Chapter 21 - Microbial Diseases of the Skin and Eyes

Epidermis

Outer layer of skin composed of keratinized stratified squamous epithelium

Keratin

A fiber protein that is the principal component of hair, skin, and nails; waterproofing protein coating outer layer of epidermis

Dermis

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

Perspiration

The moisture given off through the pores of the skin; contains salt that inhibits microbial growth

Lysozyme

An enzyme found in saliva and sweat and tears that destroys the cell walls of certain bacteria

Antimicrobial peptides

Small peptides produced by epithelial cells that disrupt pathogen plasma membranes

Sebum

Oily substance secreted by sebaceous glands; fatty acids inhibit pathogen growth

Mucous membrane

An epithelial tissue that secretes mucus and that lines many body cavities and tubular organs including the gut and respiratory passages; some cells have cilia; often acidic

Normal microbiota of the skin

Gram-positive, salt-tolerant bacteria

Staphylococci

Micrococci

Diphtheroids (Proprionibacterium, Corynebacterium)

Yeast

Higher populations in areas that produce more sweat (eg armpits)

Vesicles

small, fluid-filled lesions

Bullae

Large blisters/vesicles larger than 1 cm in diameter

Macules

Flat spots on the skin, such as freckles; can be reddened lesions associated with infection

Papules

Firm raised areas on the skin

Pustules

Variously sized circumscribed elevations containing pus

Purulent

producing or containing pus

Exanthem

skin rash arising from a disease

Enanthem

mucous membrane rash arising from another focus of the infection

Staphylococci

Spherical shaped bacteria that form grape-like clusters

Coagulase

A bacterial enzyme that causes blood plasma to clot

Staphylococcus epidermidis

Component of normal skin flora. Contaminates blood cultures, prosthetic devices, and catheters; HAI/nosocomial infections; coagulase-negative

Staphylococcus aureus

Normal microbiota of skin and nasal passageways; forms golden-yellow colonies; coagulase-positive; may produce damaging toxins and cause sepsis

Avoids host defenses in the skin and secretes proteins and toxins that kill phagocytic cells

MRSA

Antibiotic resistant strain: methicillin-resistant staphylococcus aureus

Folliculitis

inflammation of the hair follicles

Sty

infection of an oil gland of the eyelid

Furuncle

boil; a painful, purulent nodule formed in the skin by inflammation originating in a hair follicle; caused by staphylococcosis

Carbuncle

skin infection composed of a cluster of furuncles spreading to subcutaneous tissue caused by staphylococcal bacteria

Impetigo

Bacterial skin infection characterized by isolated pustules that become crusted and rupture; spread by autoinoculation; caused by staphylococci

Scalded skin syndrome

Infection caused by staphylococci consisting of large, soft, vesicles over the whole body; Toxin B (exfoliative toxin) causes exfoliation of skin

Pemphigus neonatorum

impetigo of the newborn

Toxic shock syndrome (TSS)

a severe illness characterized by high fever, rash, vomiting, diarrhea, and myalgia, followed by hypotension and, in severe cases, shock and death; caused by Staphylococcus aureus TSST-1 toxin and Streptococcus pyogenes

Streptococci

Gram-positive cocci that occur in chains; produce hemolysins; beta-hemolytic species often cause disease

Lancefield groups

Streptococci species grouped alphabetically by serological similarities based on antigenic cell wall carbohydrates

Group A streptococci (GAS)

-also known as Streptococcus pyogenes

-eighty immunological types

-produce virulence factors

Streptolysins

Hemolysins produced by streptococci

M proteins

Streptococci virulence factors external to the cell wall; allow adherence and immune system avoidance

Hyaluronidase

Hydrolyzes hyaluronic acid found in connective tissue

Streptokinase

Streptococcal virulence factor that dissolves blood clots

Erysipelas

Acontagious disease of the skin and subcutaneous tissues caused by infection with streptococci organisms; redness and swelling of affected areas that can lead to sepsis

