skin and eye infections
Presentation Segments Breakdown
Section 1: Skin as an Organ
Skin: Largest organ ( sq ft), serves as a barrier against microbes.
Composed of layers: Epidermis (outermost layer) and Dermis (inner layer).
Epidermis:
Contains keratinocytes (produce keratin for structural integrity and barrier function).
Contains melanocytes (produce melanin, providing pigmentation and UV protection).
Also includes Langerhans cells (immune cells involved in antigen presentation).
Dermis:
Contains blood vessels (supply nutrients), nerve endings (sensory perception), hair follicles, and sweat glands.
Houses various immune cells (e.g., macrophages, mast cells) crucial for defense.
Rashes: Visible changes in skin texture or color; indicators of underlying conditions.
Can be infectious (e.g., bacterial, viral, fungal) or allergic in nature.
Types based on morphology:
Macular (flat, discolored, < cm).
Papular (raised, solid, < cm).
Vesicular (raised, fluid-filled, < cm, e.g., chickenpox).
Pustular (pus-filled, raised).
Bullous (large blisters, > cm).
Section 2: Viral Skin Infections
Measles (Rubeola):
Caused by a paramyxovirus, transmitted via respiratory droplets.
Characterized by Koplik spots (small white spots on buccal mucosa) and a maculopapular rash that spreads from face downwards.
Vaccination (MMR) is key to prevention.
Complications include pneumonia, encephalitis, and subacute sclerosing panencephalitis.
German Measles (Rubella):
Caused by rubella virus, milder than measles but significant for congenital defects.
Primarily affects pregnant women, leading to severe congenital rubella syndrome in neonates (e.g., deafness, cataracts, heart defects).
Fifth Disease (Erythema Infectiosum):
Caused by Parvovirus B19, common in children.
Presents with a distinctive bright red facial rash ("slapped cheek" appearance) followed by a lacy rash on the trunk and limbs.
Chickenpox (Varicella):
Caused by varicella-zoster virus (VZV).
Presents with highly pruritic (itchy) vesicular rashes in various stages of healing.
VZV remains latent in dorsal root ganglia and can re-emerge as Shingles (Herpes Zoster) later in life, often triggered by stress or immunosuppression, causing painful unilateral vesicular rash.
Herpes Simplex Virus (HSV):
HSV-1 typically causes oral herpes (cold sores).
HSV-2 typically causes genital herpes.
Characterized by recurrent vesicular lesions.
Section 3: Bacterial Infections
Staphylococci (Staphylococcus aureus):
A common opportunistic pathogen.
Can cause:
Folliculitis (inflammation of hair follicles).
Furuncles (boils) and Carbuncles (clusters of boils).
Impetigo (superficial skin infection with crusty lesions).
Cellulitis (deeper dermis and subcutaneous tissue infection).
Toxic Shock Syndrome (TSS), a severe systemic illness due to toxin production.
MRSA (Methicillin-Resistant Staphylococcus aureus) is a resistant strain requiring alternative treatments like vancomycin.
Streptococci (Streptococcus pyogenes) (Group A Strep):
Associated with various infections, including:
Impetigo (can be caused by both Staph and Strep).
Erysipelas (a distinct superficial cellulitis with raised, sharp borders).
Necrotizing Fasciitis ("flesh-eating disease") - a severe, rapidly progressing infection of the fascia, requiring prompt surgical debridement and aggressive antibiotic treatment.
Scarlet Fever (rash accompanying strep throat).
Rheumatic Fever (a post-streptococcal complication).
Section 4: Fungal Infections
Tinea (Ringworm):
Caused by dermatophytes (fungi that thrive on keratin).
Defined by body area affected, presenting as annular (ring-shaped) lesions:
Tinea capitis (scalp).
Tinea pedis (athlete's foot).
Tinea cruris (jock itch).
Tinea corporis (body).
Treated with topical or oral antifungals.
