Diseases of the Skin - Study Notes

Diseases of the Skin

Terms

• Vesicles: Small, fluid-filled blister.
• Abscess: Localized collection of pus surrounded by inflammation.
• Cellulitis: Skin infection due to bacteria; presents as redness or inflammation.
• Myositis: Inflammation of skeletal muscles.
• Necrotizing fasciitis: Inflammation and death of tissue surrounding muscles, tissues, and/or skin (fascia).

Background: Staphylococcus

• Gram-positive.
• Staphylococcus.

Staphylococcus aureus

• Gram positive; staphylococcus

Virulence Factors of Staphylococcus aureus

• Coagulase: Produces clots; blocks infiltration of leukocytes.
• Exfoliative toxin: Separates layers of epidermis.
• Hyaluronidase: Dissolves hyaluronic acid component of connective tissue allowing infection to penetrate deeper tissue.
• Protein A: Binds to Fc portion of Abs & inhibits phagocytosis.
• Toxic shock syndrome toxin (TSST): Superantigen.

Community Acquired MRSA

• Transmission: Direct contact (skin to skin contact) or indirect (via fomites is common).
• Predisposition: Athletes, tissue injury, preexisting primary infections.

Hair Follicle Infections

• Caused by: S. aureus & MRSA.
• Symptoms: Red, swollen, painful to the touch, fever, skin infection has a yellow or white center, lesion filled w/ pus, cellulitis.
• **Classification of Symptoms (all pyogenic infections):
  • Folliculitis: small red bump, some pus
  • Furuncle (boil): Larger area; infection penetrated deeper into subcutaneous tissues; pus produced.
  • Carbuncle: Large area, multiple drainage areas; commonly associated with systemic symptoms.
• Diagnostic Tip: Patient often presents with what they think is a spider bite.
• Pathogenesis: Staph. attach to hair follicle à move down into follicle and sweat glands à inflammation

Outpatient Treatment of Skin & Soft Tissue Infections

1. Drain lesion with syringe.
2. Send wound drainage for culture.
3. Treatment: If + culture: prescribe antimicrobials (i.e., Vancomycin or Doxycycline).

Prevention

• Wash hands! (hexachlorophene soaps).
• Be careful when handling bandages (used to cover skin infection).
• Don’t share towels, razors, needles.

Systemic Infections

• Bacteria can enter bloodstream from site of infection; enter artery & infect vessels within bones ⌦ Osteomyelitis
• Pain & fever usually present
• Blood cultures are mostly +

Scalded Skin Syndrome

• Causative Agent: Staphylococcus aureus
• Transmission: Infection of severed umbilical cord.
• Symptoms: Reddened skin; Skin peels in sheets.
• Pathogenesis: Due to exfoliative toxin
  • 2o infections – Pseudomonas, Candida
• Epidemiology: Most common in the newborn, the elderly, immunocompromised pts.
• Treatment: Antibiotics.
• Prevention: None

‘Flesh-Eating’ Streptococcal Infection

• Causative agent: Streptococcus pyogenes (GAS).

• Symptoms: Skin swelling & muscle pain!, high fever, confusion, shock (can develop in 24 hrs.).

• Pathogenesis: Bacteria produce Exotoxin A (superantigen; can cause shock) and shed M proteins (prevent phagocytosis); proteases destroy tissues & destroy complement.

• Epidemiology: Sporadic cases; predisposing factors: diabetes, cancer, AIDS, surgery.

• Transmission: Indirect contact (infected wounds from break in skin- needles; minor cut or trauma).

• Diagnosis: Skin biopsy & blood work (look for signs of muscle damage) or use Imaging (MRI).

• Treatment: Surgery (debridement= removal of dead tissue) + high doses of penicillin.

• Prevention: Keep wounds clean; it is not contagious.

• 11,000 cases/yr. in the US

• Mortality > 25%

• Can cause:

  • Cellulitis- infection of dermis & hypodermis
  • Myositis
  • Necrotizing fasciitis

• Patients often develop streptococcal TSS

Virulence Factors of Group A, b-hemolytic Streptococcus pyogenes

• Capsule: Protects from WBC’s
• M protein: Prevents activation of complement & inhibits phagocytosis; when shed from bacteria it forms a complex with fibrinogen that activates WBC’s leading to streptococcal TSS
• Hemolysins & Streptolysins: Lyse RBCs & kill neutrophils, respectively
• Hyaluronidase: Dissolves hyaluronic acid component of connective tissue; allows deeper penetration
• Streptokinase: Dissolves blood clots
• Exotoxin A: Superantigen

Chickenpox & Shingles (Zoster Disease)

• Causative Agent: Varicella Zoster Virus (VZV)

Transmission of Chickenpox

• Direct contact: Mucous droplets (sneezing, coughing)
• Indirect contact: Aerosolization of virus (skin lesions)
• Vertical transmission (dangerous during first half of pregnancy)

Pathogenesis

• Virus enters respiratory tract & multiplies in blood
• Virus damages cells: line blood vessels & epidermal cells
• Immune system eliminates virus; except some in nerve cells!
• Disease can be fatal: Varicella pneumonia; during pregnancy

Shingles

• Herpes zoster: From a Greek word that means “belt”
• Refers to localization of shingle lesions along a band of skin
• Lesions are localized along the infected nerve

Shingles: Treatment

• Valtrex (Brand); Acyclovir/Aciclovir (trade)= Cheap!
• Mode of Action: Interferes with DNA Polymerases of viruses in Herpesvirus family
• Inhibits viral replication
• Must take within 24- 48 hrs. of onset of symptoms
• IV use for immunocompromised

Prevention: Varivax

• Live, attenuated vaccine
• It prevents chickenpox in 70-95% of people who get it
• Not recommended for pregnant women
• Dosing: 2 doses
  • First Dose: 12-15 months of age
  • Second Dose: 4-6 years

Vaccine: Shingles (2 options)

• 2007: F.D.A. approved
  • Zostavax: acts as “booster shot” for adults
    • Contains: Live, attenuated VZV
    • Stronger version of Varivax vaccine (14 times more potent)
• 2017 (F.D.A.): Shingrix
  • Subunit Vaccine
  • Contains part of viral spike
  • “preferred” vaccine
• Recommended for those over 50 yrs.

Pseudomonas aeruginosa Infections

Causative agent: Pseudomonas aeruginosa
Can grow in biofilms

• Symptoms: Opportunistic pathogen of burn patients and cystic fibrosis patients
  • Other infections: Skin – “hot tub dermatitis”
  • “Swimmers ear” – otitis externa (inflammation of ear canal): swimming in fresh-water!
• Pathogenesis: Toxins impair wound healing & damage tissues
  • Often grows as a biofilm; can cause “fruity” smell
  • Exotoxin “A”= causes necrosis of tissues (premature cellular death)
  • Makes a blue-green soluble pigment/toxin, pyocyanin: can cause damage to cells & impair the immune system
  • Pyocyanin is a siderophore: compound helps organism collect Iron
• Epidemiology: Common in water & soil ; can be found growing in flower vases & disinfectants
• Treatment: Quinolones
  • Resistant to many antibiotics & disinfectants
• Prevention: Good wound care