DMF Week 8 SAQ

1

Which one of the following statements is correct?


  Infection with one serotype of Hepatitis C virus (HCV) protects against infection with other serotypes of HCV.

  A vaccine which uses HCV grown in cell cultures has been very successful

  HCV nucleic acid replication is carried out by a reverse transcriptase, which can be targeted by antiviral agents

  Infection with HCV is best treated with a combination of ribavirin and alpha-interferon

  Infection with HCV is a milder illness than infection with HBV, and rarely results in chronic infection with the virus.


1 is incorrect: The RNA genome of HCV is susceptible to a high rate of mutations that result in significant immune evasion. 2 is incorrect: HCV cannot be cultured, and there is no vaccine available. 3 is incorrect: Reverse transcription is a characteristic of HIV and HBV. 4 is correct. 5 is incorrect: Infection with HCV results in a significantly higher rate of chronic infection than does infection with HBV.

2

Which one or more of the following statements about HIV transmission is correct?

A - Macrophages and helper T cells can be infected by HIV because both cell types express CD4.

B - In vitro infection of macrophages and T cell lines by different sub-types of HIV is determined by the expression of specific chemokine receptors on these cells.

C - Newly released HIV virions require the action of a virus encoded protease to become fully infectious

D - HIV is a DNA virus which integrates into the host cell genome and thus evades the immune system.


  A, B, and C only are correct

  A and C only are correct

  B and D only are correct

  D only is correct

  All are correct


Macrophages and T cells both express CD4. However, they express different chemokine receptors, which allow different sub-types (macrophage tropic, T cell tropic) of virus to infect these different cells. Newly released virions require cleavage of the polyproteins in the immature virion by viral proteases for full infectivity. D is incorrect: HIV is an RNA virus.

3

Which one or more of the following statements about pandemic influenza is correct?

A - The existing influenza vaccine can provide protection against pandemic influenza

B - Aquatic water birds have undergone mass slaughter in Asia in an attempt to curb the spread of avian influenza to humans

C - A new pandemic of influenza virus is predicted to spread around the globe in about 12 months, which will be sufficient time for a vaccine to be made against the newly emerging strain

D - Antivirals such as the neuraminidase blockers may be effective against a newly emerging strain of virus but the supply might be insufficient.


  A, B, and C only are correct

  A and C only are correct

  B and D only are correct

  D only is correct

  All are correct


1 is incorrect: Pandemic influenza, by definition, is caused by a new strain of influenza against which no protection exists. Since it is a new strain, it is unlikely that a current vaccine will protect against it. And even when we know a new strain exists, it will take much longer than one year to produce enough vaccine to vaccinate enough people to block the transmission of infection. Whilst aquatic water birds provide the reservoir of infection, removing this reservoir by culling is impossible. D is correct: As well, it should be noted that some isolates of avian influenza have been shown to have reduced susceptibility to some of these agents.

4

Which one or more of the following statements about cervical carcinoma is correct?

A - HPV types 16 and 18 have been associated with cervical carcinoma

B - There is currently no therapeutic vaccine nor adequate treatment for cervical carcinoma

C - A virus-like particle (VLP) vaccine recently licensed may be ably to prevent new infections with HPV and therefore lower the incidence of cervical carcinoma

D - In cervical carcinoma cells the HPV genome can be found integrated into the chromosome


  A, B, and C only are correct

  A and C only are correct

  B and D only are correct

  D only is correct

  All are correct

5

A 37 year old HIV positive male patient is admitted to hospital because of weight loss and an increasingly frequent non-productive cough and breathlessness. Chest X-ray reveals an interstitial pneumonia. Which one or more of the following microorganisms are likely causes of his lung problems?

A - Klebsiella pneumoniae

B - Pneumocystis jiroveci (carinii )

C - Streptococcus pneumoniae

D - Mycobacterium avium-intracellulare (MAC)


  A, B, and C only are correct

  A and C only are correct

  B and D only are correct

  D only is correct

  All are correct


Both Pneumocystis and the bacteria which make up the Mycobacterium avium complex (MAC) cause an interstitial pneumonia, and have been well-documented to be associated with opportunistic infections in HIV-AIDs, because of the requirement for CD4 T cell activity for the control of these infections.

6

Which one of the following statements are correct regarding the characteristics of Chlamydia trachomatis?


  It appears Gram negative in a Gram stain

  Its outer membrane resembles that of a Gram negative bacterium

  It requires culture on enriched medium for its growth

  It can be treated using the same antimicrobial agents as Neisseria gonorrhoeae

  Antimicrobial agents target the infective form of the bacterium


1 is incorrect: Chlamydiae do not retain Gram stain reagents because they lack peptidoglycan. 2 is correct. 3 is incorrect: Chlamydiae are obligate intracellular organisms and require living cells to grow. 4 is incorrect: Treatment of chlamydial infection requires antimicrobials which access host cells, such as the erythromycins and tetracyclines. 5 is incorrect: The infective form of the agent is non-replicative, thus it is unaffected by antibiotics.