Skin and Eye Infections

Infections of the Skin and Eye

Anatomy

Anatomy of the Skin

  • The skin is the largest organ of the human body, covering 16-22 square feet.

  • It harbors around 1 trillion microbes.

  • Functions of the skin include:

    • Regulating body temperature.

    • Preventing dehydration.

    • Acting as a physical barrier against microbes, protecting deeper tissues.

Structure of the Skin
Epidermis:

  • Consists of the following layers:

    • Stratum Corneum:

    • Composed of dead keratinocytes that are shed every 2 weeks.

    • Keratinocytes:

    • Produce keratin, which is a tough fibrous structural protein.

    • Stratum Basale:

    • Contains stem cells and melanocytes which produce melanin, giving skin its color.

    • Langerhans Cells:

    • Located in the stratum spinosum, remove foreign antigens by transporting them to nearby lymph nodes.

Dermis:

  • Primarily composed of connective tissue including:

    • Mast cells, macrophages, and fibroblasts.

    • Houses blood vessels, nerves, hair follicles, and sweat glands.

Hypodermis (Subcutaneous Layer):

  • Also known as superficial fascia.

  • Composed largely of adipose and connective tissues.

Mucous Membranes

  • Composed of epithelial tissue that lines the internal body surfaces.

  • Continuous with the skin at various points (e.g., inside of eyelids, gastrointestinal tract, urogenital tract).

  • Acts as a barrier to protect underlying structures; metaphorically referred to as "skin for inside the body."

Anatomy of the Eye

External Eye Structure

  • Includes features such as:

    • Eyelids

    • Cornea

    • Pupil

    • Parts of the sclera

Internal Eye Structure

  • Comprises:

    • Retina

    • Macula

    • The remainder of the sclera

Viral Infections

Case Study: Moyo’s Macular Rash

  • A case involving a young mother from Zimbabwe whose unvaccinated son, Moyo, exhibited signs of measles, underscoring the consequences of vaccination refusal.

  • Symptoms: High fever, confusion, seizures, and a rash indicative of measles.

    • The outbreak resulted in the death of several children, leading health officials to intervene and implement compulsory vaccinations.

Hemorrhagic Rashes

  • Rash: A change in color and texture of the skin.

    • Exanthem: Widespread rash with systemic symptoms (fever, malaise).

    • Enanthem: Rashes on mucous membranes.

  • Rashes can be infectious or non-infectious, where infectious rashes can derive from:

    • Toxins produced by organisms.

    • Damage by the organisms.

    • Immune responses.

Types of Rashes:

  • Macular: Flat segments, less than 1 cm.

  • Papular: Small, solid, elevated lesions.

  • Pustular: Papules filled with pus.

  • Maculopapular: Reddened papules.

  • Vesicular: Small blisters on the skin.

Measles (Rubeola)

  • Characteristics: Negative-sense, single-stranded RNA virus.

  • Symptoms:

    • Prodromal period: High fever (40°C/105°F), conjunctivitis, and Koplik’s spots.

    • Progressive development of a maculopapular rash.

  • Complications:

    • Myocarditis, pericarditis, acute disseminated encephalomyelitis (ADEM), and subacute sclerosing panencephalitis (SSPE), notable appearing 7-10 years post-infection.

  • Transmission: Through respiratory droplets and direct contact, with a contagious period of 8-10 days.

  • Diagnosis: Based on clinical presentation and serology tests.

  • Treatment: Symptomatic management; antiviral ribavirin for immunocompromised patients.

  • Prevention: MMR vaccine recommended as a routine childhood vaccination.

German Measles (Rubella)

  • Characteristics: Positive-sense, single-stranded RNA virus.

  • Symptoms: Low fever, maculopapular rash starting on head, spreading across the body; lymphadenopathy primarily in head and neck.

  • Complications: Congenital rubella syndrome, risks in immunocompromised individuals.

  • Transmission: Direct contact, virus replicating in lymph nodes.

  • Diagnosis: Clinical presentation and confirmatory tests such as qRT-PCR.

  • Prevention: MMR vaccine as part of routine immunization.

Principles of Special Infections

Fifth Disease (Erythema Infectiosum)

  • Causative Agent: Human parvovirus B19, a non-enveloped, single-stranded DNA virus.

  • Transmission: Via the respiratory tract.

  • Symptoms: Mild fever, joint pain, flu-like symptoms, and characteristic "slap cheek" rash.

  • Stages of Rash:

    • 1st Stage: Slap cheek rash.

    • 2nd Stage: Papular enanthem on the palate.

    • 3rd Stage: Maculopapular rash on limbs.

Roseola Infantum

  • Characteristics: Sudden onset of high fever (over 40°C/104°F) followed by a maculopapular rash.

  • Primarily affects children under 3; caused by human herpesvirus 6 and 7.

  • Transmitted via respiratory secretions; complications are rare.

Burn Wound Infections

  • Common in patients with extensive burns (>10% surface area) leading to higher infection risk.

  • Pathophysiology includes impaired immune responses and increased susceptibility to infections from skin flora (e.g. Staphylococcus, Pseudomonas).

Gangrene Classification

  • Dry Gangrene: Results from compromised blood supply; seen in conditions like frostbite.

  • Wet Gangrene: Caused by infections leading to tissue necrosis, often associated with Clostridium species.

Gas Gangrene

  • Caused by Clostridium perfringens; characterized by rapid tissue necrosis and gas production, often in traumatic wounds.

Eye Infections

Overview

  • Eye infections can be classified primarily into conjunctivitis and keratitis.

  • Conjunctivitis: Involves inflammation of the conjunctiva.

    • Can be infectious (bacterial, viral) or non-infectious (allergic).

Viral Eye Infections

  • Herpes Simplex Virus: Major cause of keratitis; treated with antivirals such as acyclovir.

  • Herpes Zoster Ophthalmicus: Can occur from shingles affecting the ophthalmic nerve, often requiring systemic antivirals.

Bacterial Eye Infections

  • Include infections such as bacterial conjunctivitis and serious cases involving Chlamydia trachomatis, which necessitate preventive treatment for newborns.

Fungal Eye Infections

  • Generally involve damaged corneal epithelium; identified through culturing and treated according to depth of infection (superficial vs invasive).

  • Acanthamoeba Keratitis: Associated with contact lenses, leads to severe inflammation and visual loss if untreated; managed through prolonged antiseptic treatment.

Portals of Entry/Exit

Skin:

  • Entry: Through cuts, abrasions, burns; via hair follicles and sebaceous glands, particularly in diabetes.

  • Exit: Infected liquid drainage, shed skin cells, vesicular fluid from viral infections.

Eyes:

  • Entry: Through direct contact, contaminated water, trauma.

  • Exit: Tears and eye discharge.