Microbial Diseases of the Skin and Eyes Chapter 21 Microbial Diseases of the Skin and Eyes

Structure and Function of the Skin Skin = epidermis (keratin) + dermis First line of defense (physical and chemical barrier) Unbroken epidermis is an effective physical barrier hair follicles, sweat gland ducts, and oil gland ducts provide passageways for microbes to enter the skin and penetrate deeper tissues Perspiration provides moisture and some nutrients for microbial growth; sebum provides some nutrients

Skin Perspiration contains salt and antimicrobial peptide to inhibit microbes Lysozyme hydrolyzes peptidoglycan Fatty acids (from sebum) inhibit some pathogen Figure 21.1

Mucous Membranes Line body cavities Epithelial cells attached to an extracellular matrix (basement membrane) Cells secrete mucus Some have cilia Often acidic; limit microbial population Lysozyme in tears destroys the cell wall

Normal Microbiota of the Skin Resistant to drying & tolerant to high salt Gram-positive, salt-tolerant bacteria Staphylococci Micrococci Diphtheroids Vigorous washing can reduce numbers, but will not eliminate them Figure 14.1a

Microbial Diseases of the Skin Figure 21.2

Microbial Diseases of the Skin Exanthem Skin rash arising from another focus of infection Enanthem Mucous membrane rash arising from another focus of infection Bacterial Disease of the Skin Staphylococcus & Streptococcus are frequent causes of skin-related diseases

Staphylococcal Skin Infections Staphylococci: gram-positive cocci in clusters S. epidermidis Gram-positive cocci, coagulase-negative very common on the skin (90% of the normal microbiota); opportunistic pathogen Staphylococcus aureus Gram-positive cocci, pathogenic S. aureus are coagulase-positive Leukocidin (destroy phagocytic leukocytes) Exfoliative toxin (cause scalded skin syndrome)

Staphylococcal Skin Infections Enterotoxin (cause Staphylococcal food poisoning) S. aureus in hospital environment quickly becomes resistant to antibiotics (MRSA) and vancomycin-resistant S. aureus Many S. aureus produce penicillinase Folliculitis Infections of hair follicles Sty Folliculitis of an eyelash

Staphylococcal Skin Infections Furuncle Abscess; pus surrounded by inflamed tissue Carbuncle Inflammation of tissue under the skin Impetigo of the newborn Toxemia Scalded skin syndrome Toxic shock syndrome (TSS) Figure 21.4

Streptococcal Skin Infections Gram-positive cocci in chains Secrete toxins and enzymes Hemolysins (toxin): lyse red blood cells Alpha-, beta-, gamma-hemolytic streptococci Beta-hemolytic streptococci often associated with human disease Further subdivided into different serological groups (A through T) Group A beta-hemolytic streptococci most important

Streptococcal Skin Infections Streptococcus pyogenes = group A beta-hemolytic streptococci M proteins Antiphagocytic Aid adherence for colonization of mucous membrane Figure 21.5

Streptococcal Skin Infections Generally localized Can be highly destructive; produce substances that promote the rapid spread of infection Streptokinases (dissolve blood clots) Hyaluronidase (dissolves hyaluronic acid that cement connective tissue) Deoxyribonucleases (degrade DNA) Erythrogenic toxins (cause red rash & other symptoms of scarlet fever)

Streptococcal Skin Infections Infects dermal layer of the skin Erysipelas Can progress to local tissue destruction Impetigo Isolated pustules that become crusted Toddlers and children of grade-school age Figure 21.6, 7

Invasive Group A Streptococcal Infections (“Flesh-eating bacteria”) Destroy tissue rapidly; mortality rates over 40% Streptokinases Hyaluronidase Exotoxin A (superantigen) Cellulitis Myositis Necrotizing fasciitis Figure 21.8

Infections by Pseudomonads Pseudomonas aeruginosa Gram-negative, aerobic rod Opportunistic pathogen; cause of many nosocomial infections Can grow on traces of unusual organic matter, soap films or cap liner adhesives; often grow in dense biofilms Resistant to many antibiotics and disinfectants Produce several exotoxins; also has endotoxin

Infections by Pseudomonads Pseudomonas dermatitis (swimming pool, hot tubs) Otitis externa (swimmer’s ear) Opportunistic pathogen Cystic fibrosis patients Post-burn infections pyocyanin produces a blue-green pus in burn patients

Acne Inflammatory acne Most common skin disease Caused by blockage of channels for the passage of sebum to the skin surface Three categories: comedonal acne, inflammatory acne, & nodular cystic acne Comedonal acne Occurs when sebum channels are blocked with shed cells Usually treated with topical agents that do not affect sebum formation Inflammatory acne Due to Propionibacterium acnes (Gram-positive, anaerobic rod)

