arthropods attacks i ihab younis, m.d
DESCRIPTION
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. - PowerPoint PPT PresentationTRANSCRIPT
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