Skin and Soft Tissue Infections Flashcards
What are the functions of the skin?
1) Physical barrier
2) Homeostasis (thermoregulation)
3) Immunological function
How to pathogens enter the skin?
- direct inoculation by penetration with contaminated object.
- Systemic generalised infection that has manifestations on skin
How does Herpes Simplex Virus Cause infection of the skin?
- 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.
What are episomes?
In a latent/dormant infection, Viral DNA exists as episomes. Which later get activated to produce the proteins that cause disease.
What triggers the reactivation of latent HSV ?
- stress
- infection
What are the primary and secondary infections of Herpes implex virus?
Primary:
- usually occurs in infants.
- lesions inside mouth
Secondary:
- affects all ages
- Genital
- weeping, vesicular.
What diagnostic investigations are done for HSV?
PCR is used to detect HSV DNA in the vesicular fluid
What is the treatment of HSV?
Oral lesions e.g.cold sores:
-Topical Acyclovir
Genital Herpes:
-Oral Acyclovir
What virus causes Herpes Zoster?
Herpes Zoster is caused by Varicella Zoster Virus (VZV)
Herpes Zoster = Shingles
What is the other name for Herpes Zoster?
Shingles
What is the primary and secondary manifestations Varicella Zoster Virus?
Primary = Chickenpos
Secondary = Shingles
What are the characteristics of a shingles rash?
weeping, vesicular rash that is distributed in the dermatomal area of the infected nerve.
What is the diagnostic investigation used for Herpes Zoster?
PCR for Varicella Zoster Virus DNA in the vesicular fluid?
How is Herpes Zoster treated?
Herpes Zoster = Shingles
Caused by VZV.
Treatment = aciclovir
What is Molluscum Contagiosum?
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.
What type of infection are the following:
- Impetigo
- Erysipelas
- Cellulitis
- Necrotising Fasciitis
- Gas Gangrene
- Anthrax
Bacterial Infection
What a the common bacteria that cause skin infections?
- Staph. Aureus
- Strep Pyogenes (Group A Strep)
- Haemophilus Inflenzae
- Pasteurella multocida
Is Staph Aureus Gram positive or gram negative cocci?
Staph aureus is a gran positive cocci (clusters)
Staph Aureus produces the following exotoxins:
- epidermolytic toxins A & B,
- Toxic Shock syndrome toxin
- Panton-Valentine leukocidin
What are the implications of these toxins?
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
Streptococcus Pyogenes is …..
a) gram positive cocci in chains
b) gram negative cocci in chains
Strep Pyogenes is a gram positive cocci in chains.
What is Impetigo?
Infections of the epidermis (superficial infection of the skin) that occurs at the site of skin damage.
What are the causative agents of Impetigo?
- Staph Aureus
- Strep Pyogenes
(or both)
Honey crusted lesions is used to describe?
Impetigo
What are the complications of Impetigo?
Epidermolytic toxin production :
- localised = Bullous Impetigo (fluid filled lesions)
- Generalised = Staphylococcal scalded skin syndrome (SSSS) -looks like burnt skin.
What is Erysipelas?
Infection of the dermis.
deeper than Impetigo
What causes Erysipelas?
Strep Pyogenes
How does Erysipelas present?
1) Fever / malaise
2) Well demarcated inflamed lesion
3) red swollen, painful, hot
(mainly on face / shin)
What is cellulitis?
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)
What are the causative agents of Cellulitis?
1) Staph Aureus
2) Strep Pyogenes
3) Pasteurella multocida
4) haemophilus influenza
What causes Anthrax?
Bacillus Anthracis:
a spore forming aerobic gram positive bacillus
What is traditionally a “woolstorers disease”?
Anthrax
What is necrotising fasciiitis?
-Infection of skin and subcutaneous tissues.
Characterised by a dark rapidly spreading necrotic lesion.
What are the causative agents of Type 1 : Polymicrobial necrotising fasciits?
Enteric Gram -negative bacilli and anaerobes.
from lower GI
What are the causative agents of Type 2 Necrotising fasciitis?
Strep Pyogenes
What is the treatment for necrotising fasciitis?
- Surgical removal of necrotised tissue.
- Intravenous antibiotics.
What does clostridium perfringens (anaerobic gram +ve bacillus) cause?
Clostridium perfringens
