Download MBBS Dermatology PPT 23 Scabies Pediculosis Lecture Notes

Download MBBS (Bachelor of Medicine, Bachelor of Surgery) Dermatology PPT 23 Scabies Pediculosis Lecture Notes

Cutaneous Infestations:

Scabies, Pediculosis


?Scabies - common parasitic infestation caused by the

`itch'-mite: Sarcoptes scabiei var. hominis

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



? More than 300 mil ion cases yearly world wide

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

groups, urban > rural.

? Throughout the year, more in winter

?Poor socio-economic conditions,
?Institutionalized e.g., prisons, mental

retardation, old-age homes
The Itch-Mite

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

dorsoventrally, 300 microns (female), 200 microns


?Crawls 2.5 mm/day

male: dies after fertilization

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

eggs (ova): mature after several moults

Eggs larva nymph adults ? [about 10 days for

male and 14 day for female]

? Average parasite index: 12 (classical scabies) ??


? Skin to skin: predominantly.
? ? Fomites, clothing, furniture-rare
? Sexual y transmitted infection (STI)
? Incubation period in new cases : 3-4 weeks
? Symptoms due to hypersensitivity to mite and


? Re-infection- incubation period: symptoms occur

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

? Symptoms
- Itching- more / severe at night, with skin rash
- Family members usual y also have similar complaints
? Signs
- Characteristic distribution along the so cal ed circle of

Hebra: Imaginary circle intersecting the main sites of

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

and genitocrural area

Clinical features

- 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

black dot at the end

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

Clinical features

? Secondary skin lesions
- Excoriations
- Eczematization
- Nodules
- Pustules
- Urticaria?

Clinical types

? Classical Scabies: characteristic distribution of

lesions along the circle of Hebra

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

axil ary folds

? Animal scabies
Clinical types

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

neurological impairment / paralysis, immuno-

compromised / HIV infection / AIDS, leprosy

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

mil ions of mites may be present; scaling


? Secondary infection
? Eczematization
? Glomerulonephritis
? Phimosis, Paraphimosis
? Urticaria
? Erythroderma
? Drug reactions: irritation, eczematization

? Scraping: from papule, burrow to demonstrate mite,


? Dermatoscopy is useful for detecting burrows and

visualizing their contents

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

assays? not available widely


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

water not absolutely necessary)

? Topical scabicides to be applied thoroughly behind

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

if involved

? Repeat application depending upon scabicides used
First-line therapies

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

channels in insects, leading to disruption of


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

efficacy of one versus two applications of permethrin

not studied

? ADR- Generally well tolerated; skin irritation

Oral ivermectin

? Advantage of ease of administration
? 200 mcg/kg single dose, repeated after two weeks
? MoA- Act by interrupting glutamate & GABA-induced

neurotransmission causing paralysis & death

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

? Topical 5% permethrin or topical 5% benzoyl

benzoate applied daily for seven days, then

twice weekly until cure

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

days 1, 2, 8, 9 and 15

[Severe infestations- two additional doses (given

on days 22 and 29)]

Supportive treatment

? Antihistaminics
? Antibiotics: systemic, local
? Emol ients
? Acaricidal soaps (permethrin)??
? Steroids: Topical (in eczematised / nodular scabies)
? Keratolytics in crusted scabies
Failure of treatment

? Improper treatment (clothing, underneath the nails)

? Poor compliance

? House hold and/or institutional contacts not treated

? Resistance to drugs (lindane etc.)

Causes of itching even after treatment

Itching persists for few days even after successful

? Re-infection / relapse
? Eczematous reaction
? Contact irritation sensitization to acaricidal drugs
? Scabeitic nodules
? Other skin problems

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

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

Normal Habitat

? Pediculosis capitis:
Scalp hair of host
Children, Females>males
? Pediculosis corporis:
Clothing close to skin of host
Vagabond's disease - pigmentation of the skin caused

by long continued exposure, uncleanliness, and

especial y by scratch marks and other lesions due to

the presence of body lice
? Phthiriasis :
? Pubic, axillary, beard hair, eyebrows; eyelashes; hair

of trunk & limbs; rarely scalp margins.

? Sexually active young adults; in children due to

sexual abuse or parental contact.

Clinical features

Pediculosis capitis:
? Scalp pruritus
? Detection of nits / adults lice on scalp hair
? Secondary bacterial infection
? Cervical lymphadenopathy
? Matting of hair with pus and exudate - plica polonica
? Eczematization- neck /generalized
Clinical features

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

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

speckles on skin


Head lice: Topical treatment:






lotion, 1%


I application - day 9

Malathion 0.5% 8-10 hr /



Repeat after 10 days


Lindane 1%


minutes 2 applications (9-10 days)

Ivermectin lotion,




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

of the louse or a direct toxic effect on the louse

Body louse

? Difficult
? The most important treatment- disinfestation of all

clothing & bedding

? Beds should burned or sprayed with lice sprays-

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

? The patient should be treated from head to toe with

a topical insecticide or given oral ivermectin
Pediculosis pubis

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

hairy area of the body

? Crab lice are treated with the same topical therapy as

that for pediculosis capitis

Pediculosis : Treatment

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

This post was last modified on 07 April 2022