Arthropods Attacks I

IHAB YOUNIS, M.D.

Scabies

Etymology: L. [scabo,] to scratch

History

" The seven year itch" was first used with

reference to persistent,undiagnosed infestationswith scabies

Scabies has been reported for more than 2500 years

Aristotle discussed “lice in the flesh”

Celsus recommended sulfur mixed with liquid pitch as a remedy for the disease

The disease was first ascribed to the mite by Bonomo in 1687

It was the first human disease recognized to be caused by a specific pathogen

Etiology

About 300 million cases occur annually

Prevalence is higher in children and sexually active individuals

It affects persons of all ages, races, and socioeconomic groups

Causative agent

The Female Gravid

Sarcoptes scabiei mite,

var hominis

G: sarx (the flesh) and

koptein (to cut)

Life cycle

The entire life cycle of the mite lasts 30 days and is spent within the human epidermis

After copulation, the male mite dies and the female mite burrows into the superficial skin layers and lays a total of 60-90 eggs

The ova require 10 days to progress through larval and nymph stages to become mature adult mites

Mites can survive up to 3 days away from human skin, so fomites such as infested bedding or clothing are an alternate but infrequent source of transmission

Mites move through the top layers of skin by secreting proteases that degrade the stratum corneum creating burrows

They feed on dissolved tissue but do not ingest blood

An affected individual harbors a variable number of living mites (10-15(

In immunocompromised hosts the number of mites can exceed 1 million (crusted scabies)

Symptoms appear 2-6 weeks after infection as delayed-type IV hypersensitivity reaction to the mites, eggs, and scybala (packet of feces) occurs

In reinfestation, the sensitized individual may develop a reaction within hours

Mode of transmission

Epidemics or pandemics may occur in 30-year cycles

Transmission is predominantly through direct skin-to-skin contact(10 minutes)

Indirect contact through fomites such as infested bedding or clothing is possible, although not usual

Clinically The history is very important

Intractable pruritus that is worse at night

Similar symptoms in close contacts

History of itching for a short time. On the other hand, the infestation can persist indefinitely

Occurs more commonly in fall and winter

A short (2-3 mm), elevated, serpiginous , gray brown track in the superficial epidermis, known as a burrow, is pathognomonic

Occasionally, the mite is visible to the naked eye as a small white dot

A small vesicle or papule may appear at the end of the burrow

Distribution

Any pruritic papule on

the penis or female

areola of breast

or palms & sole

of foot in an

infant is scabies

until proved

otherwise

Scabies in infants tends to be more disseminated affecting head and face

Geriatric scabies demonstrates a propensity for the back, often appearing as excoriations

One- to 3-mm erythematous papules and vesicles are seen in typical distributions in adults and most likely represent a hypersensitivity reaction

In very young children and infants, a widespread eczematous eruption primarily on the trunk is common

Histopathology

If a burrow is excised, mites, larvae, ova, and feces may be identified within the keratinA superficial and deep dermal infiltrate composed of lymphocytes, histiocytes, mast cells, and eosinophils Spongiosis and vesicle formation with exocytosis of eosinophils

Crusted scabies demonstrates massive hyperkeratosis of the stratum corneum with innumerable mites in all stages of development

Psoriasiform hyperplasia of the underlying epidermis with spongiotic foci and occasional epidermal microabscesses is present

Types

1-Crusted Scabies (Norwegian): First described in 1848 by Danielssen and

Boeck, who considered the disease to be a form of leprosy endemic to Norway

May occur in almost any area of the body including the scalp

Occurs in immunocompromised persons and in weak patients who can not scratch

Extensive, widespread, crusted lesions appear with thick, hyperkeratotic scales over the elbows, knees, palms, and soles

Itching is minimal

Serum IgE and IgG

levels are extremely

high

2-Animal scabies is characterized by absence of burrows since

the animal mites cannot adapt themselves to human skin

It is not transmitted from one human being to another

3-Scabies in the clean The disease is easily misdiagnosed because

lesions are sparse and burrows are difficult to find

4-Scabies incognito Topical or systemic steroids may mask

symptomsand signs of scabies, although the infestation remains freely transmissible

This often results in unusual clinical presentations such as atypical and widedistribution

5-Nodular scabies Reddish-brown, pruritic nodules on covered parts (most frequently the male genitalia, groin, and axillary regions) Probably represents a hypersensitivity reaction to retained mite parts or antigens

6-Bullous scabies May mimic bullous pemphigoid clinically,

pathologically, and immunopathologically Most patients are over 65 years of age. The

duration of the scabies from onset until diagnosis is weeks to months, thereby exposing a number of individuals to the disease

Burrows are present in most cases

complications Secondary bacterial infection may occur Nephritogenic

streptococcal

strains may

colonize

scabietic lesions,

leading to acute

glomerulonephritis

Eczema, particularly in atopics, may be prominent in the active scabies and may continue as eczema after the scabies has cleared

