Skin Infections Overview

Chapter 22: Skin Infections

Leviticus 14: Cleansing From Defiling Skin Diseases

• Ceremonial Cleansing: Regulations given by the Lord to Moses regarding ceremonial cleansing of diseased persons.

• Role of the Priest: The priest inspects outside of the camp to confirm healing from skin diseases.

• Cleansing Ritual: Involves the use of two live clean birds, cedar wood, scarlet yarn, and hyssop as part of the cleansing process.

Historical Context of Skin Infections

• Howard Ricketts (1902): Appointed to the University of Chicago, studied Rocky Mountain spotted fever (RMSF).

  • Observed rod-shaped bacteria in patients' blood that could transmit diseases through animal injections, but could not be cultured in labs.

  • Identified that certain tick species transmit RMSF.

  • His studies took him to Mexico for louse-borne typhus; he sadly contracted and died from it at age 39.

  • Contribution: Named the RMSF agent Rickettsia rickettsii and the typhus agent Rickettsia prowazekii.

Anatomy and Physiology of the Skin

• Barrier Functions: Skin acts as a barrier to injuries, pathogens, and a regulator of temperature and fluid loss.

• Skin Structure:

  • Epidermis: Outermost layer of dead, keratinized cells, constantly flaking off and replaced.

  • Dermis: Contains nerves, glands, blood vessels; supports skin strength and elasticity.

  • Subcutaneous Tissue: Fat and connective tissues beneath the dermis that support skin.

• Microbial Landscape:

  • Skin's secretions from sweat and sebaceous glands help inhibit microbial growth.

  • Normal Microbiota: Adapted to the skin's environment, competing with potential pathogens. Common groups include Diphtheroids, Staphylococci, and Malassezia.

Bacterial Skin Diseases

Staphylococcus aureus

• Infection mechanism through hair follicles leading to conditions such as boils and abscesses.

• Virulence Factors:

  • Inhibits phagocytosis and allows for attachment, colonization, and tissue destruction.

  • Production of toxins that damage host tissues.

• Epidemiology:

  • Commonly found in nostrils; transmission often occurs through hands and shared objects (fomites).

  • Methicillin-resistant Staphylococcus aureus (MRSA) strains present a challenge due to antibiotic resistance.

• Preventive Measures: Hand hygiene and proper wound care.

Staphylococcal Scalded Skin Syndrome (SSSS)

• Symptoms: Redness, malaise, fever; blisters develop shortly after the onset of redness.

• Causative Agent: Certain strains of Staphylococcus aureus produce the exfoliatin toxin.

• Pathogenesis: Localized infection leads to systemic effects, causing skin peeling and risk of secondary infections. Mostly affects newborns and immunocompromised individuals.

Rocky Mountain Spotted Fever (RMSF)

• Symptoms: Sudden onset of headaches, fever, and a characteristic rash due to blood leakage; may lead to serious complications without treatment.

• Causative Agent: Rickettsia rickettsii, transmitted through tick bites.

• Pathogenesis:

  • Infects endothelial cells of blood vessels, causing inflammation and clots, leading to skin rash and potentially multi-organ damage.

• Epidemiology: Zoonotic disease, sporadically distributed in the Americas.

• Treatment: Doxycycline is effective if administered early. Lack of a vaccine necessitates preventive strategies against tick bites.

Viral Skin Diseases

Varicella (Chickenpox)

• Symptoms: Itchy red spots progress to blisters. More severe in adults.

• Causative Agent: Varicella-zoster virus (VZV), a member of the herpesvirus family.

• Pathogenesis: Enters via respiratory tract; disseminates to skin through the bloodstream, causing rashes. Can reactivate in the form of shingles later in life.

• Epidemiology: Highly contagious, with a significant decline in incidence post-vaccination.

• Prevention: Attenuated chickenpox vaccine; antivirals like acyclovir can aid in treatment.

Rubeola (Measles)

• Symptoms: Fever, cough, conjunctivitis, and a fine red rash. Can lead to severe complications.

• Causative Agent: Rubeola virus, an enveloped RNA virus.

• Pathogenesis: Inhaled viral particles infect the respiratory tract, spreading throughout the body causing a rash via immune response.

• Epidemiology: Humans are the only reservoir; vaccination has significantly decreased incidence.

• Prevention: Attenuated vaccine recommended; no antiviral treatment currently available.

Learning objectives

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

   • Diphtheroids

   • Staphylococci

   • Malassezia

2. The role of normal skin microbiota in health includes:

   • Competing with potential pathogens for resources and space

   • Producing substances that inhibit pathogen growth.
     In disease, an imbalance or overgrowth can lead to infections.

3. Skin diseases caused by:

   • Staphylococcus aureus: Boils, abscesses, and Staphylococcal Scalded Skin Syndrome (SSSS).

   • Varicella Zoster virus: Chickenpox.

   • Rubeola virus: Measles.

4. Causative agents for the following diseases:

   • Scalded Skin Syndrome: Certain strains of Staphylococcus aureus.

   • Chickenpox: Varicella-zoster virus (VZV).

   • Measles: Rubeola virus.

5. Major pathogenic and symptomatic features:

   • Scalded Skin Syndrome: Redness, malaise, fever, and blisters due to exfoliatin toxin leading to skin peeling.

   • Chickenpox: Itchy red spots progressing to blisters; more severe in adults.

   • Shingles: Reactivation of VZV causing painful, blistering rashes.

   • Measles: Fever, cough, conjunctivitis, and a fine red rash; can lead to severe complications.

6. Treatment or preventive measures:

   • Streptococcal diseases: Penicillin or other antibiotics, along with proper wound care.

   • Chickenpox/Shingles: Attenuated chickenpox vaccine; antivirals like acyclovir for treatment of severe cases.

   • Measles: Attenuated vaccine recommended; no antiviral treatment currently available.

7. Major routes of transmission:

   • Chickenpox: Airborne transmission and direct contact with the rash.

   • Shingles: Reactivation from latent infection; direct contact with the rash can transmit the virus to those not immune.

   • Measles: Airborne transmission via respiratory droplets from an infected person.