Microbial Diseases Of The Skin & Eyes

Microbial Diseases of the Skin and Eyes

Skin

 The skin is generally inhospitable to the growth of certain microbes but supports the growth of some  Salt inhibits microbes  Lysozyme hydrolyzes peptidoglycan  Fatty acids inhibit some pathogens

Mucous Membranes    

Line body cavities Epithelial cells attached to an extracellular matrix Cells secrete mucus Some have cilia

Normal Microbiota of the Skin  Gram-positive, salt-tolerant bacteria Staphylococci Micrococci Diphtheroids  Vigorous washing reduce but does not eliminate the the normal microbiota - microorganisms in hair follicles & sweat glands reestablish normal population after washing.

 Increase number of microorganism in moist areas of the body ( Armpits )

Body Odor

Microbial Diseases of the Skin  Skin lesions & rashes does not necessarily indicate infections of the skin but maybe manifestations of systemic disease.  Exanthem Skin rash arising from another focus of infection  Enanthem Mucous membrane rash arising from another focus of infection

BACTERIAL DISEASES OF THE SKIN  Staphylococcus & Streptococcus 1. Come in contact with the skin & are adopted to the skin’s physiologic conditions 2. Produce invasive & damaging enzymes

Staphylococcal Skin Infections  Staphylococcus - spherical, Gram- positive - irregular grape-like clusters

 Types of Staph. 1. Coagulase-positive - produces Coagulase – an enzyme that clots fibrin. - fibrin clot protects the organism from phagocytosis 2. Coagulase- negative - does not produce Coagulase - 90% of skin normal flora - pathogenic only when skin barrier is broken ( Insertion & removal of catheter)

 Staphylococcus epidermidis - Gram-positive cocci, coagulase-negative - found in human skin - found in catheters surrounded by slime layer of capsular material - protection against dessication & disinfection

 Staphylococcus aureus - Gram-positive cocci, coagulase-positive - most pathogenic - forms golden yellow colonies

 Toxins produced by Staph. Aureus: 1. Leukocidin 2. Exfoliative toxin 3. Enterotoxin Problems in Staph. Infection: 1. Dangers to surgical wounds - S. aureus is carried by hosp. staff & visitors 2. Antibiotic resistance - only 10% are sensitive to Penicillin

3. Favorarable environment provided by nasal passages 4. Hair follicles as reservoirs

Staphylococcal Skin Infections: 1. Folliculitis - Infections of hair follicles

 Sty Folliculitis of an eyelash  Furuncle ( Boil ) Abscess; pus surrounded by inflamed tissue  Carbuncle Inflammation of tissue under the skin

 Impetigo of the newborn - Stap. Aureus - thin walled vesicles on the skin that rapture & crust

 Scalded skin syndrome - Stap. aureus toxin entering the bloodstream - newborn or children below 3yrs. Old - lesions develop into a bright red area then peels off

Streptococcal Skin Infections  Streptococcus - gram- positive, spherical, in-chains - causes a wide range of disease - produces & secretes toxins, enzymes & virulence factors

Toxins & Enzymes produced: 1. Streptokinase 2. Hyaluronidase 3. Deoxyribonucleases 4. Leukocidins 5. Erythrogenic toxins 6. Exotoxin A

Streptococcal Skin Infections 1. Erysipelas - Streptococcus pyogenes - starts as sore throat skin erupts into reddish patches with raised margins

2. Impetigo - seen in toddlers & adults - associated with Staph. Infection

3. Cellulitis - infection of the connective tissue with inflammation of the subcutaneous layer.

4. Myositis – infection of the muscles

5. Necrotizing fasciitis - Infection of the deeper layer of the subcutaneuos tissue and into the fascia

Infections by Pseudomonads  Pseudomonads

- Gram-negative, aerobic rod - Widespread in soil, water & soap - Resistant to most antibiotics & disinfectants Pseudomonas aeroginosa - opportunistic pathogen - produces Endotoxin P - implicated in most nosocomial infection - indwelling medical tubes & devices mops, vases & diluted disinfectants

Diseases caused by Pseudomonas: 1. Pseudomonas dermatitis - self-limiting rash (2wks), swimming pools & saunas - enters through the hair follicles 2. Otitis externa / Swimmers ear - infection of the external ear 3. Post-burn infections - Pyocyanin produces a blue-green pus Tx: Fluoroquinolones Silver sulfadiazine

Acne  Comedonal acne Occurs when sebum channels are blocked with shed cells  Inflammatory acne Propionibacterium acnes Gram-positive, anaerobic rod Treatment: Preventing sebum formation (isotretinoin) Antibiotics Benzoyl peroxide to loosen clogged follicles Visible (blue) light (kills P. acnes)  Nodular cystic acne Treatment: isotretinoin

