Download MBBS Dermatology PPT 23 Scabies Pediculosis Lecture Notes

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Definition

?Scabies - common parasitic infestation caused by the

`itch'-mite: Sarcoptes scabiei var. hominis

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?Sarcoptes scabiei var. canis (dogs); Notoedres cati

(cats)

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Epidemiology

? More than 300 mil ion cases yearly world wide

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? M:F = 1:1
? Common in al ages, al races & socio-economic

groups, urban > rural.

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? Throughout the year, more in winter

?Overcrowding
?Immuno-compromised
?Poor socio-economic conditions,

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?Institutionalized e.g., prisons, mental

retardation, old-age homes
The Itch-Mite

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? Obligate parasite of humans
? Fertilized female mite: Ovoid body, flattened

dorsoventrally, 300 microns (female), 200 microns

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(male)

?Crawls 2.5 mm/day

male: dies after fertilization

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female: lays 40-50 eggs in a lifespan of 4-6 weeks,

eggs (ova): mature after several moults

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Eggs larva nymph adults ? [about 10 days for

male and 14 day for female]

? Average parasite index: 12 (classical scabies) ?

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Transmission

? Skin to skin: predominantly.
? ? Fomites, clothing, furniture-rare

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? Sexual y transmitted infection (STI)
? Incubation period in new cases : 3-4 weeks
? Symptoms due to hypersensitivity to mite and

products

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? Re-infection- incubation period: symptoms occur

almost immediately ? as memory T cel s are present
Clinical features

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? Symptoms
- Itching- more / severe at night, with skin rash
- Family members usual y also have similar complaints
? Signs

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- Characteristic distribution along the so cal ed circle of

Hebra: Imaginary circle intersecting the main sites of

involvement--axil ae, elbow flexures, wrists & hands

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and genitocrural area


Clinical features

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- Papules, vesicles, papulovesicles, scratch marks
- Burrow- classical lesion of scabies- grey-brown line

up to 5 mm, seen on webs & genitalia with mite as a

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black dot at the end

- Burrow may be a dot, dotted line, curve or curved

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line
Clinical features

? Secondary skin lesions
- Excoriations

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- Eczematization
- Nodules
- Pustules
- Urticaria?

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Clinical types

? Classical Scabies: characteristic distribution of

lesions along the circle of Hebra

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? Genital Scabies: sexual y transmitted
? Incognito: topical / systemic steroids
? Infants: scalp, palms, soles
? Nodular (sensitization): scrotum, penis, elbows,

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axil ary folds

? Animal scabies
Clinical types

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? Crusted (Norwegian scabies):
Mental y retarded (e.g., Down's syndrome),

neurological impairment / paralysis, immuno-

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compromised / HIV infection / AIDS, leprosy

? Highly infectious
? Severe; itching may not manifest; hundreds to

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mil ions of mites may be present; scaling

Complications

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? Secondary infection
? Eczematization
? Glomerulonephritis
? Phimosis, Paraphimosis
? Urticaria

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? Erythroderma
? Drug reactions: irritation, eczematization
Investigations

? Scraping: from papule, burrow to demonstrate mite,

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egg,

? Dermatoscopy is useful for detecting burrows and

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visualizing their contents

? IgE- specific levels
? Newer: Polymerase chain reaction, Immunosorbent

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assays? not available widely

Treatment-principles

? Treat secondary complications first

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? Treat al household members
? Treat al inmates and caretakers in institution
? Treat fomites / clothes by water & detergents (hot

water not absolutely necessary)

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? Topical scabicides to be applied thoroughly behind

ears and from neck to toes; in infants: on scalp & face

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if involved

? Repeat application depending upon scabicides used
First-line therapies

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? Topical permethrin 5%
? MoA- Impairs function of voltage-gated sodium

channels in insects, leading to disruption of

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neurotransmission

? Applied for 8 to 14 hours (overnight)
? I application- one to two weeks later- the relative

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efficacy of one versus two applications of permethrin

not studied

? ADR- Generally well tolerated; skin irritation

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Oral ivermectin

? Advantage of ease of administration
? 200 mcg/kg single dose, repeated after two weeks

