Infections

Question 1

Explain the difference between primary and secondary immunodeficiency (2)

Answer 1

Primary immunodeficiencies are genetic defects of the immune system that result in impaired immune function. The defects are present from birth. Secondary immunodeficiencies are acquired – see below.

Any 4 of: HIV infection, Haematological malignancies (esp. leukaemias), Chemotherapy for cancer, Certain autoimmune diseases, Immunosuppressive drugs (e.g. for transplantation, corticosteroids), Malnutrition, Diabetes, Extremes of age. Note: “Stress” was accepted but is a rather marginal cause of immunodeficiency.

Question 2

List four (4) causes of secondary immunodeficiency (2)

Answer 2

Any 4 of: HIV infection, Haematological malignancies (esp. leukaemias), Chemotherapy for cancer, Certain autoimmune diseases, Immunosuppressive drugs (e.g. for transplantation, corticosteroids), Malnutrition, Diabetes, Extremes of age. Note: “Stress” was accepted but is a rather marginal cause of immunodeficiency.

Question 3

State what the definitive treatment for Severe Combined Immunodeficiency Syndrome is. Give a reason for this (1)

Answer 3

Bone marrow transplant/ haemopoetic stem cells (½). Because all stem cells originate in the bone marrow (½)

Question 4

Define the term “opportunistic infection” (2)

Answer 4

Not usually capable of causing disease in healthy individuals (1) as it is of low virulence (1)

Question 5

Name two (2) fungal organisms that can typically cause lung infection in immuno-compromised patients (2)

Answer 5

Aspergillus species, Pneumocytis jirovercii

Question 6

Outline the role that normal/indigenous flora plays in the human body (5)

Answer 6

Variety of organisms (½), associated with particular ecological niche (½)

Helps maintain environment (½) and prevent infection with other organisms (½)

Occupy epithelial surfaces (1)

Compete for essential nutrients (1)

Secrete inhibitory substances ‘bactericidins’ that inhibit/kill pathogens (1)

Question 7

Define mucositis associated with malignancies and briefly explain how it is associated with infection (3)

Answer 7

Chemotherapy/radiotherapy causes damage to the integrity of mucosa with inflammation (1), this may cause translocation of GIT bacteria (1) thus leading to systemic infection (1)

Question 8

State the term used for infections that are more likely to occur in an immunocompromised patient. Name three (3) such infections that are commonly seen in South African patients (2)

Answer 8

Opportunistic infections (½) TB, cryptococcal infection, pneumocystis, toxoplasma, CMV (½ each)

Question 9

Define the term “opportunistic infection” (2)

Answer 9

An infection caused by an organism that seldom if ever causes infection in an immunocompetent person, but can cause infection in people whose immune systems are not functioning normally.

Question 10

Define the term “opportunistic pathogen” (2)

Answer 10

Not usually capable of causing disease in healthy individuals (1) as it is of low virulence (1)

Question 11

Name in full three (3) opportunistic pathogens (NB), as well as an appropriate agent for the treatment of the organism (4½)

Answer 11

Pneumocstis jirovecii (carinii)  Cotrimoxazole

Cryptococcus neoformans  Amphotericin B, fluconazole

Toxoplasma gondii  Cotrimoxazole

Mycobacterium avium-intracellulare  Clarithrpmycin, ethambutol

Cryptosporidium parvum  No specific therapy, but restoration of immune function important e.g. with ARVs)

Isospora belli  Cotrimoxazole

Question 12

Name one typical bacterial (full name) and fungal (mould) opportunist typically found in patients with (2)

Answer 12

Pseudomonas aeruginosa (1), Aspergillus spp. (1)

Question 13

The Herpes virus family as a whole are a common cause of opportunistic disease. Briefly explain why this is so (2)

Answer 13

These viruses are ubiquitous (almost everyone is infected). They cause life-long latent infections and can reactivate in the face of immunosuppression (and other stresses).

Question 14

Members of the herpesvirus family commonly cause disease in immunosuppressed patients. Explain why this happens despite measures to prevent exposure to pathogens (2) (NB)

Answer 14

Herpes virus infections are common and once individuals have been exposed, the virus establishes a lifelong latent infection. They commonly reactivate in immunosuppressed patients. Reactivation in an immunosuppressed patient may be associated with life threatening infection.

