Infection

Question 1

Give four viruses that infect the skin

Answer 1

Human papilloma virus (HPV)
Herpes simplex virus (HSV)
Herpes zoster virus (HZV)
Molluscum contagiosum

Question 2

Give three bacteria that infect the skin

Answer 2

Staphylococcus aureus
Streptococcus spp
Corynebacterium minutissimum

Question 3

Give three yeast/fungi that infect the skin

Answer 3

Candida albicans
Pityrosporum
True fungi

Question 4

Give an example of a parasite that affects the skin

Answer 4

Scabies

Question 5

Which organism is the most common cause of viral warts?

Answer 5

Human papilloma virus

Question 6

Describe the Koebner (isomorphic) phenomenon

Answer 6

Linear pattern of skin lesions occurs due to infection of a scratch or other trauma. Occurs most commonly in HPV viral warts and Molluscum contagiosum (MCV) infection, and often happens when the patient scratches themselves while itching (auto-innoculation).

Question 7

Describe the management of viral warts

Answer 7

Usually self-limiting so do not require intervention. There is no treatment to kill the virus; any treatment just helps the body’s immune system.
Genital warts may be treated with Imiquimod.

Question 8

Describe the clinical progression of herpes simplex virus

Answer 8

Primary exposure often from another person’s cold sore. Tracks up cutaneous nerves once has penetrated epidermis, stays in dorsal root ganglia for life. First clinical episode usually most severe – fever, lymphadenopathy… takes about three weeks to clear up spontaneously. Recurrent episodes become less frequent and less severe over time, and usually present as cold sores.

Question 9

What can trigger a recurrence of HSV infection?

Answer 9

spontaneous
trauma
menstruation
sunlight 
fever

Question 10

Which group of patients is most at risk of developing a disseminated herpes simplex virus infection?

Answer 10

Immunocompromised patients (do not need to be severely immunocompromised)

Question 11

How is herpes simplex virus treated?

Answer 11

Acyclovir

- topical, oral of IV depending on severity

Question 12

Which virus is responsible for chicken pox? what happens when the virus is reactivated after the initial exposure?

Answer 12

Herpes zoster virus

Shingles

Question 13

Where do HSV and HZV lie dormant?

Answer 13

Dorsal root ganglia

Question 14

How is herpes zoster virus treated?

Answer 14

Generally self-limiting but can cause severe disease and risk of eye complications if it affects the opthalmic nerve. If treatment is needed, use acyclovir - higher dose needed than for herpes simplex

Question 15

Describe the potential complications of shingles

Answer 15

Post-herpetic neuralgia

• burning pain that remains even after the lesions have disappeared (does not occur in HSV infection)
• residual scarring
• teratogenic and can easily pass through the placenta during active infection (but not during latent phase)

Question 16

Describe the appearance of lesions caused by molascum contagiosum (MCV)

Answer 16

Umbilicated (look like they have “belly buttons”)

Self-resolving - usually last 9-12 months

Question 17

Define “Impetigo”

Answer 17

superficial infection, area ma be slightly raised
Causes sores and blisters which often appear as golden crusty lesions around the lips and cheeks
Appearance varies depending on location
Highly contagious - particularly common in children

Question 18

How is impetigo treated?

Answer 18

Localised infection - treat with topical antibiotics

Widespread infection - treat with a combination of topical and oral antibiotics

Question 19

Define “furucle”. Which organism is the most common cause?

Answer 19

Also known as a boil
An abscess that occurs in the hair root
Usually painful
Usually caused by staph aureus

Question 20

Define “carbuncle”

Answer 20

lots of boils next to each other

Question 21

Define “ecthyma”. Which organisms most commonly cause this?

Answer 21

A deeper form of impetigo, but a smaller area than cellulitis.
Infection causes deep erosions which can develop into ulcers
Usually caused by staph or group A strep
Occasionally can be caused by Pseudomonas aeruginosa

Question 22

What is ecthyma gangrenosum? Which group(s) of patients does it most commonly affect?

