Skin infections

Question 1

Skin infections are more common where?

Answer 1

Hot humid conditions and poor populations

Question 2

Two important characteristics of staphylococcus aureus bacteria

Answer 2

gram positive
commensal
(= most common bacterial cause of skin infections)

Question 3

List the toxins produced by SA and the diseases/problems caused by each of this toxins

Answer 3

Panton Valentine Leuocidin => Necrotising soft tissue infections

Exfoliative toxin => Staphylococcal Scalded Skin Syndrome

TSST-1 (Toxic Shock Syndrome Toxin 1) => Toxic shock Syndrome

Enterotoxin => diarrhoea (food poisoning)

Question 4

State and describe the different manifestations of S. Aureus skin infections

Answer 4

Impetigo (and bullous/blistering impetigo) = infection of sub corneal layer of epidermis; looks like golden crusty skin

Folliculitis = infection mouth of hair follicle

Ecthyma = infection of full thickness of epidermis

Boil = abscess of hair follicle
Carbuncle = abscess of several adjacent hair follicles

Question 5

Treatment of SA infections?

Answer 5

Antibiotics

Question 6

What kind of bacterium is Treponema pallidum?

Answer 6

Gram negative spirochaete

Question 7

What disease is caused by Treponema pallidum?

Answer 7

Syphilis (=Sexually Transmited Disease)

Question 8

Describe the staging of syphilis

Answer 8

Primary (at 3-8 weeks):
- Painless ulcer (aka chancre) at inoculation site (Genital or oral)

Secondary (at 6-12 weeks):

• Disseminated infection
• Generalised maculopapular rash and lymphadenopathy
• Condyloma lata

Latent syphilis (no clinical signs)

Tertiary syphilis (usually years later):
- Skin, neurological and vascular manifestations e.g. bone lesions, gummatous lesions, thoracic aneurysm

Question 9

How is congenital syphilis acquired?

Answer 9

Acquired perinatally

Question 10

Human Herpes Viruses are what kind of viruses?

Answer 10

DNA viruses

Question 11

Type 1 and Type 2 HSV causes infections where? State the target cell?

Answer 11

Type 1 – causes oral infections.
Type 2 – causes genital infections.

Muco-epithelial cell

Question 12

HSV - Site of latency? State the significance.

Answer 12

Neuron

- there can be reactivation with reoccurrences of infection.

Question 13

How is HSV transmitted? List the clinical features.

Answer 13

Transmission by direct contact.

Clinical features:

• painful vesicular rash (heals over 2-4 weeks)
• eczema herpeticum
• herpes encephalitis

Question 14

State another name for Human Herpes Virus-3

Answer 14

Varicella Zoster Virus

Question 15

What deceases does VZV cause?

Answer 15

Chicken pox (primary infection)
Shingles

Question 16

Describe the pathogenesis of chicken pox

Answer 16

Prodrome of fever and malaise followed by development of widespread vesicular rash. Usually lasts ~2 weeks and then becomes latent. Can reactivate in shingles.

Question 17

What appears on the skin in the reactivation of the VZV infection as shingles? When might there be serious consequences?

Answer 17

Herpes Zoster or Shingles where there is reactivation of the VZV and a painful vesicular rash appears along the course of a dermatome.

There can be serious eye consequences if the distribution of the Ophthalmic Division of the Trigeminal nerve is involved.

Question 18

Trichophytum:

• Most common cause of what kind of fungal infection?
• What type of fungi is it?
• Particularly infects what?
• Describe the method of naming of clinical infections?

Answer 18

• This is a common cause of superficial fungal infections.
• It is a dermatophyte.
• Particularly infects parts of the body which have keratin, ie skin, nails and hair.

The names of clinical infections have the prefix ‘tinea’ then the Latin body part involved, eg tinea capitis, tinea manuum etc.

Question 19

Give an example of a common species of trichophytum.
What are the clinical manifestations of an infection from this species?
Treatment?

Answer 19

Trichophytum rubrum

The clinical manifestations:

• erythematous scaly rash on skin/scalp
• discoloured and crumbly nails.

These infections can be treated with topical or systemic antifungal medication such as Terbinafinew

Question 20

What is Scabies?

Answer 20

This is a skin infestation with the mite Sarcoptes Scabei.

Question 21

What does the mite do?

Answer 21

The mite burrows in the surface of the skin.

Question 22

Exposure to mite faeces and eggs causes what?

Answer 22

Exposure to mite faeces and eggs causes a delayed allergic reaction which results in a wide spread itchy eczematous rash

Question 23

Scabetic burrows can be found where on the body?

Answer 23

Burrows can be found in certain regions of the body e.g. genital region, nipples, wrists, finger webs, instep of the feet, axillae.

Question 24

What is common as a secondary manifestation of the scabetic burrows?

Answer 24

Secondary bacterial infection is common.

Question 25

Transmission and treatment of scabies?

Answer 25

Transmission is by skin to skin contact. Treatment is with topical of systemic insecticides.​