Question 15

List three (3) herpesviruses and name a complication that each virus can cause in an immunosuppressed patient (3) (NB)

Answer 15

VZV  Shingles

CMV  Retinitis, encephalitis, enteritis, etc

EBV  Pre-malignant lymphoproliferative disorders, non-hodgkin’s lymphoma

HHV8  Kaposi sarcoma

Question 16

List two (2) serious cytomegalovirus infections causing end-organ disease in immunocompromised patients (2x1 = 2)

Answer 16

Interstitial/ hypoxic pneumonia, Retinitis, Gastrointestinal ulceration, Neurological disease

Question 17

Certain malignancies are common in HIV infection. Outline the role that HIV plays in their pathogenesis (3)

Answer 17

HIV is not oncogenic. It causes immuno-suppression which increases the chances of viral persistence and expansion of persistently infected cells. This increases the chance for infected cells to acquire additional mutations and undergo malignant transformation.

Question 18

Despite his very high white blood cell count, a leukaemia patient may still be susceptible to infections. Briefly explain why this is so (2)

Answer 18

He has abnormal white blood cells, which despite being numerous, do not function normally

Question 19

Define mucositis associated with malignancies and outline how is it associated with infection (2)

Answer 19

Chemotherapy/radiotherapy causes damage to integrity of mucosa with inflammation (1), this may cause translocation of GUT bacteria thus systemic infection (1)

Question 20

Bacteria, fungi and viruses can cause infection in patients following stem cell transplant. State one example of each organism (1½)

Answer 20

Bacteria: Pseudomonas aeruginosa, Fungi: Candida/aspergillus, Viruses: Herpes simplex/cytomegalovirus

Question 21

Name in full the organism that most commonly causes oral thrush (1)

Answer 21

Candida albicans

Oral cavity, GIT, skin, genital tract

Question 22

This organism is usually a commensal. Outline, using examples, different mechanisms by which this organism can breach host defences and cause clinical disease (1½)/ Describe its pathogenesis (1½)

Answer 22

• If immune system is compromised through chemotherapy, HIV, diabetes, C.albicans may cause local infection
• If normal flora is disturbed through antibiotics, C.albicans may cause local infection
• Trauma, or indwelling devices may result in C. albicans local infection

Question 23

State the full name of the organism most likely responsible for the above condition and state what type of organism it is (2)

Answer 23

Candida albicans, fungus, yeast

Question 24

State what chemotherapeutic agent may be used to treat Ms Jones infection (1) [candida]

Answer 24

Nystatin lozenges, clotrimazole, fluconazole

Question 25

State the full name of the organism most likely to be causing this rash (1)

Answer 25

Candida albicans

Question 26

Name one reason why this yeast infection is present in this patient (1)

Answer 26

The patient is diabetic which is an immunocompromised state

Question 27

Outline why it is particularly common at this site (1)

Answer 27

Moist and warm in a fold area thus ideal for growth of yeasts.

Question 28

Outline how would manage this condition (2)

Answer 28

Topical antifungal like nystatin/ clotrimazole (½) and correct underlying condition (½), keep area dry (½)

Question 29

Diabetes is one factor that predisposes people to Candida infections. Name three (3) other factors that may be associated with candidiasis (1½)

Answer 29

Immunosuppression due to leukaemia or steroids, Catheterisation, Antibiotic therapy

Question 30

Name four (4) anatomical sites or regions where candida may cause a local infection (2) (NB)

Answer 30

Skin (esp skin folds), Nails, Vagina/ vulva, Mouth, Oesophagus

Question 31

Fully names two bacterial organisms that commonly cause infections of the skin, and name an antibiotic used to treat each (3)

Answer 31

Streptococcus pyogenes, penicillin. Staphylococcus aureus, cloxacillin

Question 32

State the full name of the organism that infects the skin producing erythematous lesions with central areas of hypoaesthesia (1)

Answer 32

Mycobacterium leprae

Question 33

Name the stain most commonly used in skin scrapings to detect the organism referred to above (1) [Mycobacterium leprae]

Answer 33

Ziehl Neelsen (modified)