Cutaneous parasitic infections (scabies, lice) Flashcards
Define scabies.
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
How common is scabies?
Usually affects children and young adults
What is the pathophysiology of scabies?
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
What are the risk factors for scabies?
- 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
What are the clinical features of scabies?
- 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
What is the management of scabies?
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
What is shown?
Crusted (Norwegian) scabies - seen in patients with suppressed immunity - especially HIV. Teeming with hundreds of thousands of organisms.
What is the management of Norwegian scabies?
Ivermectin
Isolation is essential
How do you diagnose scabies?
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
What are the complications of scabies?
- 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.
What is the diagnosis?
Scabies - A burrow on the palm - the mite can just be seen adjacent to the vesicle
Define pediculosis capitis.
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.
What is shown?
Pediculis humanus capitis - head louse
What are the risk factors for lice?
- 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
What are the clinical features of lice?
- 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.
How do you diagnose lice?
No tests required - clinical diagnosis
Fine toothed combing of wet or dry hair
What is the management of hair lice?
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.
What is the pathophysiology of head lice?
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.
What are the complications of lice? What is the prognosis?
- 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.
What is shown?
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.