Acarophobia

Immunology Delayed:T-lymphocytes in inflammatory

lesions High IgG, IgM and IgA returning to normal

after treatment IgM and C3 deposits at the DE junction in

burrows

Lab tests Skin scraping: Place a drop of mineral oil on

a glass slide, touch a No. 15 blade or a 7-mm curette to the oil, and scrape infested skin sites, preferably primary lesions such as vesicles, juicy papules, and burrows

cover with a coverslip, and examine under a

light microscope at 40X magnification

Multiple scrapings may be required to identify mites or their products. Persistence is key to accurate diagnosis

Crusted scabies: Add 10% potassium hydroxide (KOH) to the skin scraping. This dissolves excess keratin and permits adequate microscopic examination

Treatment

Permethrin cream 5% (Ectomethrine) Causes respiratory paralysis of parasite Recommended by CDC as first-line therapy Apply from chin to toes and shower off 10-12 h

later; repeat in 1 wk Not recommended for children <2 mo C - Safety for use during pregnancy has not

been established More effective than a single dose of oral

ivermectin, although it has equivalent efficacy when 2 doses of ivermectin are used at time zero and 2 weeks later

Lindane (Scabene)

Stimulates nervous system of parasite, causing respiratory paralysis

Second-line treatment if other agents fail or are not tolerated

Not very safe in children as transcutaneous absorption leading to neurotoxicity

Apply thin layer from chin to toes; use on dry skin and shower off 10 h later; repeat in 1 wk

Infants and children: Apply as adults but leave on 6-8 h before washing off and do not exceed 30 g/application

Oil-based hairdressings may increase toxicity Safety in pregnancy:B - Usually safe but

benefits must outweigh the risks

Sulfur in petrolatum (2 -10%, with 6% preferred)

May be used safely without fear of toxicity in very small children and in pregnant women

It is malodorous, stains clothes & requires repeat applications, thus reducing compliance. It can cause a dermatitis in hot and humid climates

Apply to entire body below head on 3 successive nights and bathe 24 h after each application

Crotamiton (Eurax)

Mechanism of action is unknown Apply thin layer onto skin of entire body from

neck to toes; repeat in 24 h; take a cleansing bath 48 h after last application

Do not apply to face, urethral meatus, eyes, mucous membranes, or swollen skin; can cause seizures

Benzyl benzoate(Benzanil)

Neurotoxic to mites Use 25% emulsion; apply below neck 3 times

within 24 h without an intervening bath Safety in pregnancy:X - Contraindicated in

pregnancy May cause stinging, if so reduce

concentration

Ivermectin (Ivactin 6 mg tab) Binds selectively with glutamate-gated

chloride ion channels in invertebrate nerve and muscle cells, causing cell death

2 mg/10kg/d PO as single dose May cause nausea, vomiting, and mild CNS

depression; may cause drowsiness

Pediculosis

Etymology: L. [pediculus] louse +

G. [-osis] condition

Types

Pediculosis capitis

Pediculosis corboris

Pediculosis pubis

Pediculosis capitis

Etiology The disease is spread from person to person

by close physical contact or through fomites (eg, combs, clothes, hats, linens)

Overcrowding encourages the spread of lice

Head lice are very rare among negros due to the twisted nature of the hair shaft

Causative agent Pediculus humanus capitis (head louse) Lice are ectoparasites that feed on human

blood several times daily They have claws on their legs that are

adapted for feeding and clinging to hair or clothing

They move quickly(up to 23 cm/min) , which explains their ease of transmission

A fertilized female louse lays about 10 eggs a day for up to a month until it dies

The eggs (nits) are attached to the hair shaft, close to the skin surface, where the temperature is optimal for incubation

Nits are cemented to the hair shaft with chitin and are very difficult to remove. Nits can survive for up to 10 days away from the human host

The eggs hatch in about 6-10 days Lice develop into adults

in 19 to 25 days from the time the egg is laid Live nits are fluorescent white when

illuminated with

a Wood’s lamp; empty

nits are fluorescent gray

Clinically Itching is the most common symptom Erythema and scaling may be present, as

well as pruritic papules on the posterior neck There may be linear excoriations at the

periphery of the hair area which frequently lead to pyoderma

Cervical lymphadenopathy and febrile episodes are not uncommon

Pediculosis corporis

Etiology Infestations of body lice are found mainly in

those with low income and poor hygiene, and homeless persons and refugees living incrowded conditions

The infestation is transmitted chiefly by contaminated clothing or bedding

Causative agent Pediculus humanus corporis (body louse) It is similar to the head louse but a little larger Body lice and their eggs are predominantly

found on clothing and should be looked for in the seams of clothes

Early lesions consist of macules or papules at the site where the louse punctures the skin to obtain blood

