Skin Infections

Question 1

What is the epidemiology of organisms that commonly cause skin infections?

Answer 1

a. More common in hot humid poor countries than hot temperate rich countries
b. Australia = more malignancy
c. Dermatitis is most common skin reason to go see doctor

Question 2

Biology of Staph aureus

Answer 2

a. Gram +ve
b. Commensal in 30% humans
d. Produces toxins
i. Exfoliative toxin -> staphylococcal scalded skin syndrome
ii. TSS Toxin 1 -> toxic shock syndrome
iii. Enterotoxin -> food poisoning
iv. Panton valentine leucocidin virulence factor -> necrotising soft tissue infection
e. Can also cause bone, joint, lung infections and sepsis
f. Treated with antibiotics

Question 3

S.aureus clinicaly

Answer 3

i. Impetigo = epidermis
ii. Folliculitis
iii. Ecthyma = dermis
iv. Boils
v. Carbuncles = several hair follicle abscesses

Question 4

3. What is the biology of Treponema pallidum

Answer 4

a. Gram -ve spirochaete -> syphilis
b. Biology =
c. Can inc transmission of HIV

Question 5

Clinical treponema pallidum

Answer 5

d. 1st stage = painless ulcer at inoculation site (genital or oral)
e. 2nd = disseminated infection with generalised infection and lymphadenopathy
f. Latent = no clinical signs
g. Tertiary syphilis years later if no treatment = skin, neurological and vasc manifestations
h. Congenital = acquired perinatally across placenta
i. Early and late manifestations
ii. Usually secondary syphilis early
iii. Tertiary syphilis later
iv. Miscarriage, still birth, rashes, brain and neurological problems, bone disease
i. Clinical features
i. Rash on palms and soles

Question 6

Herpes biology

Answer 6

b. Type 2 = genital infections
c. Latency -> dormant state in neurones for type 1,2,3 (3 is chickenpox)
i. Will reactivate at same place
d. Transmission by direct contact

Question 7

Herpes clinical

Answer 7

e. Clinical
i. Vesicular rash (2 weeks)
ii. Eczema herpeticum
iii. Herpes encephalitis
f. Eczema is v susceptible
g. No vaccine but acyclovir

Question 8

Biology of varicella zoster

Answer 8

a. Also a herpes virus
b. Spread through inhalation or direct contact
c. Incubation = 12 days
d. Latent in dorsal horn sensory neurones

Question 9

Clinical varicella zoster

Answer 9

c. Incubation = 12 days
i. Fever, sore throat, malaise
ii. Next day = vesicular rash (less of face, even less on arms and legs, not on hands and feet)
e. Reactivate and cause herpes zoster (shingles)
i. Can be premeditated by pain
ii. Painful vesicular rash only along a dermatome
iii. Very bad if ophthalmic division of trigeminal involved bc eye consequences (affects the cornea)

Question 10

Tricophytum

Answer 10

a. Superficial fungal infections
b. Dermatophyte = type of fungus which infects parts of body which have keratin (skin, nails and hair)
c. Clinical infections have prefix of tinea then name of body part involved
i. May also be known as ringworm

Question 11

Clinical features tricophytum

Answer 11

d. Clinical
i. Erythematous scaly rash on skin or scalp
1) Scalp = tinea capitis if child only
2) If looks like s.aureus = Rare to have S.aureus on scalp of child but more common in adult
ii. Discoloured and crumbly nails

Question 12

Biology of scabies

Answer 12

a. Mite Sarcoptes Scabei burrows into skin

b. Exposure to mite faeces and eggs -> delayed allergic reaction

Question 13

Clinical features of scabies

Answer 13

i. Wide spread eczematous rash 4 weeks after original infestatoin
ii. Very itchy
c. Usu ally genital, nipples, wrists, finger webs, instep of feet, axillae
d. Secondary bacterial infection is common
e. Skin to skin contact