Chapter 21 - Skin & Eye Diseases

Epidermis

Thin outer portion of skin; composed of layers of epithelial cells

Keratin

Waterproofing protein coating outer layer of epidermis

Dermis

Inner, thick portion of skin; composed mainly of connective tissue

What does perspiration do?

• Provides moisture and nutrients for growth

• Contains salt that inhibits microorganisms

Antimicrobial peptides

Short proteins in innate immunity that destroy microbes by disrupting their cell membranes

Sebum

Oily secretion by oil glands containing fatty acids that inhibit pathogens

Mucous Membranes

• Line the body cavities open to the exterior

• Tightly packed epithelial cells attached to an extracellular matrix

  • cells secrete mucous

  • some cells have cilia

• Often acidic

• Membrane of eyes washed by tears containing lysozyme

• Often folded to maximize surface area

Normal Microbiota of the Skin

• Resistant to drying and high salt concentration

• Large numbers of gram positive cocci

  • Staphylococci & micrococci

• Areas with moisture have higher populations

  • Metabolize sweat and contribute to body odor

Cutibacterium acnes

Anaerobic bacteria in hair follicles associated with acne

Corynebacterium xerosis

Aerobic bacteria found on skin surface

Malassezia furfur

Yeast that contributes to dandruff

Vesicle

Small fluid-filled blister on skin

Bulla

Large fluid-filled blister

Macule

Flat discolored spot on skin

Papule

Raised lesion on skin

Pustule

Raised lesion containing pus

Exanthem

Widespread skin rash

Enanthem

Rash on mucous membranes

Staphylococci

Spherical gram-positive bacteria; form irregular clusters

Many produce coagulase

• Enzyme that clots fibrin in the blood

• Used to identify types of staphylococci

Staphylococcus epidermidis

• Ninety percent of normal skin microbiota

• Healthcare-associated pathogen

• Produces biofilm on catheters

• Coagulase-negative

Staphylococcus aureus

• Carried in the nasal passages of 20% of the population

• Golden-yellow colonies

• Coagulase-positive

• May produce damaging toxins and cause sepsis

• Avoids host defenses in the skin

  • Secretes proteins and toxins that kill phagocytic cells

• MRSA strains are antibiotic-resistant

Folliculitis (staph)

Infections of the hair follicles

Sty (staph)

Folliculitis of an eyelash

Furuncle (boil) (staph)

A type of abscess; localized region of pus surrounded by inflamed tissue

Carbuncle (staph)

Damage and inflammation of deep tissue from a spreading furuncle

Impetigo (staph)

• Pathogen → Staph aureus

• Portal of entry → Skin

• Symptoms → Crusting (nonbullous) sores, spread by autoinoculation

• Method of transmission → Direct contact

• Treatment → Topical antibiotics

Scaled skin syndrome (staph)

• Bullous impetigo

• Toxin B causes exfoliation

• Pemphigus neonatorum: impetigo of the newborn

Toxic Shock Syndrome (TSS) (staph)

Fever, vomiting, shock, and organ failure caused by toxic shock syndrome toxin 1 (TSST-1) in the bloodstream

Streptococcal Skin Infections

• Gram-positive cocci in chains

• Produce hemolysins that lyse red blood cells

• Beta-hemolytic streptococci often cause disease

  • Streptococci differentiated into groups A through T based on antigenic cell wall carbohydrates

Group A streptococci (GAS) → Streptococcus pyogenes

Eighty immunological types

Produce virulence factors:

• Streptolysins: lyse RBCs

• M proteins: external to the cell wall; allow adherence and immune system avoidance

• Hyaluronidase: dissolves connective tissue

• Streptokinases: dissolve blood clots

Erysipelas (strep)

• S. pyogenes infects the dermal layer of the skin

• Causes local tissue destruction and sepsis

Necrotizing fasciitis (strep)

• “Flesh-eating” disease

• Exotoxin A produced by S. pyogenes acts as a superantigen

Infections by Pseudomonads

Pseudomonas aeruginosa

• Gram-negative, aerobic rod (water)

• Pyocyanin produces a blue-green pus.