Answer 22

Ecthyma caused by Pseudomonas aeruginosa
Characterised by haemorrhagic pustules which develop into necrotic ulcers. Generally only seen in immunocompromised or very unwell patients.

Question 23

Describe the treatment of ecthyma gangrenosum?

Answer 23

Topical antibiotics that cover both staph and strep

Severe and/or persistent infections should be treated with oral flucloxacillin as well as the topical antibiotics

Question 24

Define “cellulitis”. Which organism most commonly cause this?

Answer 24

Skin infection involving the full thickness of the dermis and the subcutaneous fat. Often very swollen and can sometimes lead to ulceration.
More commonly caused by strep than staph

Question 25

What is the most significant potential complication of cellulitis? How should it be treated?

Answer 25

Bacteraemia; can lead to sepsis and septic shock which can be fatal Treat with IV antibiotics

Question 26

Which yeast is associated with fungal skin infections? Where are these infections most likely to develop?

Answer 26

Candida albicans | In areas where the skin is warm and moist, e.g. nappy rash

Question 27

Describe the appearance of lesions caused by candida albicans (yeast) infection?

Answer 27

Satellite lesions | Occasionally can develop pustules

Question 28

How can you differentiate between a bacterial and fungal nail infection?

Answer 28

Loss of cuticle | - show that the inflammation is chronic which suggests candida rather than a bacterial infection

Question 29

How are candida infection treated?

Answer 29

Mild infections treated topically | More severe infections need an oral anticandidal agent e.g. fluconazole.

Question 30

What is Pityriasis versicolor? How should it be treated?

Answer 30

A commensal yeast organism but can develop into a rash as the yeast transforms into a fungus. Treat with ketoconazole shampoo. Leaves faint pale areas after active infection has disappeared which take a long time to return to normal colour – melanocytes get temporarily switched off so don’t produce pigment. Important to reassure patients that this is not active infection.

Question 31

What is the commonest site of primary infection with true yeast (Tinia)?

Answer 31

Between the toes, particularly the fourth and fifth | Can then spread to other areas - always check the toes for present of primary infection.

Question 32

Describe the appearance of lesions caused by Tinia infection

Answer 32

Advancing red scaly edge - fungus is "chased" by the immune system. Infection of the hair roots can cause lumpy, nodular lesions due to more severe inflammation. This can also cause hair loss

Question 33

How are Tinia infections treated?

Answer 33

Oral and topical terbinafine

Question 34

What is tinia incognito?

Answer 34

Topical steroids without treating the fungus caues a shiny red appearance due to loss of the flaky edge.

Question 35

How is scabies transmitted?

Answer 35

Human to human; infection cannot establish itself in other species. Requires close and prolonged (>1min) skin-to-skin contact.

Question 36

Describe the appearance of lesions caused by scabies mites

Answer 36

First lesions that appear are little papules where the mite has burrowed into the skin (called a burrow). After six weeks, patient becomes allergic to proteins in faeces of scabies mite – causes itching and widespread rash, known as excoriations. Infection that develops on top (eg because of scratching) can cause pustules, usually staph aureus.

Question 37

Which areas of skin are the most common sites of scabies burrows?

Answer 37

``` Peripheral sites (mainly hands and feet) as mites prefer areas that are cool. Sometimes mites burrow into the scrotum (this is also a cool area); here the burrows appear as itchy lumps or nodules rather than proper burrows. ```

Question 38

Describe the management of scabies infestation

Answer 38

Everyone in close contact with the patient should be treated simultaneously to avoid risk of reinfestation. Apply a topical parasiticidal treatment overnight, then repeat a weak later. Apply to all areas of the body except for hair-covered scalp. First line treatment is permethrin 5% dermal cream,. Second line treatment is malathion 0.5% aqueous liquid.