DMF MSE 3 2011

1

Which one of the statements about how viruses evade the immune system is correct?


  Killing virus infected cells by cytotoxic T cells can be stopped by upregulating MHC class I expression

  Large RNA virsues in particular encode proteins to avoid immune attack

  Killing of virus-infected cells by NK cells can be stopped by recognition of appropriate levels of viral encoded MHC class II analogues

  Killing of virus infected cells by ctytoixic T cells can be stopped by herpesvirsus proteins that interfere with the passage of peptides through TAP

  Killing of virus infected cells by NK cells can be stopped by herpesvirus proteins that interfere w/the passage of peptides through TAP

2

Which one of the following statements about the pathogenesis of particular viruses is correct?


  Arboviruses are usually spread directly from person to person via the bit of an insect

  Hep A, B and C are transmitted by the fecal-oral route

  Poliovirus initially replicates in the tonsils

  Rotavirus compromise the absorptive capacity of the gut by destroying intestinal epithelium as well as secreting cholera toxin

  Rabies virus travels in the blood to the brain causing death

3

The specificity of aciclovir for herpes simplex virus infected cells is due to which one of the options below?


  Drug activation following specific cleavage by HSV protease

  Receptor mediated endoyctosis of acyclovir into HSV infected cells

  High affinity binding to HSV RT

  Intracellular covalent bonding of acyclovir to valine to form a potent prodrug

  Intracellular mono-phosphorylation of acyclovir by HSV thymidine kinase

4

Which one of the following statements is correct concerning the surface glycoproteins of influeza viruses, the HA and NA?


  The NA is cleaved to allow efficient release of the virus

  They both bind to sialic acid

  They exist in many different forms, all of which are present in humans

  They accumulate small mutations over time in a process called antigenic shift

  The HA is cleaved to reveal the fusion peptide necessary for cell attachment

5

Which statements concertning viral hepatitis is INCORRECT?


  The immune response to viral infection causes the pathogensis of viral hepatitis

  Viral hepatitis is caused by viruses that are cytolytic for hepatocytes

  Immunity to hepatitis A virus (HAV) does not protect from hepatitis E virus (HEV)

  Newborn infants rarely develop jaundice following acute hepatitis virus infection

  Hepatitis B or C viruses commonly result in persistent infections

6

Which of the following is correct about HPV?


  Outer capsid proteins of the virus are not produced in the basal layers of the skin

  HPV capsid antigens are not immunogenic and therefore are poor vaccines

  HPV replication requires insertion of the viral genome into the host chromosome

  A vaccine to treat HPV-associated cervical carcinoma will have to induce antibodies to E6 and/or E7 viral proteins

  Most strains of HPV can infect many species of mammals

7

Which statement concerning HIV-1 infection is correct?


  Leads to HIV-1 replication in all cells of immune system

  Causes a serious depletion off CD8 T-cells in first weeks of infection

  Patients enter a period of asymptomatic HIV infection where no new virus is produced

  Cellular RNA polymerase II transcribes an array of novel mutant virus from each individual integrated HIV provirus

  High error rate of HIV-1 RT enzyme promotes escape from drug control

8

A 33 yr old female presented to the Sexual Health Clinic with a 2 day history of dyuria and a yellowish vaginal discharge. A dipstick test of urine showed no abnormal findings.
Urethral and cervical swabs were collected for laboratory investigations.
A Gram stain on the urethral swab, performed in the clinic during the patient's initial consultation, showed moderate numbers of pus cells with numerous intra- and extra-cellular Gram negative diplococci. Which one of the following would be most appropriate for this patient?


  Empirical treatment for Treponema pallidum

  Empirical treatment for Neisseria gonorrhoeae

  Empirical treatment for Chlamydia trachomatis

  Empirical treatment for Neisseria gonorrhoeae and Treponema pallidum

  Empirical treatment for Neisseria gonorrhoeae and Chlamydia trachomatis

9

Mrs CD, a 29 yr old accountant, presented for her first antenatal visit at 10 weeks gestation. Blood was collected for routine antenatal screen for a range of antibodies. The laboratory reported the test results as follows:
Antibodies against:

IgMIgG
Rubella virusNDD (128)
CMVNDND
Toxoplasma gondii
NDD (64) HepBsAgnot donenot done Antigens:
  • Hepatitis B surface Ag detected
  • Hepatitis B e Ag detected


  Mrs CD's foetus is not protected from congenital infection with rubella virus

  Mrs CD is immune to CMV and will not suffer from disease associated with this agent

  Mrs CD's baby should be treated with hepatitis B vaccine and hyperimmune hepatitis B gammaglobulin immediately after birth

  Mrs CD should avoid potential sources of Toxoplasma gondii to reduce the risk of congenital Toxoplasma infection in her foetus

  Mrs CD is immune to Hepatitis B virus and will not suffer from disease associated with this agent

10

Which of the following statements regarding infections diarrhoea is INCORRECT?