Necrotizing fasciitis

A severe infection caused by Group A strep bacteria which is also known as flesh-eating disease; exotoxin A acts as superantigen

Pseudomonas aeruginosa

Gram-negative, aerobic rod; produces pyocyanin (causes a blue-green pus), exotoxins and endotoxin; can grow in biofilms on medical devices, implants, and catheters; resistant to many antibiotics

Pseudomonas dermatitis

Self-limiting rash acquired in swimming pools

Otitis externa

Inflammation of the outer ear; "swimmer's ear"; caused by P. aeruginosa

Pseudomonas infections in burn wounds

Opportunistic infection; Pyocyanin pigment produces a blue-green pus; produce a grape-like, fruity odor

Buruli ulcer

Caused by Mycobacterium ulcerans and its mycolactone toxin.

Deep, damaging ulcers that can require amputation

Acne

Chronic papular and pustular eruption of the skin with increased production of sebum; most common skin disease in humans; caused by blockage of hair follicles; affected by hormones that increase sebum production

Comedonal (mild) acne

Occurs when sebum channels are blocked with shed cells; easily treated with topical formations

Inflammatory (moderate) acne

Caused by Propionibacterium acnes; metabolizes sebum and fatty acids produce an inflammatory response; treated with antibiotics and benzoyl peroxide

Nodular cystic (severe) acne

Inflamed lesions with pus deep in skin; leaves scars

Viral diseases of the skin

Many are transmitted via respiratory routes and are systemic

Many cause problems in children and developing fetuses

Warts

Growths on your skin caused by an infection with human papilloma virus, or HPV; treated with cryotherapy, electrodessication, or salicylic acid

Papillomavirus

Virus that causes warts and is associated with skin and cervical cancer; more than 50 types have been identified

Smallpox (Variola)

Caused by orthropoxvirus; Variola major (20-60% mortality) and Variola minor (<1% mortality); transmitted via respiratory route, moves into the bloodstream, and infects the skin within 10 days; no animal host reservoir allowed it to be completely eradicated from the human population; first vaccine ever made was for this using cowpox

Monkeypox

Virus related to smallpox affecting monkeys, other primates, and rodents; can jump to humans; endemic to Africa; prevented by smallpox vaccination

Chickenpox (Varicella)

Herpesvirus varicella-zoster (human herpesvirus 3)

Transmitted via the respiratory route

Causes pus-filled vesicles

Reye's syndrome

Severe complication of chickenpox; vomiting and brain dysfunction; aspirin increases risk

Breakthrough varicella

Varicella in previously vaccinated persons due to live attenuated vaccine; much milder than varicella in unvaccinated individuals

Shingles (herpes zoster)

Painful, blistering skin rash due to the varicella-zoster virus, the virus that causes chickenpox; the virus remains inactive (becomes dormant) in central nerve ganglia; reactivated virus follows peripheral cutaneous nerves causing neuralgia; prevented by zoster vaccine and treated with antiviral drugs

Herpex simplex

Caused by human herpesvirus 1 and 2 (HSV-1 and HSV-2); transmission via oral/respiratory route for HSV-1 and skin or sexual contact for HSV-2; vesicular lesions or ulcerative lesions of oral surfaces (cold sores/fever blisters)

Latent HSV-1

Virus remains dormant in trigeminal nerve ganglia; can be reactivated by sun, stress, or hormonal changes

Latent HSV-2

Virus remains dormant in sacral nerve ganglia near spine

Herpes gladiatorum

A skin infection caused by the herpes simplex type 1 virus causing vesicles on the skin

Herpes whitlow

Herpes simplex infection causing vesicles on the fingers, especially at the base of the fingernails

Herpes encephalitis

Herpes brain infection; treated with acyclovir

Measles (Rubeola)

Transmitted by respiratory route; cold-link symptoms, macular rash, Koplik's spots

Prevented by vaccination (MMR vaccine) for children over the age of 1; can cause encephalitis in rare cases

Subacute sclerosing panencephalitis

Caused by variant of measles virus. Occurs in children and young adults who had measles after a 6- to 10-year asymptomatic period. Causes progressive dementia, seizures, and paralysis, leading to death.

