Microbiology

Question 1

describe the tolerogen effect in HBV

Answer 1

E antigen is a soluble form of HBV core antigen.
E antigen crosses the placenta.
This results in clonal detection of lymphocytes recognising epitopes shared with HBV core antigen.
HBV core is effectively recognised as self antigen.
This leads to chronic infection.

Question 2

describe the usefulness of the markers used for HBV

Answer 2

see blood virus lecture part 1 - slide 18

Question 3

what is the difference between e antigen positive and negative in HBV

Answer 3

e antigen positive:
• High grade infection
• High risk of onward transmission
• e.g. from needle stick 33% risk
• Likely to develop chronic active hepatitis, Cirrhosis and hepatocellular carcinoma

e antigen negative:
• Low grade infection
• Low risk of onward transmission
• e.g. from needle stick < 1% risk
• Not likely to develop clinical effects

Question 4

what is the treatment of HBV

Answer 4

Lamivudine
• Aim is suppression rather than cure
- can develop resistance however

Interferon
• Aim is cure of high grade infection

Transplantation

Question 5

Main route of transmission for HCV

Answer 5

IV drug use

Question 6

Describe the usefulness of markers for HCV

Answer 6

See blood virus lecture 2 slide 6

Question 7

describe treatment of HCV

Answer 7

Interferon and Ribavirin
• Aim is cure of high grade infection

Transplantation
• HCV recurs in graft

Question 8

describe the mechanism of action of HIV

Answer 8

Retrovirus

• Infects immune cells
• CD4 Lymphocytes (TH cells)
• Macrophages
• Causes immunosuppression due to reduction in T cell function
• 2 main subtypes (HIV1 & HIV2 and multiple genotypes)

Question 9

describe some infections that may occur in aids

Answer 9

blood lecture 2 slide 14

Question 10

describe treatment of HIV

Answer 10

Anti‐retroviral therapy (ART):
• Aim is suppression rather than cure
• 14 licenced drugs
- To combat development of resistance

Combination of drugs:
- From 3 main classes:
> Nucleoside Reverse transcriptase inhibitors
> Non‐nucleoside Reverse transcriptase inhibitors
> Protease inhibitors
- 3 drugs used together
- Very successful

Mother to baby transmission can be prevented:
- Caesarian section
• ART to mother and baby
• Avoidance of breast feeding
• Reduces transmission rate from 16% to 1%

Question 11

overview of treatment for HBV HCV and HIV

Answer 11

slide 18 blood lecture 2

Question 12

Name some key agents that cause bacterial diarrhoea

Answer 12

Campylobacter
• Salmonella
• Shigella
• E.coli – various pathogenic types
• Vibrio cholerae

Question 13

name some key agents that cause GI infections from toxin ingestion

Answer 13

Clostridium perfringens
• Bacillus cereus
• Staphylococcus aureus
• Clostridium botulinum

Question 14

name some key agents that cause antibiotic associated diarrhoea

Answer 14

• Clostridium difficile

Question 15

name two viruses that cause go infections

Answer 15

Norovirus

• Rotavirus

Question 16

name two parasites that cause GI infections

Answer 16

• Cryptosporidium

* Giardia

Question 17

name some opportunistic bacteria in HIV/AIDS

Answer 17

Mycobacterium tuberculosis
Pneumocystis, Toxoplasmosis
Cytomegalovirus (CMV), Mycobacterium avium‐intracellulare

see slide 28 of immunodeficiency lecture

Question 18

name some fungi that cause infection in HIV

Answer 18

Pneumocystis
• Candida spp.
• Cryptococcus neoformans

Question 19

name some parasites that cause infection in HIV

Answer 19

• Cerebral toxoplasmosis

* Cryptosporidiosis

Question 20

name some bacteria that cause infection in HIV

Answer 20

Mycobacterium avium intracellulare
Mycobacterium tuberculosis
Salmonella

Question 21

name some viruses that cause infection in HIV

Answer 21

• CMV
• Herpes simplex virus
• Human HerpesVirus 8

Question 22

describe the diagnosis presentation and treatment of Pneumocystis pneumonia (PCP) in HIV patient

Answer 22

Diagnosis:
- Silver stain/monoclonal antibody detection in BAL or biopsy
• PCR on bronchial lavage

Presentation:
• Non productive cough, dyspnoea, fever
• Perihilar infiltrates
• May progress – severe respiratory distress
• Extrapulmonary infection

Treatment
• High dose cotrimoxazole
• ICU usually required

Question 23

cause of cerebral toxoplasmosis

Answer 23

T. gondii

Question 24

describe infection in healthy and advanced HIV for cerebral toxoplasmosis

Answer 24

Infection in Healthy hosts:
• Protozoal infection, usually asymptomatic (50% infected by middle age) or glandular fever‐like illness
• Zoonosis: from cats

Presentation in advanced HIV:
• Main cause of focal CNS lesions
• Note ring enhancement
• Pneumonitis and chorioretinitis also occur

Question 25

How are infections prevented in HIV

Answer 25

• CD4 count boosted by HAART (Highly Active AntiRetroviral Therapy) → fewer opportunistic infections

As CD4 count falls prophylaxis is offered for:
• Pneumocystis (co‐trimoxazole)
• Mycobacterium avium intracellulare (rifabutin)
• CMV (ganciclovir)

Question 26

name two opportunistic fungal infections in neutropenia

Answer 26

• Aspergillus fumigatus

* Candida albicans

Question 27

Describe management of sepsis in neutropenia

Answer 27

Empirical therapy:
• Febrile neutropenics cannot await culture results
• URGENT bactericidal broad‐spectrum agents
• Anti‐pseudomonal penicillin + aminoglycoside
• Add vancomycin/teicoplanin (for resistant Gram‐positive bacteria), if no improvement
• Then antifungal if still no improvement
• Other supportive measures (oxygenation, circulatory support, etc.) are CRITICAL

Question 28

name two common infectious agents in burn patients

Answer 28

• Infections with Pseudomonas aeruginosa and Staphylococcus aureus common
• Can spread to bloodstream

Question 29

name two infections pregnant women are at more risk of

Answer 29

1. Ascending UTI

2. Listeria monocytogenes (a Gram‐positive bacillus)