Download MBBS (Bachelor of Medicine, Bachelor of Surgery) Dermatology PPT 23 Scabies Pediculosis Lecture Notes
Cutaneous Infestations:
Scabies, Pediculosis
Definition
?Scabies - common parasitic infestation caused by the
`itch'-mite: Sarcoptes scabiei var. hominis
?Sarcoptes scabiei var. canis (dogs); Notoedres cati
(cats)
Epidemiology
? 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
?Overcrowding
?Immuno-compromised
?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
(male)
?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) ??
Transmission
? 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
products
? 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
line
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
Complications
? Secondary infection
? Eczematization
? Glomerulonephritis
? Phimosis, Paraphimosis
? Urticaria
? Erythroderma
? Drug reactions: irritation, eczematization
Investigations
? Scraping: from papule, burrow to demonstrate mite,
egg,
? Dermatoscopy is useful for detecting burrows and
visualizing their contents
? IgE- specific levels
? Newer: Polymerase chain reaction, Immunosorbent
assays? not available widely
Treatment-principles
? 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
neurotransmission
? 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
AND
? 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
treatment
? Re-infection / relapse
? Eczematous reaction
? Contact irritation sensitization to acaricidal drugs
? Scabeitic nodules
? Other skin problems
Pediculosis
? 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
Phthiriasis:
? Nocturnal pruritus
? Detection of nits & louse on affected hair
? Blue grey macules (maculae caerulae) / Rust coloured
speckles on skin
Pediculocides
Head lice: Topical treatment:
Drug
Dose
Remark
Permethrin
10
lotion, 1%
minutes
I application - day 9
Malathion 0.5% 8-10 hr /
lotion
20
Repeat after 10 days
minutes
Lindane 1%
4-5
minutes 2 applications (9-10 days)
Ivermectin lotion,
10
0.5%
minutes
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,
application.
? Eyelash infection (phthriasis palpebrum):
Mechanical removal, Epilation, Topical agents
This post was last modified on 07 April 2022