Scabies

Parasitic Infection

By
Dr. Hala- Al- Salman
M.B.Ch.B., F.I.B.M.S.

Scabies

A common skin disease with a worldwide distribution.
Cause: Sarcoptes scabiei var. hominis.
The adult mites are 0.3-0.4 mm long. It is an obligatory parasite to human. The mite cannot survive away from the skin more than a few hours.
Once the mite affect the skin, the fertilized female burrow through the stratum corneum at a rate of 2 mm per day and produce 2-3 eggs each day, then these eggs change to a sexually mature mites in 2-3 weeks.
The number of the mites varies from case to case, from less than 10 in clean adult to many more in unwashed child.
The generalized eruption of scabies and its itchiness are thought to be caused by a sensitization to the mites or their products.

Transmission:

Most commonly by close bodily contact, or by the use of contaminated towels, bed linins, and clothing.
Rarely dogs and cats may be a source of infection.

Clinically:

Scabies characterized by pruritic papular lesion and burrows (which contain the female mite and her young).
For the first 4-6 weeks there may be no itching, but thereafter, pruritus dominates, which is very severe at night but tolerable at day time, usually affecting several members of the family.


Lesion:
Non-specific: excoriated, eczematized or urticarial papules on the trunk.
Specific: Burrows, which is grey-whitish scaly tortuous lines up to 1 cm length, on the sides of the fingers, fingerwebs, side of the hands, wrists, elbow, axilla, nipple, around the umbilicus, ankles, feet, and genitalia.
Face, palm and soles are affected only in infants.

Complications:

Secondary infection.
Irritation and eczema result from repeated application of scabicides.
Post scabitic nodules (persistent itchy red nodules may remain for months mainly in the genitalia in adults and trunk and axilla in children).
Other venereal diseases.

Differential Diagnoses:

papular urticaria.
atopic dermatitis.
chronic urticaria.
lichen planus.
neurotic excoriations.
dermatitis herpitiformis.

Diagnosis:

Clinical picture.
Identification of the mites:
* The mite can be picked with a needle from the end of the burrow.
* Scraping the burrow and examine the content under microscope to see the eggs and mites.


Treatment:
* Treat all the family members and sexual contact, whether they itch
or not.
* The treatment should apply to all area of the skin below the jaw line.

Permethrin cream 5%.(children & adult)

Benzyle benzoate lotion 25%.
Precipitated sulphur 5-10%.(all ages)
Lindane (gamma benzene hexachloride) (neurotoxic in children).
Crotamiton cream (eurax).
Resistant, non-responding cases: Ivermectin (single oral dose).

Pediculosis (Lice infestations)

Lice are ectoparasites, because they live on, rather than in, the body. They are flattened wingless insects that suck blood. Their eggs (nits) attached to hair and clothing.
The main feature of all lice is severe itching followed by scratching and secondary infections.
There are 3 clinical types depending on the species of the lice:

I. Pediculosis capitis (Head lice):

Still a common disease, found worldwide affecting up to 10% of children.
Cause: Pediculus humanus capitis.
The head lice are 3-4 mm length, grayish often hard to find, but its eggs (nits) can be seen easily. They are 0.8 mm and firmly cemented to the bases of the hair shaft close to the skin to acquire adequate heat for incubation. The eggs hatch in 8 days.


Transmission:
From person to person by head-to-head contact and by shared combs or hats.

Clinically:

The main symptom is itching start around the sides and back of the scalp then become more generalized over the scalp. Then scratching and secondary infections soon follow and in heavy infestation the hair become matted and smelly with lymphadenopathy.

Complications:

secondary bacterial infection.
severe cases may associated with constitutional symptoms.

Differential Diagnoses:

impetigo.
crusted eczema.
scales and dandruff.
seborrhiec dermatitis.
psoriasis.

Treatment:

Malathionlotion 0.5% (kill lice & eggs, applied for 8-12hr.)
Permethrin cream, (paralyse the nerve of lice, rinsed out after 10 min.).
Pyrethrin (liquid, gel and shampoo, applied for 5 min.).
Lindane 1% shampoo.
Antibiotics.
Ivermectin (resistant cases).