The characteristic eruption consists of numerous vertical excoriations, especially on the trunk and neck, caused by intense itching

Crusts and at times pus or serum may stain the underclothing

Transitory wheals and bacterial infections may complicate the process

Postinflammatory pigmentation is common

Few or no adult organisms are seen except in heavily infested persons

Nnumerous nits are found in clothing seams, particularly in contact with the crotch, armpits, belt line, and collar

Pediculosis pubis

Etiology It is typically transmitted sexually, frequently

coexisting with other sexually transmitted diseases

Pubic lice were found in 1.7% of men and 1.1% of women in an STDs clinic

Causative agent Pthirus pubis (pubic or crab louse) It is much shorter than other lice, being

almost as wide as it is long

Lice have three pairs of legs. In the crab louse, the first set of legs terminates in a slender claw, while the second and third pairs have well-developed claws perfectly adapted for grasping the coarse, widely spaced hairs of the pubis

It is sluggish,

travelling a maximum

of 10 cm/day

Clinically Pubic hair is the most common site The crab louse is found firmly attached to

the base of the pubic hair. Nits may also be found

Pubic lice may spread to hair around the anus, abdomen, axillae, chest, and eyelashes

Bluish grey macules, or maculae cerulea, may be seen on the abdomen or thighs and are secondary

Diseases transmitted by lice Typhus: Caused by Rickettsia prowazekii

high fever, petechial rash,CNS involvement Trench fever: Caued by Bartonella quintana

fever similar to typhus, infective endocarditis Relapsing fever: Caused by the spirochete

Borrelia recurrentis relapsing fever,rash

Treatment

General measures Nits are best removed with a very fine comb Soaking the hair in a solution of equal parts

water and white vinegar and then wrapping the wet scalp in a towel for at least 15 minutes may facilitate removal

Treat all family members Discard infested clothing or wash in very hot

water

Shaving of the scalp or body hair eradicates lice; if cosmetically acceptable by the patient

Wet combing or application of diluted vinegar or commercial preparations of 8% formic acid may help in the removal of nits or at least make the combing easier. Plastic or the sturdier metal nit combs may be used

Multiple lice suffocation agents have been advocated, but most have not been scientifically evaluated. These include Vaseline; petroleum jelly; oils; mayonnaise

Drug therapy Treatment should be repeated in 7-10 days

(the time needed for the eggs to hatch) because nits are less effectively killed than adults

All contacts should be treated simultaneously Resistance to pediculicides has increased

over recent years. Therapeutic agents can be rotated to slow the emergence

Same drugs as for scabies but: Permethrin 5% :leave 5-10 min, then rinse

Lindane 1% shampoo: Apply to dry head or pubic hair and surrounding areas; allow to set for 4 min, then lather for 4 min and rinse; repeat in 7 d prn

Malathion (Prioderm) : Irreversible cholinesterase inhibitor that is hydrolyzed and, therefore, detoxified rapidly by mammals but not by insects causing respiratory paralysis

Ovicidal and pediculicidal. Binds to hair and provides some residual protection after therapy

Available as 0.5% and 1% lotion

Apply lotion to dry hair; leave on 8-12 h, rinse; repeat in 7 d prn(as needed)

Contains flammable alcohol; do not expose lotion or wet hair to open flame or electric heat, eg, hair dryers (allow hair to dry naturally and uncovered following application); avoid contact with eyes (flush eyes immediately with water if contact)

Trimethoprim-sulfamethoxazole The mechanism of action is postulated to be

ingestion of the antibiotic by the louse as it takes its blood meal; subsequently the antibiotic kills the gut flora of the louse, with death ensuing from a deficiency of B vitamins

The combination of permethrin and trimethoprim-sulfamethoxazole was more effective than either agent alone

Mercuric oxide Ointment (1%) is treatment of choice for Phthirus palpebrarum

Inspect eyelids and remove nits mechanically

Apply to eyelashes qid for 14 d

Kerosene has shown pediculicidal activity in vitro, but safety and efficacy remain to be evaluated

DDT was the first pediculicide widely available. It was the main agent used in the treatment of body lice infestations during World War II. It was banned in the 1970s but about to be reintroduced as pesticide

Treatment failures Drug resistance Improper dilution or duration of

application Reinfestation from untreated contacts It may be best to assume that no product

is reliably ovicidal and that patients will not comply fully with instructions. Retreatment in 1 week to 10 days is advisable to kill recently hatched nymphs

Drugs are often applied to wet hair, which dilutes the product and protects lice as they reflexively close their respiratory spiracles when exposed to water

Hair conditioners may coat the hair shafts and prevent pediculicides from binding adequately to the hairs

Lice have been in existence for thousands of years. Their extinction seems no more likely than our own