Skin Diseases and Infections Overview

Skin Surface as a Barrier to Invasion

• The skin acts as a tough, flexible outer covering, crucial for protection but also vulnerable to injuries.

  • Types of injuries include cuts, punctures, burns, chemical damage, and bug bites.

  • Damage can allow pathogens entry into the body.

• For example:

  • Staphylococcus aureus can infect surgical wounds, leading to bloodstream invasion.

  • Leishmania species can be introduced through sandfly bites, causing leishmaniasis.

• Skin infections may occur when pathogens are introduced via the bloodstream from other sites.

Functions of the Skin

• The skin serves multiple key functions:

  • Barrier to pathogens: Blocks entry of microorganisms.

  • Temperature regulation: Maintains optimal body temperature.

  • Fluid loss restriction: Prevents dehydration.

  • Environment sensing: Contains receptors sensitive to touch, pain, and temperature.

Anatomy of the Skin

• Epidermis: The outermost layer consisting of flat cells; the outermost cells are dead and filled with keratin, providing waterproofing.

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

• Subcutaneous tissue (hypodermis): Composed of fat and supportive cells.

Skin Microbiota

• Skin's surface is bathed in secretions:

  • Sweat: Evaporates, leaving a salty residue to inhibit microbial growth.

  • Sebum: Oily secretion from sebaceous glands that keeps skin and hair moist, repelling water.

• The normal microbiota is well-adapted to skin's dry, salty, and cool conditions:

  • They utilize nutrients from sweat and sebum, producing by-products that can inhibit other harmful microbes.

  • The breakdown of sebum yields fatty acids toxic to many bacteria.

• Microbial distribution varies by skin region:

  • Drier areas (e.g., back) harbor fewer microbes (~1,000 bacteria/cm²) compared to moist areas like groin/armpit (over 10 million/cm²).

Bacterial Skin Diseases

Staphylococcus aureus

• Contains various virulence factors:

  • Inhibit phagocytosis, allowing attachment and tissue colonization.

  • Produces enzymes that disrupt host tissues and toxins damaging to the host.

• Hair Follicle Infections:

  • Commonly found in nostrils; approximately 20% of healthy adults are continuous carriers.

  • High risk of transmission via direct contact and contaminated surfaces (fomites).

  • Treatment usually involves antibiotics; in severe cases, drainage may be required.

  • Resistance is a concern, with strains like MRSA being prevalent.

Staphylococcal Scalded Skin Syndrome (SSSS)

• Symptoms include redness, malaise, irritability, fever, leading to fluid-filled blisters within 48 hours.

• Caused by strains of Staphylococcus aureus producing exfoliatin toxin, which causes epidermal separation.

• Treatment includes antibiotics and removal of dead skin cells; potential fatality requires prompt intervention.

Rocky Mountain Spotted Fever (RMSF)

• Caused by Rickettsia rickettsii, characterized by symptoms like fever, joint pain, and rash due to blood leakage.

• Transmitted through tick bites, bacteria invade endothelial cells.

• Treatment with doxycycline or chloramphenicol effective; high case-fatality rate if untreated.

Viral Skin Diseases

Varicella (Chickenpox)

• Caused by the varicella-zoster virus (VZV), presents as red spots progressing to blisters.

• More severe in adults; can lead to pneumonia and other complications, higher fatality rates in infants.

• Treatment involves antivirals (e.g., acyclovir) and vaccination.

Rubeola (Measles)

• Symptoms include high fever, cough, and a distinctive red rash; risk of serious complications like pneumonia.

• Caused by the rubeola virus, which suppresses immunity.

• Preventive measures include vaccination; no antiviral treatment.

1. The three major groups of microorganisms making up the normal microbiota of the skin are:

   • Bacteria

   • Fungi

   • Viruses

2. The normal skin microbiota plays a crucial role in health and disease by:

   • Outcompeting harmful pathogens for resources and space, thereby preventing infections.

   • Producing by-products that inhibit the growth of harmful bacteria.

   • Contributing to immune system development and function.

3. Skin diseases caused by:

   • Staphylococcus aureus: Hair follicle infections, Scalded Skin Syndrome (SSSS).

   • Varicella Zoster virus: Chickenpox.

   • Rubeola virus: Measles.

4. Causative agents for the following diseases:

   • Scalded Skin Syndrome: Staphylococcus aureus producing exfoliatin toxin.

   • Chickenpox: Varicella-zoster virus (VZV).

   • Measles: Rubeola virus.

5. Major pathogenic and symptomatic features:

   • Scalded Skin Syndrome: Symptoms include redness, malaise, irritability, fever leading to fluid-filled blisters due to epidermal separation caused by exfoliatin toxin.

   • Chickenpox: Presents as red spots that progress to blisters; more severe in adults and can lead to pneumonia.

   • Shingles: Caused by reactivation of VZV, characterized by painful rash and blisters; typically occurs in older adults or immunocompromised individuals.

   • Measles: Symptoms include high fever, cough, and a distinctive red rash; can lead to severe complications like pneumonia due to immunosuppression.

6. Appropriate treatment or preventive measures:

   • Streptococcal diseases: Treatment usually involves antibiotics.

   • Chickenpox/Shingles: Antiviral medications (e.g., acyclovir) and vaccination are the main preventive measures.

   • Measles: Vaccination is the primary preventive measure; no antiviral treatment is available.

7. Major routes of transmission:

   • Chickenpox: Airborne droplets from infected individuals or direct contact with the blisters.

   • Shingles: Reactivation of the virus in someone who has had chickenpox; can spread through direct contact with the rash.

   • Measles: Airborne transmission through respiratory droplets from coughs and sneezes, or by direct contact with nasal or throat secretions.