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DMF Week 7 SAQ

1

Which one or more of the following statements is correct?

The transcutaneous route of viral infection of humans is exemplified by:

A - papilloma viruses which enter the skin via abrasions

B - hepatitis A virus which enters via use of contaminated needles

C - hepatitis B virus which can enter via body piercing and tattooing

D - dengue virus which is spread by the bite of a racoon


  A, B, and C, are correct

  A and C are correct

  B and D are correct

  D is correct

  All are correct


1 is incorrect. 2 is correct: Papilloma viruses typically infect broken skin and mucous membranes. HBV is transmitted by blood and secretions, which may be transmitted by contaminated needles. 3 is incorrect: Whilst HAV can be transiently found in the blood, it has not been reported to be transmitted in this way. Dengue virus is transmitted by the bite of a mosquito.

2

Which one or moreof the following statements about interferons is correct?

A - Interferons are of type I and type II which bind to the same receptor

B - Type II interferons (IFNgamma) are produced by T cells and NK cells

C - Type I interferons (IFNalpha and beta) are produced by NK cells

D - Type I interferons (IFNalpha and beta) activate NK cells


  A, B, and C, are correct

  A and C are correct

  B and D are correct

  D only is correct

  All are correct


1 is incorrect. 2 is incorrect: Type I and II interferons bind different receptors on target cells. NK cells do not produce interferon alpha or beta. 3 is correct: NK cells produce IFNgamma but are activated to do so by IFNalpha and beta produced by infected epithelial cells.

3

Which one of the following statements about the ability of viruses to cause damage to host cells and thus disease is incorrect?


  Viruses may cause damage to host cells by inhibiting the host cell protein and nucleic acid synthesis.

  Viral infection may induce transformation in infected cells.

  Some viral rashes, e.g. in measles virus infection, are due to T cell mediated pathology.

  Infection with some viruses can temporarily or permanently suppress host cell responses leading to an increased susceptibility to infections with other microorganisms.

  Young children are more susceptible than adults to damage due to immunopathogenic mechanisms.


This is the correct answer to this question since this statement is incorrect. Infection in adults is typically associated with immunopathology. Thus infection with HBV in young children is typically asymptomatic, whereas infection with HBV in adults may result in liver damage due to the immune response generated against HBV.

4

Which one of the following statements about the herpes virus family is incorrect?


  Some members of the herpes virus family cause congenital infection.

  All members of the herpes virus family cause latent infection.

  Members of the herpes virus family can alter antigen processing and presentation via the Class I MHC pathway

  The herpes simplex virus genome may be maintained as an episome in neurones, resulting in latency.

  Patients will clear herpes simplex virus infection if they can produce specific anti-herpes simplex antibodies.


1 is correct: CMV (cytomegalovirus) is an important cause of congenital infection. Varicella zoster virus has also been reported to be a rare cause of congenital infection. HSV more commonly causes perinatal infection. 2 is correct. 3 is correct: This statement describes one of the ways that HSV evades the immune system 4 is correct. 5 is incorrect: The antibodies produced in response to the infection cannot affect the latent phase.

5

Baby S.T. is three days old and is in the neonatal unit, having been born at 32 weeks gestation after a prolonged labour. She weighs 2.1kg. She has become irritable, is feeding poorly and has become hypoxic. A paediatrician collects blood and CSF for culture. Which one or more of the organisms listed below is a likely cause of this baby’s illness?

A - Streptococcus agalactiae

B - Listeria monocytogenes

C - E. coli

D - Neisseria meningitidis


  A, B, and C, are correct

  A and C only are correct

  B and D only are correct

  D only is correct

  All are correct

6

The organism grown from blood cultures is a Gram negative bacillus, which grows on MacConkey agar as a large (2 – 3mm diameter) lactose fermenting colony.

On the basis of the above results, which one of the organisms listed below is a likely cause of this baby’s illness?


  Streptococcus agalactiae

  Listeria monocytogenes

  Pseudomonas aeruginosa

  E. coli

  Neisseria meningitidis


1 is incorrect: S. agalactiae is a Gram positive coccus 2 is incorrect: L. monocytogenes is a Gram positive bacillus 3 is incorrect: Whilst Pseudomonas aeruginosa is a Gram negative bacillus, it is a rare cause of neonatal sepsis. 4 is correct: E. coli is a Gram negative bacillus, and is a common cause of neonatal sepsis. 5 is incorrect: N. meningitidis is a Gram negative coccus and is more typically associated with septicaemia and meningitis in an older age group.

7

Which one of the statements below regarding the agents which cause congenital and perinatal infections is correct?


  Neonatal infections with HSV are predominantly contracted when the virus crosses the placenta in the last two weeks of gestation and infects the baby in utero.

  Neonatal infections with hepatitis B virus result in jaundice in the newborn baby.

  Infections with Group A streptococci are the commonest cause of neonatal sepsis.

  Women infected by Chlamydia trachomatis may not have an overt genital discharge.

  Congenital infection by rubella virus is typically seen with equivalent frequency at all stages of gestation.


1 is incorrect: Babies typically contract HSV during delivery. 2 is incorrect: Jaundice is a reflection of liver damage which is due to the immune response against HBV. This response is suppressed in young children infected with HBV. 3 is incorrect. 4 is correct: Chlamydial infection in women is often asymptomatic. 5 is incorrect: Damage caused by rubella virus during pregnancy typically occurs when the virus infects the foetus in the first trimester of gestation.