VIRAL DISEASES OF THE SKIN Warts / Verruca - Papillomaviruses, benign skin growth - person to person contact, sexually Tx: Removal - Cold liquid nitrogen, Electrodessication Acid burning

Poxviruses Smallpox (Variola) - Smallpox virus (Orthopox virus) Variola major has 20% mortality Variola minor has <1% mortality - transmitted by respiratory route & infects internal organs - Eradicated - bioterrorism

Herpesviruses Chicken pox / Varicella zoster - Varicella-zoster virus/Human herpes virus 3 - mild childhood disease - low mortality rate, high if contracted later in life - Mortality is due to complications - Encephalitis & Pneumonia - Serious fetal damage in 2% cases if it occurs during pregnancy

 Respiratory route

localizes in skin after 2wks Infected skin is vesicular then fills with pus then raptures

Scab Heal  Starts in the trunk then spreads to the extremities  Virus may remain latent in dorsal root ganglia - Central nerve gangliion - persists as viral DNA ( antibodies cannot penetrate the CNS)

Shingles / Herpes zoster - Reactivation of latent HHV-3 releases viruses that move along peripheral nerves to skin. - latent Varicella-zoster virus located at the Dorsal root ganglion ( spine) Reactivated ( decades later ) - Stress Low resistance Virions produced by reactivated DNA move down peripheral nerves

Cutaneous Sensory Nerves of the skin ( SHINGLES) -Vesicles similar to chicken pox -Unilateral( follows the cutaneous nerves) - Waist, face, upper chest, back - Severe burning, stinging pain for months to years ( Post Herpetic Neuralgia) - Adults

Herpes simplex 1 and Herpes simplex 2  Human herpes virus 1 and HHV-2 - Oral/Respiratory & Skin contact - Cold sores or fever blisters (vesicles on lips) 1. HHV-1 - Subclinical, Infancy - Herpes gladiatorum (vesicles on skin) Herpes whitlow (vesicles on fingers) HHV-1 can remain latent in trigeminal nerve ganglia

2. HHV-2 - Genital herpes, Sexual contact - Herpes encephalitis (HHV-2 has up to a 70% fatality rate)

- HHV-2 can remain latent in sacral nerve ganglia TX: Acyclovir

Men

Women

Measles (Rubeola)       

Measles virus Transmitted by respiratory route Incubation period: 10-12 days Infectious even before symptoms occur Humans are the only known reservoirs Macular rash Koplik's spots - lesions in the oral cavity - tiny red patches with central white specks on the oral mucosa opposite the molars.

 Symptoms develop like common colds  Macular rash starts on the face then spreads to the trunk & extremities

 Prevented by vaccination MMR - given age 1 yr  Complications: 1. Middle ear infection 2. Pneumonia 3. Subacute sclerosing panencephalitis - males - 1-10 yrs. After recovery from measles

Rubella (German Measles) Rubella virus Respiratory route Incubation period: 2-3 wks Milder disease than Rubeola often goes undetected  Macular rash and fever  Congenital Rubella Syndrome - severe birth defect if during 1st trimester - Deafness, cataract, heart defect, mental retardation    

 A 1905 list of skin rashes included #1-measles, #2scarlet fever, #3-rubella, #4-Filatow-Dukes (mild scarlet fever), and #5Fifth Disease / Erythema Infectiosum - Human parvovirus B19 - mild flu-like symptoms - facial rash “ Slapped cheek” Roseola - Human herpesvirus 6 - high fever and rash, lasting for 1-2 days - recovery leads to immunity

FUNGAL DISEASES OF THE SKIN & NAILS

Cutaneous Mycoses  Dermatomycoses: Tineas or Ringworm Metabolize keratin Trichophyton infects hair, skin, nails Epidermophyton infects skin and nails Microsporum infects hair and skin  Treatment: Oral griseofulvin Topical miconazole

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  Topical treatment with miconazole or nystatin

Microbial Diseases of the Eye  Conjunctivitis (pinkeye) - Haemophilus influenzae - Various microbes - Associated with unsanitary contact lenses  Neonatal gonorrheal ophthalmia - Neisseria gonorrhoeae - Transmitted to newborn's eyes during passage through the birth canal - Prevented by treatment newborn's eyes with antibiotics / Silver nitrate

 Chlamydia trachomatis Inclusion conjunctivitis - Transmitted to newborn's eyes during passage through the birth canal - Spread through swimming pool water - Treated with tetracycline Trachoma - Greatest cause of blindness worldwide - Infection causes permanent scarring; scars abrade the cornea leading to blindness

 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