Microbiology: A Systems Approach, 2nd ed.

Chapter 18: Infectious Diseases Affecting the Skin and Eyes

Figure 18.1

Skin Defenses

• Keratinized surface• Constant sloughing off of cells from the

stratum corneum• Antimicrobial substances

– Sebum– Sweat– Antimicrobial peptides in epithelial cells

18.3 Normal Biota of the Skin

• Must be able to live in dry, salty conditions• Microbes grow in dense populations in moist

areas and skin folds or in hair follicles and glandular ducts

Three Main Categories• Diphtheroids

– Club-shaped– Gram positive– Not usually virulent– Propionibacterium acnes

• Microcci– Staphylococcus and Micrococcus– S. epidermis

• Yeasts – Low numbers, can cause opportunistic disease– Candida albicans– Malassezia

18.4 Skin Diseases Caused by Microorganisms

• Acne– All follicle-associated lesions– Skin prone to pimples and acne

• Structure that traps the mass of sebum and dead cells, clogging the pores

• Exaggerated process of keratinization in and around the follicle, blocking the pore

• Overproduction of sebum when the sebaceous gland is stimulated by hormones

– Propionibacterium acnes in the follicle releases lipases to digest the oil surplus, results in intense local inflammation that can eventually burst the follicle

Types of Lesions in Acne

• Comedo: skin initially swells over the pore leading out of a hair follicle– Pore closed- whitehead– Pore open but blocked with a dark plug of sebum-

blackhead• Pustule or papule: when the lesion erupts on

the surface• Cysts: pustules that come to involve deeper

layers of skin

Impetigo• Superficial bacterial infection• Causes the skin to flake or peel off • Highly contagious• Usually seen in children• Either Staphylococcus aureus or Streptococcus

pyogenes• Looks like peeling skin, crusty and flaky scabs, or

honey-colored crusts• Lesions usually found around mouth, face, and

extremities• Itches

Figure 18.2

Figure 18.4

Cellulitis

• Caused by a fast-spreading infection in the dermis and the subcutaneous tissues

• Causes pain, tenderness, swelling, and warmth

• Lymphangitis often occurs

Staphylococcal Scalded Skin Syndrome (SSSS)

• Dermolytic condition• Caused by Staphylococcus aureus• Mostly in newborns and babies• Can be thought of as a systemic form of

impetigo• Bullous lesions• Desquamation of the skin

Figure 18.7

Gas Gangrene

• Clostridial myonecrosis• Caused by Clostridium perfringens• Two forms

– Anaerobic cellulitis– True myonecrosis

Figure 18.8

Chickenpox• Generally a mild disease• In immunocompromised people, can be life

threatening• Fever and abundant rash that begins on scalp,

face, and trunk; radiates in sparse crops to the extremities (centripetal distribution)

• Lesions form macules and papules to itchy vesicles filled with a clear fluid

• In several days, encrust and drop off• Shingles: the virus enters the sensory endings

that innervate dermatomes and becomes latent- them reemerges

Figure 18.10a

Figure 18.11

Smallpox• Naturally occurring smallpox no longer occurs,

but may be a bioterrorism threat• Fever and malaise, then a rash in the pharynx• Spreads to the face and progresses to the

extremities• Initially a macular rash, then turns to popular,

vesicular, and pustular before crusting over• Two forms

– Variola minor– Variola major

• Highly virulent• Causes toxemia, shock, and intravascular coagulation

Figure 18.10b

Maculopapular Rash Diseases

• Measles• Rubella• Fifth disease• Roseola

Measles• Also known as rubeola• Sore throat, dry cough, headache, conjunctivitis,

lymphadenitis, and fever• Koplik’s spots appear then turn in to red

maculopaular exanthem• Erupts on the head then progresses to the trunk

and extremities until most of the body is covered• Complications can result

– Pneumonia– Laryngitis– Secondary bacterial infections– Subacute sclerosing panencephalitis (SSPE)

Figure 18.12

Rubella

• Also known as German measles• Relatively minor rash disease with few

complications• Two forms

– Postnatal infection– Congenital infection

• Teratogenic virus• Transmission of virus to a fetus in utero• Mother can transmit the virus even if she is asymptomatic• Fetal injury varies depending on the time of infections

Fifth Disease

• Erythema infectiosum• “slapped-cheek” appearance• Spreads on the body but is most prominent on

arms, legs, and trunk• Maculopapular, blotches run together• Low-grade fever and malaise

Roseola

• Common in young children and babies• Most cases proceed without the rash stage;

others result in maculopapular rash• High fever• Fourth day, fever disappears, and rash can

appear

Scarlet Fever

• Most often the result of a respiratory infection with Streptococcus pyogenes

Warts

• Also known as papillomas• Affect children more than adults• Benign squamous epithelial growths• Various types

– Seed warts– Genital warts– Plantar warts

Molluscum contagiosum

• Smooth waxy nodules on the face, trunk, and limbs

• May be indented in the middle• May contain milky fluid• Common in children• Most often causes nodules on the face, arms,

legs, and trunk in children; mostly in genital areas in adults

Large Pustular Skin Lesions

• Leishmaniasis• Cutaneous anthrax

Leishmaniasis

• Zoonosis transmitted by female sand flies• Several different forms, depending on the

species of Leishmania that is involved– Cutaneous leishmaniasis– Espundia– Systemic leishmaniasis

Cutaneous Anthrax

• Most common and least dangerous version of infection with Bacillus anthracis

• Caused by endospores entering the skin through small cuts or abrasions

• Papule that becomes increasingly necrotic then ruptures to form a black eschar

Ringworm (Cutaneous Mycoses)

• Dermatophytes• Confined to the nonliving epidermal tissues

and their derivatives• Different names all beginning with the word

tinea

Superficial Mycoses

• Involve the outer epidermal surface• Ordinarily innocuous infections with cosmetic

rather than inflammatory effects• Tinea versicolor caused by Malassezia furfur

18.7 Eye Diseases Caused by Microorganisms

• Conjunctivitis– Infection of the conjunctiva– Fairly common– Can be caused by specific microorganisms,

contaminants, or accidental inoculation of the eye– Inflammation and discharge

• Bacterial infections- milky discharge• Viral infections- clear exudate

Figure 18.21

Trachoma• Chronic Chlamydia trachomatis infection of the

epithelial cells of the eye• Major cause of blindness in certain parts of the

world• First signs of infection- mild conjunctival

discharge and slight inflammation of the conjunctiva

• Followed by marked infiltration of lymphocytes and macrophages

• As these cells build up, they impart a pebbled appearance to the inner aspect of the upper eyelid

• Eventually, pannus occurs

Figure 18.22

Keratitis

• More serious infection than conjunctivitis• Invasion of deeper eye tissues occurs, can lead

to complete corneal destruction• Any microorganism can cause this condition• One of the more common causes: herpes

simplex virus• Preliminary symptoms: gritty feeling in the

eye, conjunctivitis, sharp pain, and sensitivity to light

River Blindness

• Chronic parasitic (helminthic) infection• Onchocerca volvulus transmitted by black flies• The worms eventually invade the entire eye,

producing inflammation and permanent damage to the retina and optic nerve