Most common cause of skin infection

Yellow creamy pus-filled abscesses

Begins as folliculitis

MRSA - treat with vancomycin, lenzolid, quinopristin-dalfoprisin, daptomycin

MSSA - treat with nafcillin

Ritter's disease, Lyell's disease, toxic epidermal necrolysis

Large, clear fluid-filled blisters

Loss of overlying epidermal layer

exfoliatin or scalded skin syndrome toxin

Toxic Shock Syndrome (tampon use)

fever, hypotension, diffuse macular erythematous rash

Desquamation of skin, esp palms and soles

exotoxin TSST1 acts as superantigen

Tx: drainage, fluid replacement, antistaph chemo

Yellow, crusted lesions limited to the epidermis

caused by streptococcal pyogenes

Involves the dermal lymphatics

Caused by Streptococcus pyogenes

Areas of erythema and induration

Butterfly-wing rash on face

Group A streptococci

24-48 hr onset of inflammatory response

M surface protein inhibits opsonizaiton and confers resistance to phagocytosis

Spreads via hyaluronidase

lymph involvement

lysogenic strains - pyrogenic toxins (SPE) cause diffuse erythematous rash of scarlet fever

Streptococcus pyogenes skin infection

Deposition of immune complexes on glomerular basement membrane

M49 surface protein

Gram-positive cocci

Treated with penicillin or oral cephalosporin for allergic pts

Acute spreading infection of the skin involving the subcutaneous tissues

usually Strep. pyogenes or Staph. aureus

enlarged lymph nodes, malaise, chills, fever

Anaerobic cellulitis in areas of traumatized or devitalized tissue

frequently fatal mixed infection of anaerobes and facultative anaerobes

"flesh-eating"

streptococcus pyogenes

Gas gangrene

(Clostridial myonecrosis)

 Caused by Clostridium perfringens

Spores found in feces and contaminated soil

Commonly affects butt and perineum (anaerobic tissue)

In subcutaneous tissue, produce gas and anaerobic cellultis

In muscle, cause necrosis and gas bubbles

Lecithinase (alpha toxin); seen in Nagler reaction

plugs of keratin block the pilosebaceous duct (blackheads or comedones)

treat with tetracyclines or erythromycin

Mycobacterium leprae

Transmission by direct contact and aerosol inhalation

Grows in skin histiocytes, endothelial cells, Schwann cells of peripheral nerves

Very slow growth

Stain with Ziehl-Neelson or auramine shows acid fast rods and granulomas

blotchy red lesions

areas of local anesthesia

palpable thickening of peripheral nerves

vigorous CMI response

Sparse acid-fast rods in Ziehl-Neelsen/auramine stain

combo tx of dapsone and rifampin for 6 months

 extensive skin involvement

eventual lion-like facial appearance

progressive destruction of nasal septum

weak CMI response

Numerous acid-fast rods in Ziehl-Neelson/auramine stain

Triple therapy of dapsone, rifampin, clofazimine for at least 2 yrs

Assoc. with water or marine organisms

Trauma acquired while in swimming pool, cleaning aquarium 

Initally, lesions are small papules that enlarge, suppurate, and potentially ulcerate

Granulomas

"Buruli ulcers"

chronic, painless cutaneous ulcers

Africa and Australia origin

Pityriasis versicolor

(M. (Pityrosporum) furfur)

yeast

trunk, proximal limbs

hypo- or hyperpigmented macules that coalesce to form scaling plaques

round yeast forms seen in microscope

Tx with topical azole antifungal or selenium sulfide lotion

Anthrophilic species are most common

Zoophilic species: Trichophyton verrucosum (cattle), T. mentagrophytes (rodents), Microsporum canis (cats and dogs)

Geophilic species: Microsporum gypseum (gardners, agricultural workers)