Acne Nodular cystic acne Bacteria has a nutritional requirement for glycerol in sebum inflammation caused by free fatty acids formed from metabolizing the sebum formation of pustules and papules Treatment: Preventing sebum formation (isotretinoin teratogenic) Antibiotics Benzoyl peroxide to loosen clogged follicles Clear light system visible (blue) light (kills P. acnes) Nodular cystic acne Formation of nodules or cysts = inflamed lesions filled with pus deep within the skin leave prominent scars Treatment: isotretinoin

Viral Diseases of the Skin: Warts Benign skin growths caused by viruses Papillomaviruses different kinds of warts Do not form cancer; but papillomaviruses are associated with some skin & cervical cancer Transmitted through direct contact Treatment: Cryotherapy: apply extremely cold liquid nitrogen

Warts Electrodesiccation: dry them with an electrical current Burn them with acids Topical application of prescription drugs Imiquimod (stimulate interferon production) Interferon (injection) Lasers (risk of aerosol transmission)

Smallpox (Variola) Smallpox virus (Orthopox virus) Variola major has 20% mortality rate Variola minor has <1% mortality rate Transmission by respiratory route Eradicated due to successful vaccination & there are no animal host reservoirs for the disease Bioterrorism vaccination only for military and healthcare workers

Smallpox (Variola) Monkeypox outbreak (started in zoo monkeys) Known to jump from animals to humans; human-to-human transmission is very limited Seen some cases the USA recently Disease closely resembles smallpox in symptoms and mortality rate Prevention by smallpox vaccination

Chickenpox (Varicella) and shingles (Herpes Zoster) Chickenpox relatively mild in children; tends to be more serious in adults Results of initial infection with herpesvirus varicella-zoster (human herpesvirus 3) Transmitted via respiratory route & infection localized in skin cells Ability to remain latent within body cause shingles (a new outbreak of virus)

Chickenpox Causes pus-filled vesicles Virus may remain latent in dorsal root ganglia near the spine following a primary infection persists as viral DNA Escapes immune response (Ab cannot penetrate into the nerve cells & no surface viral Ags expressed) Figure 21.10a

Shingles Reactivation of latent HHV-3 releases viruses that move along peripheral nerves to skin. Triggered by stress, or lower immune competence due to aging Occur in distinctive areas (typically around waist); usually limited to one side of the body at a time Figure 21.10b

Herpes simplex virus (HSV) HSV-1 (Human herpes virus 1, HHV-1) and HSV-2 (HHV-2) HHV-1 transmitted by oral or respiratory routes Usually infected in infancy (subclinical infection) Cold sores or fever blisters (vesicles near the outer red margin of the lips) Remain latent in the trigeminal nerve ganglia Recurrence due to excessive exposure to UV radiation, emotional upsets, or hormonal changes

Herpes simplex Herpes gladiatorum (vesicles on skin) via skin contact among wrestlers Herpes whitlow (vesicles on fingers) among healthcare workers HHV-2 transmitted sexually (genital herpes) Can remain latent in sacral nerve ganglia Herpes encephalitis, rare, but can be caused by both viruses HHV-2 has up to a 70% fatality rate Acyclovir may lessen symptoms

Measles (Rubeola) Measles virus; humans are the only reservoir Transmitted by respiratory route; extremely contagious Infectious before symptoms appear Macular rash and Koplik's spots (lesions of oral cavity; diagnostic indicator) Prevented by vaccination Complications of measles: Encephalitis in 1 in 1000 cases Subacute sclerosing panencephalitis in 1/1,000,000

Measles (Rubeola) Figure 21.13

Rubella (German Measles) Rubella virus Transmitted via respiratory route Macular rash and fever Milder viral disease than rubeola (measles) Complications are rare (encephalitic in about 1/6,000, mainly in adults) Congenital rubella syndrome causes severe fetal damage during first trimester Prevented by vaccination

Other viral rashes Fifth disease Roseola A 1905 list of skin rashes included #1-measles, #2-scarlet fever, #3-rubella, #4-Filatow-Dukes (mild scarlet fever), and #5-Fifth Disease Human parvovirus B19 produces mild flu-like symptoms with facial rash (“slapped-cheek”) Roseola Human herpesvirus 6 causes a high fever and rash, lasting for 1-2 days Mild childhood disease

Fungal Diseases of the Skin and Nails Mycoses: any fungal infection of the body Cutaneous mycoses: fungal infection of the epidermis, nails, or hair Dermatophytes: fungi that colonize the hair, nails, and the outer layer of the epidermis Metabolize keratin Trichophyton: infects hair, skin, nails Epidermophyton: infects skin and nails Microsporum: infects hair and skin