Rubella

A viral infection transmitted via the respiratory route characterized by a low-grade fever, and a fine, pink macular rash; also called German measles; prevented by MMR vaccine (not for pregnant women)

Congenital rubella syndrome

Rubella virus passed from mother to fetus; causes damage to fetus, deafness, heart defects, mental retardation, 15% mortality within first year of life

Fifth disease (erythema infectiosum)

A childhood disease caused by the human parvovirus B19. Mild flulike symptoms and red cheeks that appear to be "slapped" or "slapped cheeks" with facial rash

Roseola

Caused by human herpesvirus 6 (HHV-6) and 7 (HHV-7)

High fever and rash lasting for 1-2 days

Hand-foot-mouth disease

Enteroviruses

Spread via mucous or saliva (usually children)

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

Mycosis

fungal infection

Cutaneous mycoses

fungal infections affecting hair, skin, nails; caused by Trichophyton, Microsporum, and Epidermophyton; treatment with topical drugs (miconazole and clotrimazole)

Dermatomycoses (tineas)

occur on the head, groin, feet, or nails

fungus metabolizes keratin in epidermis

usually treated with topical antifungal drugs or griseofulvin (oral)

Tinea capitis

ringworm of the scalp

Tinea curis

jock itch. dermatophyte infection in groin

Tinea pedis

fungal infection of the foot; athlete's foot

Tinea unguium

fungal infection of the nails

Subcutaneous mycoses

More serious; fungal infections beneath the skin; usually caused by fungi found in soil

Sporotrichosis

Caused by Sporothrix schenkii; dimorphic fungus

Enters a wound; forms a small ulcer

Treated with potassium iodide

Candidiasis

Caused by opportunistic infection of Candida albicans associated with antibiotic use and pH changes; forms pseudohyphae and is resistant to phagocytosis; common in skin and mucous membranes; raised rash; treatment with miconazole

Thrush

C. albicans infection of the oral cavity

Fulminating Candidiasis

Rapid, sudden and severe candidiasis in immunosuppressed individuals; usually fatal.

Scabies

Contagious skin disease transmitted by the itch mite Sarcoptes scabiei, commonly through sexual contact; causes inflammatory skin lesions; treated with permethrin

Pediculosis

Infestation with lice that causes itching and dermatitis; lice feed on blood from host and lay eggs (nits) on the hair; treated with topical insecticides permethrin and pyrethrin; malathion, lindane and ivermectin used in cases of resistance

Pediculus humanus capitis

human head louse

Pediculus humanus corporis

human body louse

Conjuctivitis

Inflammation of the conjunctiva (pink eye) caused by Haemophilus influenze or adenoviruses; can be caused by pseudomonads associated with unhygienic use of contact lenses

Ophthalmia neonatorum

A purulent inflammation of the conjunctiva and/or cornea in the newborn caused by Neisseria gonorrhoeae; can lead to corneal ulceration and blindness if untreated; transmitted during passage through birth canal and prevented by treatment with antibiotics

Inclusion conjunctivitis

Caused by Chlamydia trachomatis; transmitted to a newborn's eyes during passage through birth canal; can also be spread through swimming pool water; treated with tetracycline

Trachoma

Chronic, contagious form of conjunctivitis caused by Chlamydia trachoma that is the leading cause of blindness worldwide; transmitted via contact or flies; can cause permanent scarring to cornea leading to blindness and secondary infections; treatment with oral azithromycin

Keratitis

Inflammation of the cornea of the eye caused mainly by bacteria in the US and by Fusarium and Aspergillus in other parts of the world

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 propamidine isethionate and neomycin

May require a corneal transplant

Neglected Tropical Diseases (NTDs)

infectious diseases that primarily affect the poorest regions of the world (many of which are located in the tropics) and have not been a priority for funding agencies, pharmaceutical companies, or global policymakers.