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? MoA- Act by interrupting glutamate & GABA-induced

neurotransmission causing paralysis & death

? Lacks ovicidal action

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? Better with eczematised patients, in crusted scabies
? CI- < 5 years (<15 kg body wt); >60 years
? Pregnancy cat. C
Crusted scabies

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? Topical 5% permethrin or topical 5% benzoyl

benzoate applied daily for seven days, then

twice weekly until cure

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AND
? Oral ivermectin (200 mcg/kg/dose) given on

days 1, 2, 8, 9 and 15

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[Severe infestations- two additional doses (given

on days 22 and 29)]

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Supportive treatment

? Antihistaminics
? Antibiotics: systemic, local
? Emol ients

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? Acaricidal soaps (permethrin)?
? Steroids: Topical (in eczematised / nodular scabies)
? Keratolytics in crusted scabies
Failure of treatment

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? Improper treatment (clothing, underneath the nails)

? Poor compliance

? House hold and/or institutional contacts not treated

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? Resistance to drugs (lindane etc.)

Causes of itching even after treatment

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Itching persists for few days even after successful

treatment
? Re-infection / relapse
? Eczematous reaction

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? Contact irritation sensitization to acaricidal drugs
? Scabeitic nodules
? Other skin problems
Pediculosis

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? Types:
- Pediculus capitis -head louse
- Pediculus humanus -body louse
- Pthirus pubis- pubic/crab louse

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? Morphology:
- Head louse & body louse morphology identical
(Thin & long)
- Crab louse (broad & short)

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Normal Habitat

? Pediculosis capitis:
Scalp hair of host
Children, Females>males

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? Pediculosis corporis:
Clothing close to skin of host
Vagabond's disease - pigmentation of the skin caused

by long continued exposure, uncleanliness, and

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especial y by scratch marks and other lesions due to

the presence of body lice
? Phthiriasis :

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? Pubic, axillary, beard hair, eyebrows; eyelashes; hair

of trunk & limbs; rarely scalp margins.

? Sexually active young adults; in children due to

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sexual abuse or parental contact.

Clinical features

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Pediculosis capitis:
? Scalp pruritus
? Detection of nits / adults lice on scalp hair
? Secondary bacterial infection
? Cervical lymphadenopathy

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? Matting of hair with pus and exudate - plica polonica
? Eczematization- neck /generalized
Clinical features

Pediculosis corporis:

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? Body pruritus
? Detection of nits / lice on clothing
? Secondary bacterial infection
? Postinflammatory hyperpigmentation of skin

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Phthiriasis:
? Nocturnal pruritus
? Detection of nits & louse on affected hair
? Blue grey macules (maculae caerulae) / Rust coloured

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speckles on skin

Pediculocides

Head lice: Topical treatment:

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Drug

Dose

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Remark

Permethrin

10

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lotion, 1%

minutes

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I application - day 9

Malathion 0.5% 8-10 hr /

lotion

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20

Repeat after 10 days

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minutes

Lindane 1%

4-5

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minutes 2 applications (9-10 days)

Ivermectin lotion,

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10

0.5%

minutes

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Wash after 24 hours
? Ivermectin 200-400 mcg/kg on day 1, 8 & 15
? Cotrimoxazole- kills the symbiotic bacteria in the gut

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of the louse or a direct toxic effect on the louse

Body louse

? Difficult

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? The most important treatment- disinfestation of all

clothing & bedding

? Beds should burned or sprayed with lice sprays-

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louse may lay eggs on the seams of the mattress etc.

? The patient should be treated from head to toe with

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a topical insecticide or given oral ivermectin
Pediculosis pubis

? Shaving- not curative as the louse will go to another

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hairy area of the body

? Crab lice are treated with the same topical therapy as

that for pediculosis capitis

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Pediculosis : Treatment

Pediculosis / Phthiriasis:
? Good hygiene

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? Treatment of patients & contacts.
? Removal of nits & lice with comb, vinegar,
application.
? Eyelash infection (phthriasis palpebrum):
Mechanical removal, Epilation, Topical agents

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