• Produces exo- and endotoxins; grows in biofilms

• Pseudomonas dermatitis

  • Self-limiting rash acquired in swimming pools

• Otitis externa

  • “Swimmer’s ear”

• Opportunistic in burn patients

• Resistant to many antibiotics

Buruli Ulcer

Caused by Mycobacterium ulcerans

• Produces the toxin mycolactone

Enters via a break in the skin or an insect bite

Causes deep, damaging ulcers

• May require amputation

Primarily found in western and central Africa

Acne

• Most common skin disease in humans

• Skin cells shed in the hair follicles and combine with sebum

  • Causes blockages

• Sebum formation is affected by hormones, not diet

Comedonal (mild) Acne

Easily treated with topicals

Inflammatory (moderate) Acne

Caused by Propionibacterium acnes

• Metabolizes sebum; fatty acids produce an inflammatory response

Treated with antibiotics and benzoyl peroxide

Nodular Cystic (severe) Acne

Inflamed lesions with pus deep in the skin

Most common route for skin diseases to be transmitted:

Respiratory routes

Warts

• Papilloma → Small skin growths

• Transmitted via contact

• Caused by Papilomavirus

  • more than 50 types

  • some cause cancers

Smallpox (Variola)

• Caused by an orthropoxvirus

• Two forms of the disease

  • Variola major has 20-60% mortality

  • Variola minor has <1% mortality

• Transmitted via the respiratory route, moves into the bloodstream, and infects the skin

• Method of transmission → Aerosol

• Completely eradicated from the human population by vaccination

• Potential bioterrorism agent

Monkeypox

• Pathoe=gen → Monkeypox virus

• Portal of Entry → Respiratory tract

• Related to smallpox

• Endemic to small animals in Africa

• Jumps from animals to humans

• Prevention by the smallpox vaccination

Chickenpox (varicella)

• Pathogen → Herpesvirus varicella-zoster (human herpesvirus 3)

• Transmitted via the respiratory route

• Causes pus-filled vesicles

• Reye’s syndrome: severe complications of chickenpox; vomiting and brain dysfunction

  • Aspirin use increases risk

• Virus becomes latent in the central nerve ganglia

• Prevented by a live attenuated vaccine

  • Breakthrough varicella can occur if previously vaccinated

Shingles (herpes zoster)

• Pathogen → HHV-3

• Reactivation of the latent varicella-zoster virus (chickpox) that moves along peripheral nerves to the skin

  • Due to stress or lowered immunity

• Follows the distribution of affected cutaneous sensory nerves

  • Limited to one side of the body

• Postherpetic neuralgia

• Prevention via the zoster vaccine

• Antiviral drugs may lessen symptoms.

Human herpesvirus 1 (HSV-1) and 2 (HSV-2)

• HSV-1 is spread primarily by oral or respiratory routes

  • 90% of U.S.

  • Remains latent in trigeminal nerve ganglia

  • Outbreaks are triggered by the sun, stress, or hormonal changes

• HSV-2 is spread primarily sexually

  • Remains latent in sacral nerve ganglia (spine)

Herpes gladiatorum (wrestling)

Vesicles on the skin

Herpetic whitlow (doctors and nurses)

Vesicles on the fingers

Herpes encephalitis

Virus spreads to the brain

• Treated with acyclovir

Measles (Rubeola)

• Viral disease transmitted by the respiratory route

• Cold-like symptoms, macular rash

• Pathogen → Morbillivirus

• Method of transmission → Aerosol

• Koplik’s spots

  • Red spots on the oral mucosa opposite the molars

• Prevented by the MMR vaccine (No treatment)

  • Children under 1 year old cannot receive the vaccine.

Rubella

• German measles

• Pathogen → Rubivirus

• Macular rash and light fever

• Method of transmission → Aerosol

• Transmitted via the respiratory route; 2- to 3-week incubation

• Prevented by the MMR vaccine (No treatment)

  • Not recommended for pregnant women

Fifth Disease (erythema infectiosum)

• Pathogen → Human parvovirus B19

• Mild flulike symptoms; “slapped-cheek” facial rash

• Method of transmission → Aerosol

• No treatment

Roseola

• Roseolovirus (HHV-6, HHV-7)

• Respiratory tract

• High fever; body rash; recovery within 1 to 2 days

• Method of transmission → Aerosol

• No treatment

Hand-foot-and-mouth Disease

• Pathogen → Enteroviruses

• Spread via mouth mucous or saliva (children)