Cutaneous mycoses Dermatomycoses (tineas or ringworm) Treatment Tinea capitis: ringworm of the scalp bald patches Tinea curis: ringworm of the groin, or jock itch Tinea pedis: ringworm of the feet, or athlete’s foot Tinea unguium (onychomycosis): nail infection Treatment Oral griseofulvin (for hair infection) Topical miconazole

Subcutaneous mycoses Subcutaneous mycoses: fungal infection of tissue beneath the skin Usually caused by fungi that inhabit the soil Sporotrichosis Sporothrix schenckii enters puncture wound form small ulcers on the hands Occurs among gardeners or others who work with soil Treated with ingestion of a dilute solution of potassium iodide (KI)

Candidiasis Candida albicans (yeast) Candidiasis may result from suppression of competing bacteria by antibiotics Occurs in skin; mucous membranes of genitourinary tract and mouth Thrush is an infection of mucous membranes of mouth If infection becomes systemic fulminating disease leading to death Topical treatment with miconazole or nystatin

Candidiasis Figure 21.17

Parasitic infections of the Skin: Scabies Tiny mite Sarcoptes scabiei burrows in the skin to lay eggs Figure 21.18

Scabies Intense local itching May appear as a variety of inflammatory skin lesions (due to secondary infections from scratching) Transmitted via intimate contact (sexually, too) Treatment with topical insecticides

Pediculosis (lice) Pediculosis: infestations by lice Pediculus humanus capitis (head louse) P. h. corporis (body louse) can spread diseases (epidemic typhus) Feed on blood Itching due to sensitization to louse saliva Scratching can lead to secondary infections Lay eggs (nits) on hair

Pediculosis (lice) Head louse has especially adapted legs to grasp scalp hairs Treatment with topical insecticides Combing out the nits with fine-toothed louse combs Figure 21.19

Microbial Diseases of the Eye Conjunctivitis (pinkeye): inflammation of the conjunctiva Haemophilus influenzae & adenoviruses Various microbes (bacteria, viruses, and protozoa) Associated with unsanitary contact lenses Neonatal gonorrheal ophthalmia Neisseria gonorrhoeae Transmitted to newborn's eyes during passage through the birth canal

Bacterial Diseases of the Eye Prevented by treatment newborn's eyes with antibiotics (silver nitrate in old days) Chlamydia trachomatis Inclusion conjunctivitis Transmitted to newborn's eyes during passage through the birth canal Spread through swimming pool water Treated with tetracycline ointment

Bacterial Diseases of the Eye Trachoma Greatest cause of blindness worldwide Infection causes permanent scarring; scars abrade the cornea leading to blindness Transmitted by hand contact or by sharing personal objects (e.g. towels) Treated with tetracycline ointments; control through sanitary practices and health education

Other Infectious Diseases of the Eye Keratitis: inflammation of the cornea Herpetic Keratitis Herpes simplex virus 1 (HHV-1) Infects cornea, may cause blindness Treated with trifluridine Acanthamoeba keratitis Transmitted from water Associated with unsanitary contact lenses Severe damage may require a corneal transplant

Microbial Diseases of the Eye Figure 21.21

Chapter Review 1. Review the structure and function of skin as the first line of defense Skin = epidermis (keratin) + dermis Unbroken epidermis is an effective physical barrier hair follicles, sweat gland ducts, and oil gland ducts provide passageways for microbes to enter the skin and penetrate deeper tissues Perspiration provides moisture and some nutrients for microbial growth; sebum provides some nutrients

Chapter Review Mucous membranes Perspiration contains salt and antimicrobial peptide to inhibit microbes Lysozyme hydrolyzes peptidoglycan Fatty acids (from sebum) inhibit some pathogen Mucous membranes Line body cavities Epithelial cells attached to an extracellular matrix (basement membrane) Cells secrete mucus Some have cilia

Chapter Review Normal microbiota of the skin Often acidic; limit microbial population Lysozyme in tears destroys the cell wall Normal microbiota of the skin Resistant to drying & tolerant to high salt Gram-positive, salt-tolerant bacteria (e.g. Staphylococci, Micrococci, Diphtheroids) Vigorous washing can reduce numbers, but will not eliminate them recolonize the skin

Chapter Review 2. Know the characteristics of bacterial pathogens that cause skin diseases & the infections they cause Staphylococcus & Streptococcus are frequent causes skin-related diseases Pseudomonads are opportunistic pathogens Staphylococcal skin infections Staphylococci: Gram-positive cocci in clusters Staphylococcus epidermidis (S. epidermidis) are coagulase-negative; 90% of the normal microbiota of the skin; opportunistic pathogen

Chapter Review Pathogenic S. aureus are coagulase-positive Produce leukocidin (destroy phagocytic leukocytes); exfoliative toxin (cause scalded skin syndrome); & enterotoxin (cause Staphylococcal food poisoning) Become antibiotic resistant quickly in hospital environment Diseases caused by S. aureus Folliculitis: infections of hair follicles Sty: folliculitis of an eyelash Carbuncle : inflammation of the tissue under the skin Impetigo of the newborn Toxemia