  Diarrhoea can contribute to malnutrition by simultaneously increasing loss of food energy and reducing food absorption

  Acute gastroenteritis caused by viruses occurs more frequently in summer and is especially common in less developed countries

  Watery diarrhoea occurs when the volume of fluid entering the colon exceeds the capacity of large intestine to absorb it

  The reason that oral rehydration fluid can be used to treat or prevent dehydration is because sodium ions can be absorbed when coupled with glucose even when the absorption of sodium chloride is blocked.

  Although enterotoxigenic E. coli (ETEC) is the most frequent cause of travellers' diarrhoea, this condition can also be caused by viruses, such as norovirus, and protozoa such as Giardia lamblia

11

Which of following combinations of parasite and its most common mode of acquisition by humans is correct?


  Ascaris lumbricoidies: ingestion of mature embryonated eggs

  Toxoplasma gondii: bite of an infected cat

  Enterobius vermicularis: ingestion of larvae

  Hookworm: penetration of skin of lower extremity by trophozoites

  Plasmodium vivax: injection of gametes by infected mosquitoes

12

Which of the following statements regarding bacterial pneumonia is INCORRECT?


  Legionalla pneumonia can be diagnosed by testing for Legionella antiens in urine

  Pneumococcal pneumonia can be diagnosed by testing for species specific polysaccharide antigens in throat secretions

  Reasonable "best guess" treatment for community acquired pneumonia in an otherwise well person involves the administration of a beta-lactam antibiotic together with a tetracycline or macrolide

  Macrolides are usually effective against many of the aetiological agents of so-called "atypical pneumonia" including Mycoplasma, Chlamydophilia and Coxiella species

  Pneumonia caused by Mycoplasma, Legionella, Chlamydophila and Coxiella species is more often diagnosed serioglocially than by culture

13

A 23 yr old female who returned 9 days ago from 12 months' volunteer work in a remote village in Papua New Guinea, presents to her GP with a 2 day history of fever, malaise and worsening headache. Thick and thin films were prepared from peripheral blood. Malarial parasites were seen in the thick film. The thin film showed a parasite load of approx. 20% with multiple ring forms being observed in several red blood cells. Which one of the following statements is INCORRECT?


  Antimalarial therapy for this infection should include primaquine to treat the latent liver stage

  Transmission of malaria via blood transfusion from this patient is possible

  Infected red blood cells containing mature forms of these malarial parasites may be sequestered in deep tissues

  The high parasite load results from the ability of this speces to infect all stages of red cell development

  The fever results form the malarial parasites inducing the release of TNFα

14

Which of the following statements regarding antimicrobial interactions is INCORRECT?


  Antimicrobial synergy can occur when one drug enhances the uptake of another, e.g. beta-lactams can increase the uptake of aminoglycosides

  Antimicrobial synergy may occur when two different drugs block sequential steps in a metabolic pathway, e.g. the interference of folic acid synthesis by sulphonamides and trimethoprim

  Antimicrobial antagonism may occur when on drug induces the production of an enzyme that hydrolyses the other, e.g. ampicillin can induce the synthesis of a beta-lactamase that hydrolyses piperacillin

  Antimicrobial synergy can occur when a bactericidal drug is combined with a bacteriostatic one, e.g. using penicillin G with tetracycline to treat meningitis

  The combined interactions of two different drugs can be quantified by determining the fractional inhibitory concentration (FIC) index, which will be less than or equal to 0.5 when the drugs are synergistic

15

Which one of following statements regarding the lab diagnosis of tuberculosis disease in a patient with clinical symptoms consisten with pulmonary tuberculosis is correct?


  Mycobacterium tuberculosis typcailly seen as pink stained rods in gram stained smear of sputum from patient

  Diagnosis made mostly on clinical grounds because M. tuberculosis takes too long to grow on routine culture media for culture to be practical use

  M. tuberculosis doesn’t grow on routine culture media because it is highly fastididous and requires anaerobic conditions for growth

  Detection of acid fast bacilli in the Ziehl-Neelsen stain confirms the diagosis of deiase caused by M. tuberculosis and no further tests are required

  Sputum microscopy may be negative in a patients with pulmonary tuberculosis and diagnosis may need to be made on the basis of clinical symptoms, chest X-ray and Quantiferon TB test.