Bauman Chapter 1 Answers to Critical Thinking Questions s1

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.