Chapter Review Streptococcal skin infections Scalded skin syndrome Toxic shock syndrome Streptococcal skin infections Streptococcus: gram-positive cocci in chains; classified into three groups based on their hemolytic ability Alpha-hemolytic: partial hemolysis of red blood cells (RBCs) Beta-hemolytic: complete hemolysis of RBCs Gamma-hemolytic: no hemolysis of RBCs Beta-hemolytic streptococci often associated with human disease; Group A most important

Chapter Review Group A beta-hemolytic streptococci = Streptococcus pyogenes (S. pyogenes) S. pyogenes’ pathogenicity due to M proteins (adherence & antiphagocytic) Streptokinases: dissolve blood clots Hyaluronidase: dissolve hyaluronic acid Deoxyribonucleases: degrade DNA Erythrogenic toxins: cause red rash & other symptoms of scarlet fever Diseases caused by S. pyogenes Erysipelas Impetigo

Chapter Review Invasive Group A Streptococcal infections Especially pathogenic; “flesh-eating bacteria” Destroy tissue rapidly; mortality rates over 40% Produce streptokinases, hyaluronidase, exotoxin A (major contributing factor by causing immune system to cause damage to the infected host) Diseases caused by invasive group A strep. Cellulitis Myositis Necrotizing fasciitis

Chapter Review 3. Know the viruses that cause skin diseases & the infections they cause Warts Papillomaviruses do not form cancer, but are associated with some skin & cervical cancer Chickenpox and Shingles Results from initial infection with herpresvirus varicella-zoster (human herpesvirus 3) Ability to remain latent in body, when reactivated later in life (a new outbreak of virus) cause shingles

Chapter Review Herpes simplex virus (HSV) Reactivation is triggered by stress, or lower immune competence due to aging Herpes simplex virus (HSV) HSV-1 (human herpes virus-1, HHV-1) cause cold sores or fever blisters (usually infected in infancy); herpes gladiatorum among wrestlers; herpes whitlow among healthcare workers Remain latent and reactivated due to excessive exposure to UV radiation, emotional upsets, or hormonal changes

Chapter Review Measles HSV-2 (HHV-2) cause genital herpes Can remain latent Both HHV-1 and HHV-2 can cause herpes encephalitic (rare) HHV-2 infection more fatal (70% fatality rate) Measles Measles virus (Rubeola) extremely contagious (infectious before symptoms appear) Prevented by vaccination

Chapter Review German measles (Rubella) Rubella virus; milder viral disease than measles Prevented by vaccination 4. Know some fungal diseases of the skin and nails Cutaneous mycoses: fungal infection of the epidermis, nails, or hair Caused by dermatophytes (fungi that colonize the hair, nails, and the outer layer of the epidermis); metabolize keratin

Chapter Review Trichophyton: infects hair, skin, nails Epidermophyton: infects skin and nails Microsporum: infects hair and skin Dermatomycoses (tineas or ringworm) Tinea capitis: ringworm of the scalp bald patches Tinea curis: ringworm of the groin, or jock itch Tinea pedis: ringworm of the feet, or athlete’s foot Tinea unguium (onychomycosis): nail infection Subcutaneous mycoses: fungal infection of tissue beneath the skin Usually caused by fungi that inhabit the soil

Chapter Review Sporotrichosis Candidiasis Sporothrix schenckii enters puncture wound form small ulcers on the hands Occurs among gardeners or others who work with soil Candidiasis Candida albicans (yeast) Candidiasis may result from suppression of competing bacteria by antibiotics Occurs in skin; mucous membranes of genitourinary tract and mouth

Chapter Review Thrush is an infection of mucous membranes of mouth If infection becomes systemic fulminating disease leading to death 5. Know the infectious diseases of the eye and the pathogens that cause them Conjunctivitis (pinkeye): inflammation of the conjunctiva Caused by various microbes (bacteria, viruses, and protozoa) Haemophilus influenzae & adenoviruses most common cause

Chapter Review Inclusion conjunctivitis Trachoma Caused by Chlamydia trachomatis Transmitted to newborn’s eyes during passage through the birth canal Spread through swimming pool water Trachoma Also caused by Chlamydia trachomatis Greatest cause of blindness worldwide; cause permanent scarring; scars abrade the cornea leading to blindness

Chapter Review Keratitis: inflammation of the cornea Herpetic keratitis Caused by herpes simplex virus 1 (HHV-1) Infects cornea, may cause blindness Acanthamoeba keratitis Caused by Acanthamoeba (protozoa) present in water Severe damage may require a corneal transplant