Notes:
1. The medications should be applied to dry hair (lice close the
respiratory parts in water).
2. Treatment repeated after a week.
3. Other members should be checked and treated.
4. Fin-toothed comb help to remove the nits.

II. Body lice (pediculosis corporis)

Cause: Pediculus humanus corporis.
Uncommon disease, it is a disease of unclean. It cause the spread of typhus, relapsing fever and trench fever during wartime and in underdeveloped countries.
Body lice live and lay their nits in the seems of clothing and return to the skin surface for feeding.

Transmissin: Infested bedding and clothing.

Clinically:
Self-neglect is obvious. There is severe and wide spread itching on the trunk.
The lesions appear as pinpoint redness due to the bite, small papules, wheals and excoriations. The bites themselves are soon obscured by excoriations and crusts of dried blood or serum.
Chronic untreated cases (Vogabond's disease) The skin become generally thickened, eczematized and pigmented.
Lymphadenopathy is common.

Differential Diagnoses:

scabies.
eczema.
pruritus due to systemic disease (e.g. lymphoma).


Treatment:
Treat the infested clothing and bedding, lice and eggs can be killed by high temperature laundering.
Permethrin cr. 5%.
Lindane lition 1%.

III. Pubic lice ( pediculosis pubis)

Cause: Phthirus pubis.

Transmission: Most commonly by sexual contact, rarely from clothing and bedding.

It affects young adults mainly, both sexes.
It can affect children mostly on the eyelashes and eyebrows.

Clinically:

Severe itching in the pubic area, followed by eczematization and secondary infection.
Small blue-grey macules of altered blood can be seen at the site of bites.
The shiny translucent nits are less obvious than those of head lice.
It can affect any hairy area of the body, causing irritation on the trunk, thigh, and axilla.

Treatment:

permethrim and malathion. (Repeated after 1 week).
Eyelashes:
* Removal (painful).
* Apply thick layer of petrolatum twice daily for 2 weeks.
* Aquous malathion.


Leishmania
Cutaneous.
Mucocutaneous.
Visceral (kala azar).

Cutaneous Leishmaniasis

Localized skin infection, prevalent in tropical and subtropical countries. It affect all races, both sexes, all ages but most commonly children and young adults. Occur most commonly in the exposed parts (mainly the face).
Transmission: Sandfly (phlebotomus).
Cause: Leishmania tropica.
Epidemiology: endemic in Asia and many countries around Mediterranean Sea (Iraq, Iran, Saudia Arabia).

One attack will give permanent immunity in most cases, so in some endemic area deliberate inoculation of the parasite is done in the thigh to prevent scarring on the face, which is the commonest site of affection.

Clinically:

Moist (rural) type: Slowly growing indurated papule, which enlarge in a few months to form a nodule, which may ulcerate in a few weeks to form an ulcer that may reach up to 5 cm in diameter. Spontaneous healing occurs within 6 months, leaving characteristic scar. The incubation period is relatively short about 1-4 weeks.

Dry (urban) type: This has longer incubation period (2-8 months), develops much more slowly, and heal more slowly.

Diagnosis:

Clinical picture.
Smear (from the edge).
Culture of tissue fluid (NNN media).
Leishmanin intradermal test (positive after 3 months).
Histopathology (skin biopsy) show granulomatous reaction with leishman-donovan bodies with macrophages.
Polymerase chain reaction.


Differential Diagnoses:
Early stage before ulceration:
keloid.
keratoacanthoma
leprosy.
sarcoid.

Late stage after ulceration:

skin tumor (BCC, SCC).
T.B.
other granulomatous diseases.

Treatment:

Spontaneous healing occurs within 12-18 months.

Aim of treatment:

Avoid disfiguring scar in exposed area (face).
Avoid secondary infection.
Control the disease in the population.
Failure of spontaneous healing especially in diffuse type (persist 20-40 years if not treated).


Localized solitary lesion:
Intralesional sodium stibogluconate antimony preparation (pentostam), safe and effective.
Cryotherapy.
Local heat.
Laser ablation.

Multiple dissiminated lesions, area difficult to inject, and immunocompromized patients:

Systemic therapy: pentostam 20 mg/ kg for 28 days.
Others: Rifampicin, Dapson, ketoconazol









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