Parasitic Skin Infections

parasitic skin infections

a parasite is an organism that depends on a living host for one or more   of   its

essential metabolic requirements

human scabies is a highly contagious infestation caused by the mite (sarcoptes scabiei var hominus).   adult mites are 0.3 mm long 

life cycle 

the mite infestation begins when a fertilized female mite arrives to skin surface, then burrow through the stratum  corneum at a rate of 3 mm per day, it lays about 3 eggs per day, eggs hatch within 3 days into larvae, which reach maturity in about 3 weeks.    the mite can survive for about 3 days outside the human skin . role of 3 

presentation

scabies incognito: is a modified scabies due to inappropriate use of   topical steroids.

crusted (norwegian) scabies: is a widespread crusted eruption with minimum or no itching  and vast numbers of mites. it affects people with neurological disorders, senile dementia, or immunosuppressed, and can be a source of epidemics of ordinary cabies.

transmission

transmission of the mite occurs usually through prolong (5-20 min) close contact, some infections can be from exposure to fomites.

history:

1. presence of nocturnal pruritus.

2. involvement of other members of the family.

3. history of prison, travelling or hospital admission for the patients or his close contacts.

examination:

1. involvement of the predilection sites.

2. detection of burrows, for better visualization put a dropinginginging of mineral oil or use blue or black ink then removed with alchohol swap.

3. dermatoscopy can be used to examine burrow and the mite in vivo.

4. wood s light also can be helpful (fluorescein solution fills the burrows and viewed.

investigation:

1. microscopical examination: of mites, eggs or its feces (scybala), usually within burrows. the mite can be picked with a needle from the end of its burrow and identified microscopically, eggs and mites can be seen in burrow scrapings mounted in koh or mineral oil.

2. skin biopsy can be diagnostic, the mite is found in the stratum corneum.

3. pcr in which the dna from the mite can be detected from cutaneous scales.

treatment:

1.        general principles:

a- treat all members of the family and sexual contacts, whether they are itching or not. b-   disinfect the clothing and bed linens (with boiled water) and not use them for 3 days.

c- the whole body should be covered with the medication. from below the jaw line, to the soles. face and scalp should be treated in infants.

2.        topical medications:

a- permethrine cream or lotion (5 % for adults and 2.5 % for children), applied for         8-14 h repeated after 1 week.  it is the treatment of choice. can be used in pregnant and lactating women and infants older than 2 months.

b- sulfur ointment (5% for infants and 10 % for adults) once each day for three days. safe in pregnant, lactating,  and infants. it is  messy, unpleasant odor, irritant and stain.

c- crotamiton (eurax):  is an antipruritic and scabicidal drug, once daily for 5 days.

d- gamma benzene hexachloride (lindane): applied for 8 h and repeated after 1 wk. not recommended for children, during pregnancy, or lactation

e- benzyl benzoate lotion 25 %.

3.        systemic medications:

ivermectine is an antihelminthic drug given in single oral dose (200 mg / kg), as a single dose and repeated after one week. indicated for refractory cases, scabies in institutions, and crusted scabies. 

lice infestations (pediculosis)

lice are flattened wingless insects.  pubic lice (crabs) are broader than scalp and body lice. two species are obligate parasites in humans: pediculus humanus (p. h. capitis, the head louse, and ph. corporis, the body louse) and phthirus pubis (the pubic louse).    adult mite are 3mm long.

life cycle:

the female louse lays eggs at a rate of 8 eggs per day.the eggs hatch within 8 days into larvae.the larvae transform into nymphs which become adult lice in 8 days. (role of 8)

clinical types:

head lice:

it is most common in children, and more in girls. the main symptom is itching. scratching and secondary infection soon follow and, in heavy infestations, the hair becomes matted and smelly. draining lymph nodes often enlarge. all patients with recurrent impetigo or crusted eczema on their scalps should be carefully examined   for the presence of nits .

spread is achieved by head-to-head contact, and perhaps by shared fomites.

body lice:

body louse infestations are now uncommon except in the unhygienic and socially deprived. self-neglect is usually obvious against this background there is severe and widespread itching, especially on the trunk.

transmission is via infested bedding or clothing.

vagabond’s disease is a chronic untreated disease in which the skin becomes generally thickened, eczematized and pigmented lymphadenopathy is common.

body lice can transmit typhus, relapsing fever, and trench fever.

pubic lice:

it is the most contagious sexually transmited infections. most commonly infest young adults. severe itching with excoriations in the pubic area is followed by eczematization and secondary infection. a small blue-grey macules of altered blood at the site of bites may be seen. pubic lice may spread extensively in hairy males (for thighs and abdomens).

eyelash infestation:

almost exclusively in children, may acquired from other children, or from infected adult with pubic lice (may be a sign of sexual abuse).

diagnosis:

1. clinical signs and symptoms.

