Micro pretest virol10. Which one of the following statements best describes interferon's suspected mode of action in producing resistance to viral infection? a. It stimulates a cell-mediated immunity b. It stimulates humoral immunity c. Its direct antiogy

The clinical picture of arbovirus infection fits one of three categories: encephalitis, hemorrhagic fever, or fever with myalgia. One of the charac- teristics of arboviruses is that they a. Are transmitted by arthropod vectors b. Are usually resistant to ether c. Usually cause symptomatic infection in humans d. Are closely related to parvoviruses

a. Are transmitted by arthropod vectors. Arboviruses (arthropod- borne viruses) may or may not be surrounded by a lipid envelope, although most are inactivated by lipid solvents such as ether and may contain either double-stranded or single-stranded RNA. Physicochemical studies have demonstrated a great heterogeneity among these viruses. Arboviruses cause disease in vertebrates; in humans, encephalitis is a frequent arbovirus illness. Most human infections with arbovirus, however, are asymptomatic.

Coronaviruses are recognized by club-shaped surface projections that are 20 nm long and resemble solar coronas. These viruses are characterized by their ability to a. Infect infants more frequently than adults b. Cause the common cold c. Grow well in the usual cultured cell lines d. Grow profusely at 50°C e. Agglutinate human red blood cells

b. Cause the common cold. Coronaviruses, discovered in 1965, are thought to be a major agent of the common cold, especially in older children and adults. The virion is known to contain RNA, but other ele- ments of its structure are unclear. At 34°C, viral multiplication is profuse; however, infectivity is greatly reduced at higher temperatures or following extended incubation.

A tube of monkey kidney cells is inoculated with nasopharyngeal secretions. During the next 7 days, no cytopathic effects (CPEs) are observed. On the eighth day, the tissue culture is infected accidentally with a picornavirus; nevertheless, the culture does not develop CPEs. The most likely explanation of this phenomenon is that a. The nasopharyngeal secretions contained hemagglutinins b. The nasopharyngeal secretions contained rubella virus c. Picornavirus does not produce CPEs d. Picornavirus does not replicate in monkey kidney cells e. Monkey kidney cells are resistant to CPEs

b. The nasopharyngeal secretions contained rubella virus. Rubella virus does not pro- duce cytopathic effects (CPEs) in tissue-culture cells. Moreover, rubella- infected cells challenged with a picornavirus are resistant to subsequent infection and thus would not exhibit CPEs. Monkey kidney cells infected only with picornavirus would show CPEs.

An HIV-positive patient asks you if you can tell him the chances of him progressing to symptomatic AIDS. Which one of the following tests would be most useful? a. CD4 lymphocyte count b. HIV antibody test c. HIV RT PCR d. Neopterin e. HIV p24 antigen

c. HIV RT PCR. HIV RT PCR, a nucleic acid amplification test for HIV RNA, has recently been shown to be the most valuable test for a) monitoring a patient's progress during triple drug ther- apy and b) determining the chances of progression to AIDS. A viral load of 750,000 copies per ml significantly increases the chance of progression to AIDS within 5 years.

Infection with herpes simplex virus, a common human pathogen, is best described by which of the following statements? a. The CNS and visceral organs are usually involved b. It rarely recurs in a host who has a high antibody titer c. It can be reactivated by emotional disturbances or prolonged exposure to sun- light d. Initial infection usually occurs by intestinal absorption of the virus e. Infection with type 1 virus is most common

c. It can be reactivated by emotional disturbances or prolonged exposure to sun-light. The initial infection by herpes simplex virus is often inapparent and occurs through a break in the skin or mucous membranes, such as in the eye, throat, or genitals. Latent infection often persists at the initial site despite high antibody titers. Recurrent disease can be triggered by temperature change, emotional distress, and hormonal factors. Type 1 herpes simplex virus is usually, but not exclusively, associated with ocular and oral lesions; type 2 is usually, but not exclusively, associated with genital and anal lesions. Type 2 infection is more common. In addition to mucocutaneous infections, the CNS and occasionally visceral organs can be involved.

Which of the following viruses causes an acute febrile rash and pro- duces disease in immunocompetent children but has been associated with transient aplastic crises in persons with sickle cell disease? a. Rubeola b. Varicella-zoster c. Parvovirus d. Rubella e. Herpes simplex

c. Parvovirus. Parvovirus B 19 is the causative agent of erythema infectiosum (fifth disease). It is associated with transient aplastic crisis in persons with hereditary hemolytic anemia. In adults, it is also associated with polyarthralgia.

