Chapter 22: Skin Infections

Biblical Context on Skin Diseases (Leviticus 14)

• The Lord gives regulations for ceremonial cleansing of any diseased person, including skin diseases.

• Role of the Priest:

  • Examine individuals outside the camp.

  • If healed, perform a cleansing ritual using two clean birds, cedar wood, scarlet yarn, and hyssop.

Historical Background

• Howard Ricketts (1902)

  • Appointed to the University of Chicago; researched Rocky Mountain spotted fever (RMSF).

  • Discovered rod-shaped bacteria in patient blood that could transmit disease to animals.

  • Noted that ticks could transmit RMSF without being harmed themselves.

  • Traveled to Mexico for louse-borne typhus research but tragically died from the disease at 39.

  • Identified Rickettsia prowazekii for typhus and Rickettsia rickettsii for RMSF.

• Stanislaus Prowazek died under similar circumstances while investigating the same disease.

Skin as a Barrier

• Functionality of the Skin:

  • Acts as a tough and flexible barrier against pathogen invasion.

  • Susceptible to injuries (cuts, punctures, burns, bites) which can allow pathogens such as Staphylococcus aureus to enter the bloodstream.

  • Infection Example: Sandfly bites can introduce Leishmania, causing leishmaniasis.

Skin Anatomy and Physiology

• Layers of Skin:

  • Epidermis: Outer layer with dead, keratinized cells that flake off.

  • Dermis: Contains nerves, glands, blood, and lymphatic vessels.

  • Subcutaneous Tissue: Composed of fat and supportive cells:

  • Sebaceous Glands: Produce sebum that keeps skin soft and water-repellent.

  • Sweat Glands: Help with thermoregulation and inhibit microbes by creating a salty environment.

• Normal Skin Microbiota:

  • Adapted to the harsh conditions of the skin, utilizing nutrients from sweat/sebum, and producing by-products toxic to pathogens.

  • Types of Normal Microbiota:

  • Diphtheroids in oily regions (e.g., Propionibacterium)

  • Staphylococci, which produce antimicrobial substances.

  • Malassezia, lipid-dependent yeasts.

Bacterial Skin Diseases

• Staphylococcus aureus:

  • Causes hair follicle infections resulting in abscesses and can spread to deeper tissues.

  • Notably virulent due to factors that inhibit phagocytosis and tissue degradation.

• Epidemiology of S. aureus Infections:

  • Common in nostrils; can be carried asymptomatically and transmitted via hands.

  • Often presents in skin wounds or boils.

  • Antibiotic resistance prevalent (e.g., MRSA) necessitating careful treatment and prevention strategies.

Staphylococcal Scalded Skin Syndrome (SSSS)

• Symptoms and Pathogenesis:

  • Starts with redness and fever, followed by blistering.

  • Caused by exfoliatin toxin from S. aureus damaging skin layers.

  • Common in newborns and immunocompromised patients, requiring antiseptic measures and possible antibiotic treatment.

Rocky Mountain Spotted Fever (RMSF)

• Signs and Symptoms:

  • Includes headache, fever, and rash that originates from blood leakage into the skin.

• Causative Agent:

  • Rickettsia rickettsii, a Gram-negative obligate intracellular bacterium transmitted by tick bites (usually requiring 4-10 hours of feeding).

• Pathogenesis:

  • Bacteria invade endothelial cells, replicating and inducing membrane damage leading to widespread symptoms (shock, bleeding, potentially death).

• Treatment and Prevention:

  • Early administration of doxycycline can improve outcomes (low case-fatality rates with treatment).

Viral Skin Diseases

• Varicella (Chickenpox):

  • Caused by Varicella-zoster virus (VZV); progresses through phases from macules to vesicles.

  • Risks include severe complications in adults and immunocompromised patients.

  • Reactivation leads to shingles later in life.

• Rubeola (Measles):

  • Transmitted via respiratory route, symptoms include fever, cough, and distinctive rash.

  • Can cause severe complications and is preventable through vaccination.

Summary Table of Skin Diseases

• Bacterial Skin Diseases:

  • Acne: Propionibacterium acnes

  • Hair Follicle Infections: Staphylococcus aureus

  • SSSS: Staphylococcus aureus

  • Impetigo: Streptococcus pyogenes

  • RMSF: Rickettsia rickettsii

  • Lyme disease: Borrelia burgdorferi

• Viral Skin Diseases:

  • Varicella: Varicella-zoster virus

  • Rubeola: Rubeola virus

• Fungal Skin Diseases:

  • Cutaneous Mycoses: various species inducing conditions like athlete's foot.

Skin Diseases and Their Traits

Scalded Skin Syndrome (Staphylococcus aureus)

• Symptoms: Begins with redness and fever, followed by blistering caused by exfoliatin toxin, damaging skin layers.

• Treatment/Prevention: Requires antiseptic measures and possible antibiotic treatment.

• Transmission: Typically spreads through direct contact with infected individuals or surfaces.

Chickenpox (Varicella Zoster Virus)

• Symptoms: Progresses from macules to vesicles, highly contagious with severe complications possible, especially in adults.

• Treatment/Prevention: Antiviral treatment like acyclovir may be used; vaccination is effective in preventing infection.

• Transmission: Transmitted via respiratory route; highly contagious, spreading through respiratory droplets.

Shingles (Reactivation of Chickenpox)

• Symptoms: Painful rash follows nerve pathways; can lead to complications like postherpetic neuralgia.

• Treatment/Prevention: Antiviral medications such as acyclovir can be utilized; vaccination for chickenpox can decrease the likelihood of reactivation.

• Transmission: Direct contact with fluid from shingles blisters can transmit the virus to those unvaccinated against chickenpox.

Measles (Rubeola Virus)

• Symptoms: Symptoms include fever, cough, and a distinctive rash; severe complications may occur, particularly in vulnerable populations.

• Treatment/Prevention: Preventable through vaccination; supportive care is used for treatment.

• Transmission: Transmitted via respiratory droplets; highly contagious with airborne spread.