2. examination of the scalp may show few adult lice which are gray and hard to find, but the nits are many and easily detected. nits should  be differentiated from simple scales (the nits are oval, shiny, firmly attached to one side of the hair (45°) close to the skin, with positive click sign). nits seen more easily with wood s light or under microscope.

in body lice infestation the seams of patient s clothes should be examined for nits detection.

treatment:

general measures: household members and those in close contact should be screened and treated as necessary. fomite control is important to prevent reinfestation. all types of medications should be repeated after 7-10 days.

topical medications:

permethrin cream 1% (nix) it is the most effective treatment. it paralyzes the nerves  that allow the lice to breathe. it is applied on the scalp for 10 minutes, after the hair is shampooed and dried.

  pyrethrin  solution shampoo applied for 10 minutes.

malathion lotion has residual activity one treatment is suffiecient for 8-12 hours second application usually not needed. not recommended for infants.

lindane 1% shampoo

systemic medications:

ivermectin cause paralysis and death of lice. single dose of   200mg/kg .

methoprim twice daily for 3 days (killing the essential bacteria in the gut of the louse).

treatment of eyelashes infestation:

the most practical and effective treatment is petrolatum (vaseline) three times daily for     5 days. fluorescein dropingingingings 10-20% is other option. ivermectin used for resistant cases.

cutaneous leishmaniasis

life cycle:  female phlebotomous sandfly (vector) ingests amastigotes while taking a blood meal from the skin of a man or other mammals (reservoir). amastigotes transform into promastigotes in the vector’s gut, then the sandfly inject it into skin of a human (host).   promastigotes become amastigotes and taken by the macrophages within which they multiply and the cycle may be repeated again.

clinical types of leishmaniasis:

1.  cutaneous leishmaniasis (cl), including: old world cl and new world cl.

2.  mucocutanous leishmaniasis.

3.  visceral leishmaniasis (kala-azar).

old world cutaneous leishmaniasis: (baghdad boil, delhi boil, little sister).

it   is caused by l. major, l. tropica, l. aethiopica and l. infantum.

epidemiology:

old world  include the mediterranean basin, southern europe, africa, and asia.

over 90% of cl cases occur in afghanistan, algeria, iran, iraq, saudi arabia, syria, and peru. cl is an endemic disease in iraq. children are the commonest age group affected since immunity is acquired from the initial infection.

clinical features:

incubation period is variable (average: 2-3 months).  onset is insidious and usually at autumn or winter. the predilection sites are the exposed parts especially face, lower limbs, and hands. characteristics of lesions: dusky red colour, indurated, painless and non-tender nodules, involving the exposed parts, with slow evolution.

two variants are described:

wet (ulcerative, rural) type: caused by l. major. the ip less than 2 months. healing within 2 - 6 months (rapid course).  residual scar larger and deeper that of dry type.

dry (non ulcerative, urban) type: caused by l. tropica. the ip is more than 2 month. healing within 8-12 months (longer course). residual scar smaller and more superficial.

diagnosis:

in endemic areas, the clinical diagnosis is not difficult, confirmed by the presence of one or more of the following criteria:

1. history: of sandfly bites in the previous weeks or months.

2. examination: non-healing chronic nodular, violaceous ulcer (more than one month).

3. smear: demonstration of amastigotes in giemsa-stained smears.

4. biopsy: demonstration of intracellular amastigotes (leishman-donovan , ld, bodies)

  and leishmanial granulomas.

5. culture: growth of promastigotes in nnn medium.

6. pcr: demonstration of leishmanial dna.

7. leishmanin test (montenegro test): injection of 0.1 ml suspension of cultured promastigotes in the forearm, and   read after 48-72 h. it is unreliable in endemic areas.

leishmaniasis recidivans (chronic leishmaniasis):

brown-red or brown-yellow papules appear, usually close to a scar of an old  (mother) lesion of cutaneous leishmaniasis. it may persist and spread slowly for many years. the number of parasites is scanty. leishmanin test is strongly positive.

post-kala-azar dermal leishmaniasis (pkdl) (dermal leishmanoid):

begins during disease convalescence, appearing on the face, forearms, and lower limbs, as discrete papules, which on histological examination show scanty parasites. the leishmanin test is positive. the rash heals spontaneously over a few months.  

recurrent leishmaniasis:

infection by leishmaniasis usually gives lifelong immunity but recurrent infection may occur in: immune suppressed, elderlies, very early treatment, infection with a new strain.

treatment:

cl is self-limited infection, the most important indications of treatment is: cosmetic concern, controlling the disease in population, failure of spontaneous healing.

topical therapy:

topical paromycin (an aminoglycoside antibiotic) or ketoconazole cream.

intralesional infiltration:

1. sodium stibogluconate solution pentostam^®: is the treatment of first choice in cl. it is injected in the borders of the lesions at weekly intervals until cure.

2. zinc sulfate solution (2%)

3. hypertonic sodium chloride solution (7%)

4. interferon- gamma (perilesional): effective but expensive

physical therapy:

infrared heat, cryotherapy, surgical excision or curettage (rarely used now).

systemic therapy:

parentral:

1. sodium stibogluconate: a pentavalent antimonial compound considered as the 1^st choice systemic agent in treatment of cl. dose: 20 mg/ kg / day for 28 days given in two divided daily doses i.v. or i.m.. although uncommon, cardiotoxicity is the most serious side effect (it should be given under ecg monitoring).

2. meglumine antimoniate

3. amphotericin b: may be used in antimony-resistant cases.

oral:   

zinc sulphate 10 mg /kg, dapsone, ketaconazole, rifampicin. itraconazole and allopurinol.

indications of systemic therapy:

1.  multiple or large lesions.

2.  lesions in an immunocompromized patient.

3.  lesions in a critical area (around eyes), or in disfiguring or painful areas (nose & ears).

4.  l. recidivans.

"best regards"