Candida (e.g., Candida albicans):
A yeast that is part of normal flora but can cause infections through an imbalance.
Especially common among immunocompromised individuals, those on antibiotics, or with diabetes.
Causes mucocutaneous infections like oral thrush, vaginal yeast infections, and intertrigo (skin fold rash).
Section 5: Special Circumstances Around Skin Infections
Diabetes:
Altered glucose metabolism impairs immune function (e.g., neutrophil dysfunction) and microcirculation, increasing susceptibility to skin infections.
Common pathogens include candidiasis, staphylococcal, and streptococcal infections.
Burns:
Damage to skin results in loss of the primary physical barrier, increasing infection risk.
Compromised local immune response and presence of necrotic tissue facilitate microbial colonization.
Common pathogens include Pseudomonas aeruginosa and Staphylococcus aureus.
Gangrene:
Tissue death due to lack of blood supply, often complicated by bacterial infection.
Particularly gas gangrene caused by Clostridium perfringens, an anaerobic bacterium that thrives in low oxygen environments (e.g., deep wounds).
Characterized by gas production in tissues, requiring urgent surgical debridement and broad-spectrum antibiotics.
Section 6: Eye as an Organ and Eye Infections
Eye Anatomy (relevant to infection):
Conjunctiva: A thin, transparent mucous membrane lining the inner surface of the eyelids and covering the sclera.
Cornea: The transparent outer layer at the front of the eye, crucial for vision, but vulnerable to injury and infection.
Eyelids and Lashes: Provide a physical barrier and protect from foreign bodies and excessive light.
Lacrimal Apparatus: Produces tears containing lysozyme (an antimicrobial enzyme) which lubricate and cleanse the eye.
Common Eye Infections:
Conjunctivitis ("Pink Eye"): Inflammation of the conjunctiva.
Bacterial Conjunctivitis: Often presents with purulent (pus-like) discharge, red eyes, gritty sensation. Highly contagious. Common pathogens: Staphylococcus aureus, Streptococcus pneumoniae, Haemophilus influenzae.
Viral Conjunctivitis: Typically watery discharge, often associated with upper respiratory infections, sensitivity to light. Common pathogens: Adenovirus, Herpes Simplex Virus.
Allergic Conjunctivitis: Itchy, watery eyes, often seasonal, not infectious.
Keratitis: Inflammation of the cornea, more serious due to potential vision loss.
Bacterial Keratitis: Can be severe, often associated with contact lens wear or corneal abrasion. Pathogens: Pseudomonas aeruginosa (especially with contact lenses), Staphylococcus aureus.
Viral Keratitis: E.g., Herpes Simplex Keratitis, can lead to recurrent episodes and corneal scarring.
Fungal Keratitis: Rare, often following trauma involving plant material. Requires specific antifungal treatment.
Acanthamoeba Keratitis: A parasitic infection, typically linked to contaminated contact lens solutions or water exposure.
Blepharitis: Chronic inflammation of the eyelid margins.
Often caused by Staphylococcus species or Demodex mites.
Symptoms include itching, burning, redness, and crusting of eyelashes.
Hordeolum (Stye): An acute localized bacterial infection of an oil gland in the eyelid (e.g., Staphylococcus aureus).
Chalazion: A sterile, chronic granuloma of a meibomian gland, often developing after a hordeolum.
Dacryocystitis: Infection of the lacrimal sac, usually due to nasolacrimal duct obstruction.
Cellulitis of the Eye: Infections around the eye.
Preseptal (Periorbital) Cellulitis: Infection anterior to the orbital septum, usually localized to the eyelids and surrounding skin, less severe.
Orbital Cellulitis: A serious infection posterior to the orbital septum, affecting tissues within the orbit. Often spreads from adjacent sinuses, constitutes an ocular emergency requiring urgent intravenous antibiotics to prevent vision loss or intracranial spread.
Risk Factors for Eye Infections:
Contact lens use (especially poor hygiene).
Ocular trauma or foreign