area the most likely source of transferred virus.
p. 690
Whereas many doctors are convinced that Epstein-Barr virus causes chronic fatigue
syndrome, others deny the association between EBV and the syndrome. Why is the
etiology of chronic fatigue syndrome debated when Epstein-Barr virus is present in most
cases?
Epstein-Barr virus is present in a large percentage of the population (around 70% of US
adults), so its’ presence in a person suffering from chronic fatigue syndrome is not
evidence of a causal relationship. Determining the etiology of chronic fatigue syndrome
is also hindered by the fact that many physicians do not believe that the syndrome is
real.
p. 702
1.
Most DNA viruses replicate within the nucleus of a host cell, using host enzymes to
replicate their DNA. In contrast, poxviruses replicate in the cytoplasm of host cells.
What problem does this create for poxvirus replication? How could the virus overcome
this problem?
Poxvirus replication cannot depend on the cellular machinery for DNA replication since
those enzymes are largely confined to a cell’s nucleus. The virus must therefore encode
its own DNA polymerase and other enzymes needed to replicate its DNA. Transcription
of the viral genome also requires a virus-encoded RNA polymerase.
2.
Mrs. Rathbone called the pediatrician concerning her young daughter Rene, who
had a rosy facial rash and cold-like sniffles for 2 weeks. What is the most likely cause of
Rene’s problem?
Rene most likely has erythema infectiosum (fifth disease). (“Rosy” suggests roseola, but
the symptoms are too mild and last too long for roseola.)
3.
Certain features of smallpox viruses allowed them to be eradicated in nature.
Which other DNA viruses are suitable candidates for eradication, and what features of
their biology make them suitable candidates?
None of the other DNA viruses have all the features that made it possible to wipe out
smallpox, but several of them are similar enough to be candidates. Molluscum
contagiosum is similar to smallpox virus in that it infects only humans, is non-latent and
has obvious symptoms; however, its low antigenicity could make development of an
effective vaccine difficult. Hepatitis B virus is a good candidate for eradication since it
infects only humans, is non-latent, and an effective vaccine (though expensive and
complex) is available, although the ability to cause asymptomatic infections will make it
difficult to fight unless a surveillance program is instituted. The papilloma viruses
responsible for genital warts are also candidates for eradiation: they infect humans only,
a vaccine is available for at least some, and the viruses are non-latent, but the
symptoms can sometimes be overlooked. (The herpesviruses are poor candidates
because of their ability to establish life-long infections that are often asymptomatic, but
might be accomplished if vaccination continues for several generations.)
4.
A 10-year-old girl at summer camp complains of fever, runny nose, cough, sore
throat, and tiredness. Within several hours, 36 other girls report to the infirmary with the
same signs and symptoms. Although the girls were assigned to several different cabins
and ate in two different dining halls, all of them had participated in outdoor archery, had
gone horseback riding, and had been swimming in the camp pool. Infection with what
DNA virus could account for their symptoms? The facts point to a common source of
infection; what is it? What could the camp management do to limit such an outbreak in
the future?
Epstein-Barr virus likely infects these girls, and they are suffering from infectious
mononucleosis. Since they did not share eating utensils, the pool is the probable source
of infection. Maintaining proper levels of chlorination in the pool will reduce the
likelihood of future outbreaks.
5.
A week after spending their vacation rafting down the Colorado River, all five
members of the Chen family developed cold sores on their lips. Their doctor told them
that the lesions were caused by a herpesvirus. Mr. and Mrs. Chen were stunned: Isn’t
herpes a sexually transmitted disease? How could it have affected their young children?
Herpes simplex type 1 is transmitted by contact, including kissing, and is the primary
cause of oral herpes. Mr. or Mrs. Chen or both likely had HSV-1 prior to the trip and
spread it to the children by kissing them. Intense sun exposure caused the latent virus
to reactivate and form cold sores.