Chapter 8- Infectious Diseases

Question 1

In developed countries, infectious diseases are an important cause of death among which populations?

Answer 1

Elderly

Chronic disease

Immunosuppressed

Question 2

What types of infections are caused by commensal organisms?

Answer 2

Opportunistic

Question 3

What are the different routes of entry of infectious organisms?

Answer 3

Breaching of epithelial surfaces

Inhalation

Ingestion

Sexual transmission

Vertical transmission

Question 4

What organisms are more likely to breach respiratory, GI and GU tract epithelium?

Answer 4

Virulent organisms which can damage/penetrate the mucosa

Question 5

What types of organisms are more likely to cause skin infections?

Answer 5

Less virulent organisms that enter through injury

Question 6

What are the three modes of vertical transmission?

Answer 6

1. Placental-fetal
2. At birth
3. Postnatal (milk)

Question 7

What are examples of host defences and how they provide resistance to infectious organisms?

Answer 7

Skin- thick, low pH, fatty acids

Respiratory system- macs, mucocilliary clearance, IgA

GI system- acidic pH, mucous, enzymes, bile, IgA, normal flora, defensins

UG tract- flushing, acidic pH

Question 8

What are defensins?

Answer 8

Innate protection

Bind microbes membrane and form pores that cause their death

Question 9

How do microbes evade the immune system?

Answer 9

Antigenic variation (hard to recognize)

Resistance to antimicrobial peptides

Resistance to killing by phagocytes

Evasion of apoptosis

Manipulation of host metabolism

Resistance to cytokines, chemokines, complement-mediate defences

Evasion of recognition (CD4 and 8)

Latent infection

Question 10

How do microbes cause host damage?

Answer 10

Direct cell death

Release of toxins

Release of enzymes (tissue and vessel breakdown)

Induction of immune response (pyogens)

Question 11

What are the possible mechanisms of bacterial injury?

Answer 11

Mobile genetic elements- bacteriophages and plasmids

Adhesion to host cells- adhesins and pili

Host cell entry- proteins and opsonization

Toxins/super Ags

Question 12

What are bacteriophages?

Answer 12

Viruses against bacteria that can transfer genes that increase virulence

Question 13

What are plasmids?

Answer 13

DNA rings that can transfer Ab resistance

Question 14

How does opsonization help bacteria enter host cells?

Answer 14

Complement activation leads to engulfment, cells are able to replicate within the immune system

Question 15

What toxins do gram positive and negative bacteria produce?

Answer 15

Gram neg- endotoxins (cell wall)

Gram pos- exotoxins (secreted)

Question 16

What are super antigens?

Answer 16

Toxins stimulated by s large T cell response

Question 17

What are the mechanisms of viral injury?

Answer 17

Tropism- infection of specific cell types

Direct cytopathic effects

Anti-viral immune response- infected cells are destroyed

Transformation of infected cells- processes are hijacked

Question 18

What do viruses produce when they take over cellular production?

Answer 18

Degradative enzymes

Toxic proteins

Trigger apoptosis

Misfolded proteins

Question 19

What are some common viruses and their characteristics?

Answer 19

Viral hemorrhagic fever- animal/insect vector, Ebola, hanta

Varicella-Zoster- latency in ganglia

CMV- affects immunocompromised, transplant patients and neonates, owl eye inclusions

HIV

Transforming viruses- EBV to Burkitt lymphoma and nasopharyngeal carcinoma, HPV to cervical cancer, HTLV-1

Question 20

What are the characteristics of Staph aureus?

Answer 20

Gram pos clusters

Skin infections

Food poisoning

TSS

MRSA

Question 21

What are the characteristics of Strep?

Answer 21

Infects skin, lung, heart valves and the oropharynx

Gram pos chains

Necrotizing faciitis

Rheumatic fever

Pneumonia

Scarlet fever

VRE

Question 22

What are the characteristics of Neisseria meningitidis?

Answer 22

Gram neg diplococci

Acid fast (waxy cell wall)

Meningitis

Question 23

What are the characteristics of Mycobacterium tuberculosis?

Answer 23

Gram pos rods

Acid fast

Delayed hypersensitivity

Necrotizing granulomas (caseating)

Question 24

How does tuberculosis progress?

Answer 24

Primary complex or latent lesions become progressive secondary Tb which disseminates (miliary Tb)

Localized caseating, destructive lesions (often pulmonary)

Question 25

What is Ghon complex?

Answer 25

Combination of parenchymal lung lesion and nodal involvement

Question 26

What are the characteristics of Clostridium?

Answer 26

Anaerobic gram pos bacilli

Cellulitis

Gas gangrene

C. diff- colectomy with pseudomembranes, often with long term Ab use

Question 27

What are the characteristics of Coccidiodmycosis?

Answer 27

Soil dwelling fungus

Inhalation

Question 28

What are the characteristics of Cryptococcus?

Answer 28

Yeast causing disease in immunocompromised

Inhalation

Wild bird droppings

Question 29

What are prions and their characteristics?

Answer 29

Misfolded proteins (beta pleated sheet) that resist degradation

Encourage the misfolding of other proteins

Cause CJD- transmissible spongiform encephalopathies

Question 30

What form of CJD is most common?

Answer 30

Sporadic

Question 31

What is required for the diagnosis of infectious disease?

Answer 31

Culture

Serologic ID

Molecular tests

Special stains

Question 32

What are the different kinds of special stains and what are they used for?

Answer 32

Gram- all

Acid fast/ZN- mycobacteria and nocardiae

Silver- fungi, legionella, pneumocystis

PAS- fungi, amebae

Mucicarmine- cryptococci

Giemsa- H. pylori, Campy, malaria, leishmaniae