Skin and Soft Tissue Infections

Question 1

What are the functions of the skin?

Answer 1

1) Physical barrier
2) Homeostasis (thermoregulation)
3) Immunological function

Question 2

How to pathogens enter the skin?

Answer 2

• direct inoculation by penetration with contaminated object.
• Systemic generalised infection that has manifestations on skin

Question 3

How does Herpes Simplex Virus Cause infection of the skin?

Answer 3

• Vesicles containing the virus rupture.
• ulcers form around the mouth (HSV1), genital warts (HSV2)
• Virus enters via sensory nerve endings and migrates to the dorsal root ganglion where it lies dormants.
• Virus gets reactivated and migrate out to nerve endings to cause ulcers.

Question 4

What are episomes?

Answer 4

In a latent/dormant infection, Viral DNA exists as episomes. Which later get activated to produce the proteins that cause disease.

Question 5

What triggers the reactivation of latent HSV ?

Answer 5

• stress

- infection

Question 6

What are the primary and secondary infections of Herpes implex virus?

Answer 6

Primary:

• usually occurs in infants.
• lesions inside mouth

Secondary:

• affects all ages
• Genital
• weeping, vesicular.

Question 7

What diagnostic investigations are done for HSV?

Answer 7

PCR is used to detect HSV DNA in the vesicular fluid

Question 8

What is the treatment of HSV?

Answer 8

Oral lesions e.g.cold sores:
-Topical Acyclovir

Genital Herpes:
-Oral Acyclovir

Question 9

What virus causes Herpes Zoster?

Answer 9

Herpes Zoster is caused by Varicella Zoster Virus (VZV)

Herpes Zoster = Shingles

Question 10

What is the other name for Herpes Zoster?

Answer 10

Shingles

Question 11

What is the primary and secondary manifestations Varicella Zoster Virus?

Answer 11

Primary = Chickenpos

Secondary = Shingles

Question 12

What are the characteristics of a shingles rash?

Answer 12

weeping, vesicular rash that is distributed in the dermatomal area of the infected nerve.

Question 13

What is the diagnostic investigation used for Herpes Zoster?

Answer 13

PCR for Varicella Zoster Virus DNA in the vesicular fluid?

Question 14

How is Herpes Zoster treated?

Answer 14

Herpes Zoster = Shingles
Caused by VZV.
Treatment = aciclovir

Question 15

What is Molluscum Contagiosum?

Answer 15

A skin infection caused by pox virus (aka molluscum contagiosum virus)

• Characterised by raised pearly lesions.
• usually clear relatively quickly.
• doesn’t come back / no latent phase.

Question 16

What type of infection are the following:

• Impetigo
• Erysipelas
• Cellulitis
• Necrotising Fasciitis
• Gas Gangrene
• Anthrax

Answer 16

Bacterial Infection

Question 17

What a the common bacteria that cause skin infections?

Answer 17

• Staph. Aureus
• Strep Pyogenes (Group A Strep)
• Haemophilus Inflenzae
• Pasteurella multocida

Question 18

Is Staph Aureus Gram positive or gram negative cocci?

Answer 18

Staph aureus is a gran positive cocci (clusters)

Question 19

Staph Aureus produces the following exotoxins:

• epidermolytic toxins A & B,
• Toxic Shock syndrome toxin
• Panton-Valentine leukocidin

What are the implications of these toxins?

Answer 19

1) Epidermolytic toxin causes empatigo.
2) toxi shock syndrome toxin causes a T cell mediated immune reaction.
3) Panton-Valentine Leukocidin causes boils and skin abscesses

Question 20

Streptococcus Pyogenes is …..

a) gram positive cocci in chains
b) gram negative cocci in chains

Answer 20

Strep Pyogenes is a gram positive cocci in chains.

Question 21

What is Impetigo?

Answer 21

Infections of the epidermis (superficial infection of the skin) that occurs at the site of skin damage.

Question 22

What are the causative agents of Impetigo?

Answer 22

• Staph Aureus
• Strep Pyogenes

(or both)

Question 23

Honey crusted lesions is used to describe?

Answer 23

Impetigo

Question 24

What are the complications of Impetigo?

Answer 24

Epidermolytic toxin production :

• localised = Bullous Impetigo (fluid filled lesions)
• Generalised = Staphylococcal scalded skin syndrome (SSSS) -looks like burnt skin.

Question 25

What is Erysipelas?

Answer 25

Infection of the dermis.

deeper than Impetigo

Question 26

What causes Erysipelas?

Answer 26

Strep Pyogenes

Question 27

How does Erysipelas present?

Answer 27

1) Fever / malaise
2) Well demarcated inflamed lesion
3) red swollen, painful, hot

(mainly on face / shin)

Question 28

What is cellulitis?

Answer 28

Infection of skin and subcutaneous tissues.
It is a diffuse inflammed lesion so its difficult to see the margins.

(unlike Impetigo and Erysipelas which are well demarcated)

Question 29

What are the causative agents of Cellulitis?

Answer 29

1) Staph Aureus
2) Strep Pyogenes
3) Pasteurella multocida
4) haemophilus influenza

Question 30

What causes Anthrax?

Answer 30

Bacillus Anthracis:

a spore forming aerobic gram positive bacillus

Question 31

What is traditionally a “woolstorers disease”?

Answer 31

Anthrax

Question 32

What is necrotising fasciiitis?

Answer 32

-Infection of skin and subcutaneous tissues.

Characterised by a dark rapidly spreading necrotic lesion.

Question 33

What are the causative agents of Type 1 : Polymicrobial necrotising fasciits?

Answer 33

Enteric Gram -negative bacilli and anaerobes.

from lower GI

Question 34

What are the causative agents of Type 2 Necrotising fasciitis?

Answer 34

Strep Pyogenes

Question 35

What is the treatment for necrotising fasciitis?

Answer 35

• Surgical removal of necrotised tissue.

- Intravenous antibiotics.

Question 36

What does clostridium perfringens (anaerobic gram +ve bacillus) cause?

Answer 36

Clostridium perfringens