• Fever and sore throat; rash on hands, feet, mouth, and tongue

• Method of transmission → Aerosol

• No treatment

Mycosis

Fungal infection of the body

Cutaneous Mycoses

• Colonize the hair, nails, and outer epidermis

• Metabolize keratin

Dermatomycoses

• Informally known as tineas or ringworm

• Tinea capitis: scalp ringworm

• Tinea cruris: jock itch

• Tinea pedis: athlete’s foot

• Tinea unguium: ringworm of nails

Fungi involved in Cutaneous Mycoses

• Trichophyton

• Microsporum

• Epidermophyton

Treatment = topicals (miconazole & clotrimazole)

Subcutaneous Mycoses

• More serious than cutaneous mycoses; penetrate the stratum corneum

• Usually caused by fungi that inhabit the soil

Sporotrichosis (subcutaneous mycoses)

• Caused by Sporothrix schenkii; dimorphic fungus

• Enters a wound; forms a small ulcer

• Treated with potassium iodide

Candidiasis

• Overgrowth of Candida albicans (yeast)

  • Forms pseudohyphae, making it resistant to phagocytosis

• Occurs in the skin and mucous membranes of the genitourinary tract and mouth

  • Thrush: C. albicans infection of the oral cavity

• Results when antibiotics suppress competing bacteria or a change occurs in the mucosal pH

• Fulminating disease in the immunosuppressed

• Treatment → Miconazole & clotrimazole topically

Scabies

• Caused by Sarcoptes scabiei mites

  • Burrow in the skin to lay eggs

• Causes inflammatory skin lesions

• Transmitted via intimate contact

• Treatment with permethrin

Pediculosis (Lice)

• Pediculus humanus capitis (head louse)

• P. h. corporis (body louse)

• Feed on blood from the host

• Lay eggs (nits) on the hair and attach to the shafts

• Treatment with topical insecticides (permethrin or pyrethrin)

  • Malathion, lindane, or ivermectin are used in cases of resistance

Inflammation of the Eye Membranes: Conjunctivitis

• An inflammation of the conjunctiva

• Also called red eye or pinkeye

• Commonly caused by Haemophilus influenzae, which is a bacterium unassociated with influenza infections

  • Also caused by adenoviruses

• Can be caused by pseudomonads associated with unsanitary contact lenses

Ophthalmia Neonatorum

• Caused by Neisseria gonorrhoeae

• Large amount of pus forms; ulceration of corneas results

  • Untreated cases may lead to blindness.

• Transmitted to a newborn’s eyes during passage through the birth canal

• Prevented by treating a newborn’s eyes with antibiotics

Inclusion Conjunctivitis

• Caused by Chlamydia trachomatis

  • Bacterium that grows as an obligate intracellular parasite

• Transmitted to a newborn’s eyes during passage through the birth canal

• Spread also through swimming pool water

• Treated with tetracycline

Trachoma

• Caused by some serotypes of Chlamydia trachomatis

• Leading cause of blindness worldwide

• Transmitted via hand contact or flies

• Infection causes permanent scarring; scars abrade the cornea, leading to blindness

  • Secondary infections can also be a factor.

• Oral azithromycin is used in treatment.

Keratitus

• Inflammation of the cornea

• Bacterial (United States) → Contact lenses

• Fusarium and Aspergillus (Africa and Asia)

Herpetic keratitis

• Caused by herpes simplex virus 1 (HSV-1)

• Infects cornea and may cause blindness

• Treated with trifluridine

Acanthamoeba keratitis

• Ameba transmitted via water and soil

• Associated with unsanitary contact lenses

• Mild inflammation followed by severe pain

• Treatment with 2% chlorhexidine and propamidine isethionate eye drops or topical neomycin

• May require a corneal transplant

Strategies to reduce incidence of neglected tropical diseases:

• Preventive chemotherapy

• Innovative, intensified disease management

• Veterinary care

• Vector control

• Improved sanitation and hygiene services

Subacute sclerosing panencephalitis

Rare; Occurring 1 to 10 years after measles recovery

Congenital rubella syndrome

• Fetal damage, deafness, heart defects, mental retardation in 35% of cases

• 15% mortality within first year of life