Cutaneous parasitic infections (scabies, lice)

Question 1

Define scabies.

Answer 1

Infestation with the ectoparasite Sarcoptes scabiei, a mite that burrows through the human stratum corneum.

Spread is primarily via direct contact with an individual with scabies

Question 2

How common is scabies?

Answer 2

Usually affects children and young adults

Question 3

What is the pathophysiology of scabies?

Answer 3

Burrows into skin, laying eggs in stratum corneum
Intense pruritus occurs due to delayed type 4 hypersensitivity reaction to mites/eggs which occurs about 30days after initial infection

Question 4

What are the risk factors for scabies?

Answer 4

• Overcrowded living conditions
• Contact with an infected person
• < 15yrs or > 65yrs
• Immunosuppression

NB: A brief handshake or hug does not usually allow for transmission unless the patient has crusted scabies

Question 5

What are the clinical features of scabies?

Answer 5

• Pruritus - widespread
• Linear burrows on sides of fingers, interdigitals webs and flexor aspects of wrist - NB: may affect face and scalp in infants
• Excoriation
• Nodules which may be skin coloured, red-brown, or violaceous
• Infection - secondary

Question 6

What is the management of scabies?

Answer 6

Conservative - avoid close contact until tx is complete; launder, iron or tumble dry clothing, bedding and towels on first day of treatment to kill mites

Medical -
* 1st line: Permethrin 5% - apply to all areas including face and scalp to cool, dry skin, creases and leave for 12-24hrs before washing off. Reapply if washed off. Repeat this treatment every 7 days.
* 2nd line: Malathion 0.5% - reapply

Question 7

What is shown?

Answer 7

Crusted (Norwegian) scabies - seen in patients with suppressed immunity - especially HIV. Teeming with hundreds of thousands of organisms.

Question 8

What is the management of Norwegian scabies?

Answer 8

Ivermectin
Isolation is essential

Question 9

How do you diagnose scabies?

Answer 9

Ectoparasite preparation under microscopy - presence of mite, eggs, or faecal material of mites

Other:
Skin biopsy - rarely shows the mites and faecal material
Epiluminescence light microscopy - presence of the mites indicated by small, dark, triangular structures located at one end of the linear burrow

Question 10

What are the complications of scabies?

Answer 10

• Post-scabetic pruritus
• Secondary infection
• Nodular scabies or pseudolymphoma

Prognosis: usually cured after 2 treatments of ivermectin or permethrin. But residual itching may remain for 1 month.

Question 11

What is the diagnosis?

Answer 11

Scabies - A burrow on the palm - the mite can just be seen adjacent to the vesicle

Question 12

Define pediculosis capitis.

Answer 12

AKA lice or nits

Head lice infestation with Pediculus humanus capitis, an obligate ectoparasite that lives on human beings and feeds on human blood.

Head lice infestation (pediculosis capitis) mainly affects those who are socially active, particularly young children.

Question 13

What is shown?

Answer 13

Pediculis humanus capitis - head louse

Question 14

What are the risk factors for lice?

Answer 14

• Age 3-12yrs
• Female (~3:1) - girls have longer hair, spend more time in closer play and have longer infestations.
• Close contact with an infested individual
• Overcrowding or close living conditions

Question 15

What are the clinical features of lice?

Answer 15

• Scalp pruritus
• Live nymphal or adult louse
• Eggs visible on hair shaft within 1cm of scalp

Other: small red papules on hairline from louse bites, occipital lymphadenopathy, erythema with honey-coloured crust.

Question 16

How do you diagnose lice?

Answer 16

No tests required - clinical diagnosis
Fine toothed combing of wet or dry hair

Question 17

What is the management of hair lice?

Answer 17

Conservative:
* NOT school exclusion
* Wet combing

Medical:
* Malathion
* Dimeticone or permethrin or ivermectin- a pediculicide
* Isopropyl myristate
* Cyclomethicone

NB: no need to treat household contacts unless they are found to have lice; only terat if living lice are found. School exclusion is not advised.

Question 18

What is the pathophysiology of head lice?

Answer 18

Head lice are small insects that live only on humans, they feed on our blood.

Eggs are grey or brown and about the size of a pinhead.

The eggs are glued to the hair, close to the scalp and hatch in 7 to 10 days.

Nits are the empty egg shells and are white and shiny. They are found further along the hair shaft as they grow out.

When newly infected, cases have no symptoms but itching and scratching on the scalp occurs 2 to 3 weeks after infection. There is no incubation period.

NB: They cannot jump, fly or swim.

Question 19

What are the complications of lice? What is the prognosis?

Answer 19

• Pruritus-associated sleep disturbance
• Impetigo - from secondary infection with staph or strep, reated with topical or oral antibiotics.

Prognosis - requires 2-4 cycles to kill all hatching nymphs. Empty egg cases will remain on the hair shafst for months if not removed.

Question 20

What is shown?

Answer 20

Pubic lice - spread by close contact and easily transmitted sexually. May spread to other parts of the body like axillae and eyelashes. Treated with insecticides like malathion/permethrin which is lathered and applied like shampoo.