Transcript Microbiology: A Systems Approach, 2nd ed. Chapter 18: Infectious Diseases Affecting the Skin and Eyes.

Microbiology: A Systems
Approach, 2nd ed.
Chapter 18: Infectious Diseases
Affecting the Skin and Eyes
18.1 The Skin and Eyes
• The skin makes contact directly with the
environment
• Many infectious diseases include skin
eruptions or lesions as part of the course of
illness
• The eye surface is also exposed constantly to
the environment
18.2 The Skin and Its Defenses
• Integument: skin, hair, nails, sweat and oil
glands
• Several layers thick
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
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–
–
–
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 sebumblackhead
• Pustule or papule: when the lesion erupts on
the surface
• Cysts: pustules that come to involve deeper
layers of skin
Impetigo
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•
•
•
•
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
Impetigo Caused by Staphylococcus
aureus
• Coagulase test: any isolate that coagulates
plasma is S. aureus
• Confirmation using latex bead agglutination
test (binds to IgG antibodies)
Figure 18.3
Figure 18.4
Figure 18.5
Impetigo Caused by Streptococcus
pyogenes
• Activates plasmin, turning itself into a tissue
degrader
Figure 18.6
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)
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•
•
•
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
Figure 18.9
Vesicular or Pustular Rash Diseases
• Lesions called pox
• Chickenpox
• Smallpox
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 latentthem 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
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•
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•
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
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•
•
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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
Figure 18.13
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
Wartlike Eruptions
• Caused by viruses
• Most caused by one of more than 80 human
papillomaviruses (HPVs)
Warts
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•
•
•
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
Tinea Capitis: Ringworm of the Scalp
• Common in children
• Small scaly patches to a severe inflammatory
reaction to destruction of the hair follicle and
temporary or permanent hair loss
Figure 18.14
Tinea Barbae: Ringworm of the Beard
• Aka barber’s itch
• Chin and beard of adult males
Tinea Corporis: Ringworm of he Body
• Prevalent infection of humans
• Can appear nearly anywhere on the body’s
glabrous skin
• Usually appears as one or more scaly reddish
rings on the trunk, hip, arm, neck, or face
Figure 18.15
Tinea Cruris: Ringworm of the Groin
• Also known as jock itch
• Thrives under conditions of moisture and
humidity caused by sweating
Tinea pedis: Ringworm of the Foot
• Also known as athlete’s foot and jungle rot
• Connected to wearing shoes- keep feet in a
closed, warm, moist environment
Figure 18.16a
Tinea Manuum: Ringworm of the
Hand
• Almost always associated with concurrent
infection of the foot
• Usually occur on the fingers and palms of one
hand
Tinea Unguium: Ringworm of the Nail
• Superficial white patches in the nail bed, or
thickening, distortion, and darkening of the
nail
• Artificial fingernails can provide a portal of
entry into the nail bed
Figure 18.16b
Figure 18.17
Superficial Mycoses
• Involve the outer epidermal surface
• Ordinarily innocuous infections with cosmetic
rather than inflammatory effects
• Tinea versicolor caused by Malassezia furfur
Figure 18.18
18.5 The Surface of the Eye and Its
Defenses
• Exposed surfaces: conjunctiva and cornea
– Conjunctiva: thin membranelike tissue that covers
the eye (except for the cornea) and line the
eyelids
– Cornea: the dome-shaped central portion of the
eye lying over the iris
Figure 18.19
Defenses
• Film of tears
• Immune privilege
Figure 18.20
18.7 Normal Biota of the Eye
• Sparse
• Those bacteria that are found in the eye
resemble the normal biota of the skin
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
Figure 18.23