**zoo and geo have greater inflammatory response

invade keratinocytes, spread by arthrospores

tinea capitis, corporis, cruris, manuum, unguium, pedis

annular or serpentine scaling patch with raised margin

itching; dry, scaly skin

fluoresce under UV light

Ectothrix infxn = outside of hair shaft; Microsporum

Endothrix infxn = majority; inside of hair shaft; Trichophyton 

Requires moisture for growth

Colonizes damaged skin and intertriginous areas

subcutaneous mycosis

Sporothrix schenkii - saphrophytic fungus widespread in nature (soil, rose and berberis bushes, tree bark, sphagnum moss)

farmers, gardeners, florists

small papule or subcutaneous nodule that eventually spreads and forms secondary nodules along lympatics

tx with potassium iodide or azole drugs

subcutaneous infection

Cladosporium and Phialophora

subcutanous fungal infection

Pseudallescheria and Madurella

causes Madura foot

endemic in Central and North America and Africa

skin lesions caused by blastomyces dermatididis

Acquired by spore aspiration and spreads from lungs

Bite of sandfly

Old World and New World parasite

ranges from localized self-healing ulcers to non-curing disseminated leprosy-like lesions

Mucocutaneous leishmaniases

Bite of sandfly

New World parasite

Localized in the skin or invades skin-mucous surfaces

Gives rise to chronic disfigurement

snail vector: gives rise to dermatitis

bird vector: more pronounced skin rxn; "swimmer's itch"

nematodes Ancylostoma and Necator

invasion causes dermatitis

migration of larvae parallel to skin causes intensely itchy sinuous inflammatory trails ("creeping eruption")

tx with thiabendazole (antihelmintic)

River blindness

Onchocerca volvulus

live in subcutaneous nodules

released microfilariae can invade the eye

begins as erythematous, papular, intensely itchy rashes

later, skin thickening, lost elasticity, excessive wrinkling, depigmentation

tx with ivermectin, but skin conditions are irreversible

dipterous flies, Dermatobia

Eggs are layed directly onto skin, causing painful reactions

infection head and body lice of Pediculus

encrusting inflammatory masses

tx with Malathion or carbaryl

Develops in damaged tissue from trauma or surgery

Caused by anaerobic bacteria or a mix of aerobic/anaerobic

Common in diabetics (particularly the feet)

Osteomyelitis is a common sequelae

Typically caused by microaerophilic streptococci and S. aureus

Most common following surgery of the groin or inguinal areas

black necrosis at center of cellulitis

HPV 6, 11, 16, 18

Infect anogenital tract and other mucosal areas

HPV 1 and 4

On soles or toes of the foot

icosahedral, dbl-stranded DNA

after infection, DNA remains in latent state in basal cell layer

Tx with karyolytic agents (salicylic acid, cryotherapy with dry ice or liquid nitrogen)

rare autosomal recessive disease

multiple warts with many different HPV types

immunologic defect

warts may change to squamous cell carcinomas

Caused by poxvirus

Unbilicated center

spread by contact

Contagious pustular dermatitis

papulovesicular lesions caused by poxvirus

acquire by contact with infected sheep or goats

transmitted via saliva or cold sores

virus replicates in mucosal cells, forming vesicles

vesicles ulcerate, become coated with whitish-gray slough

latent virus remains in the sensory ganglion for life

prodrome of pins/needles, pain, burning, itching

opthalmic branch of trigeminal ganglion = corneal ulcer

tx with acyclovir, valciclovir, famciclovir

infection of eczematous skin in young children

acute necrotizing encephalitis

neonatal infection from mother's genital tract

primary or reactivated HSV in immunocompromised pts

dbl-stranded DNA virus identical to HSV

virus grows more slowly than HSV

inhalation of droplets from resp. secretions or contact

Primary infection = chickenpox

Secondary infection = shingles

Dx by immunofluorescence using monoclonal Ab

Past infection indicated by IgGs seen in ELISA

Antiviral tx is offered, but not necessary

Caused by VZV

Crops of vesicles that develop in pustules and then scab

involves trunk, face, and scalp

multinucleated giant cells with intranuclear inclusions

complications are interstitial pneumonia and CNS involvement

maternal infection in first or second trimester

skin scarring, hypoplastic limbs, stigmata of eyes and brain 

Reactivation of latent VZV

thoracic dermatomes most commonly involved

may be pain and paresthesias

predispositions include increasing age, immunocompromise, or trauma/tumors affecting CNS

opthalmic involvement can threaten eyesight

postherpetic neuralgia is a common complication

Vesicular, mostly on buccal mucosa and tongue

when seen on hands and feet = "hand, foot, and mouth disease"; caused by coxsackievirus A16