Infectious mononucleosis, a viral disorder that can be debilitating, is characterized by which of the following statements? a. It is most prevalent in children less than 14 years old b. It is caused by a rhabdovirus c. The causative pathogen is an Epstein-Barr virus d. Affected persons respond to treatment with the production of heterophil anti- bodies e. Ribavirin is the treatment of choice

c. The causative pathogen is an Epstein-Barr virus. All of Koch's postulates have been verified for the relationship between infectious mononucleosis and Epstein-Barr virus, a herpesvirus. However, the relationship between this virus and Burkitt's lymphoma, sarcoid, and systemic lupus erythematosus (SLE) is less clear. Infectious mononucleosis is most common in young adults (14 to 18 years of age) and is very rare in young children. There is no specific treatment. Heterophil antibody titer is helpful in diagnosis, but is not expressed as a function of clinical recovery.

Which one of the following statements best describes interferon's suspected mode of action in producing resistance to viral infection? a. It stimulates a cell-mediated immunity b. It stimulates humoral immunity c. Its direct antiviral action is related to the suppression of messenger RNA for- mation d. Its action is related to the synthesis of a protein that inhibits translation or tran- scription e. It alters the permeability of the cell membrane so that viruses cannot enter the cell

d. Its action is related to the synthesis of a protein that inhibits translation or transcription. Interferon is a protein produced by cells in response to a viral infection or certain other agents. Entering uninfected cells, interferon causes production of a second protein that alters protein synthesis. As a result of inhibition of either translation or transcription, new viruses are not assembled following infection of interferon protected cells.

This HIV-positive patient with a viral load of 750,000 copies of HIV RNA/ml and a total CD4 count of 50 is at an increased risk for a number of infectious diseases. For which of the following diseases is the patient at no more added risk than an immunocompetent host? a. Pneumocystic pneumonia b. Mycobacterial disease c. Kaposi's sarcoma d. Pneumococcal pneumonia e. Herpes simplex virus

d. Pneumococcal pneumonia. Kaposi's sarcoma, which has been linked to herpesvirus type 8, pneumocystis, and mycobacterial disease are three of the most prevalent opportunistic infections. While HIV-positive patients contract pneumococcal pneumonia, they are probably at no more risk than the general population, as protection against pneumococcal disease is linked to the presence of anticapsular antibody.

The latest and most effective therapy for AIDS patients includes azi- dothymidine (AZT), dideoxyinosine (DDI), and saquinavir or similar agents. Use of these three drugs would inhibit which of the following viral processes? a. RNase, DNase b. gp120 formation c. p24 antibody expression d. All membrane synthesis e. Reverse transcriptase, protease

e. Reverse transcriptase, protease. The advent of triple therapy or a therapeutic "cocktail" has had a marked effect on AIDS patients. The combination of drugs work together as reverse tran- scriptive inhibitors and a protease inhibitor. Patients improve rapidly, their CD4 lymphocyte counts increase, and their HIV viral load is drastically reduced, often to <50 copies per ml.

An HIV-positive patient prior to being treated with AZT, DDI, and saquinavir has a CD4 lymphocyte count and an HIV RNA viral load test done. Results are as follows: CD4: 50 CD4 lymphocytes per microliter HIV RNA: 750,000 copies per ml Which of the following statements best describes the above patient? a. This patient is no longer in danger of opportunistic infection b. The 5-year prognosis is excellent c. The patient's HIV screening test is most likely negative d. The patient is not infectious e. The viral load of 750,000 copies per ml suggests that the patient will respond to triple therapy

e. The viral load of 750,000 copies per ml suggests that the patient will respond to triple therapy. On the other hand, an untreated HIV- positive patient with a low CD4 and a high viral load a) is at increased risk of opportunistic infection and b) has a much greater chance of developing AIDS than if the viral load was <50,000. The patient is infectious and his HIV antibody screening test will be positive. The high viral load, however, is not a predictor of response to therapy. Many patients with high viral loads do very well on triple therapy, although resistance to one or more of the agents may subsequently occur. A low CD4 count does not predict pro- gression to AIDS but does indicate increased chance of opportunistic infec- tion such as those listed.