Can also cause maculopapular rashes

maculopapular rashes 

often occur in summer

Slapped cheek syndrome - maculopapular rash on the face, fever

single-stranded DNA

require an adenovirus (helper virus) to replicate

 grows in hemopoietic cells in the bone marrow

causes roseola infantum (exanthem subitum)

common acute febrile ilness in infants and young children

characteristic maculopapular rash following fever

virus replicates in T and B cells and in the oropharynx

isolated from CD4+ T cells

virus persists in saliva

Kaposi's sarcoma skin lesions

common in parts of Mediterannean and Africa

Caused by a poxvirus

spread via contact with skin lesions and via respiratory tract

generalized vesiculopustular rash with later scarring

globally eradicated due to vaccinations

caused by paramyxovirus

incubation period of 9-10 days after infection (via respiratory droplets)

acute respiratory illness with runny nose, fever, cough, and potentially conjunctivitis

Koplik's spots appear on inside of cheek

maculopapular rash develops first on the face then spreads to the body and extremities

viral infection

transmitted by droplet infxn

causes a multisystem infxn with large impact on fetus

localizes to respiratory tract and skin, sometimes the placenta, joints, and kidney

fever, malaise, irregular maculopapular rash lasting 3 days

vaccine now exists

Causes Rocky Mountain spotted fever or typhus

invasion of vascular endothelial cells

acute vasculitis

pts, usually <4 yrs, develop fever, conjunctivitis, rash

dryness and redness of lips, red palms and soles with some edema, desquamation of fingertips

often arthralgia and myocarditis

likely caused by S. aureus/Strep. pyogenes superantigens

tx with high dose IV immunoglobulin

Myocarditis, pericarditis

viral myocarditis in infants

pleurodynia, epidemic myalgia (Bornholm disease)

chronic and severe muscle weakness for at least 6 mo, often as sequel to acute febrile illness

severe tiredness

depression, headache, anxiety

Typanosoma cruzi

carried by blood sucking bug

major sites of infection include CNS intestinal myenteric plexus, reticuloendothelial system, cardiac muscle

long term can cause heart failure

myocarditis, muscle fibrils and Purkinje fibers replaced by fibrous tissue

acute tx: nifurtimox, benznidazole; no longterm tx

from undercooked pork

sites of development include CNS and body muscles

cysts eventually become calcified

tx with praziquantel

invasion of striated muscle

infected pig meat

fever, muscle pains, weakness, eosinophilia

tx with mebendazole

protozoan acquired from infected meat

cause myositis

Hepatitis B = prodromal period, circulating immune complexes

Rubella = young women, following virus vaccine

Mumps = unusual, mostly men

Ross River, togaviruses = mosquite transmitted

Parvovirus = may follow adult infection

Campylobacter, Yersinia, salmonellae, shigellae, Chlamydia trachomatis (Reiter's syndrome)

immune-mediated, post-infectious arthritis

HLA-B27 associated

S. aureus = suppurative arthritis

Streptococci A and B

H. influenzae

Neisseria gonorrhoeae = multiple joints

Mycobacterium tuberculosis = bone lesions with weight bearing joints and bones

Borrelia burgdorferi = late feature of Lyme disease

Gram neg bacilli = neonates, elderly, immunocompromised

Sporothrix schenkii = fungal infection of joints

usually S. aureus

typically involves the growing end of a long bone

tends to occur in children and adolescents

HTLV-1

(human T-cell lymphotrophic virus type 1)

transmitted by maternal milk

(or sexual intercourse and IV drug users)

infects T cells; increased IL-2

5% develop T cell leukemia

mild febrile disease with lymphadenopathy

nodule and plaque formation in skin

increased susceptibility to opportunist infections

HTLV-2

(human T-cell lymphotrophic virus type 2)

IV drug users and Amerindian tribes in North, Central, and South America

causes myelopathy