Arthropods Attacks I IHAB YOUNIS, M.D.

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Arthropods Attacks IIHAB YOUNIS, M.D.
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Scabies

• Etymology L. scabo, to scratch

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History

• " The seven year itch" was first used with
• reference to persistent,undiagnosed
  infestationswith scabies
• Scabies has been reported for more than 2500
  years

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• 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

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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

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Causative agent

• The Female Gravid
• Sarcoptes scabiei mite,
• var hominis
• G sarx (the flesh) and
• koptein (to cut)

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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

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• 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

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• 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

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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

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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

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• 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

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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

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• Scabies in infants tends to be more disseminated
  affecting head and face
• Geriatric scabies demonstrates a propensity for
  the back, often appearing as excoriations

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• 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

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

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• 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

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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

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• 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

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• 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

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• 3-Scabies in the clean
• The disease is easily misdiagnosed because
  lesions are sparse and burrows are difficult to
  find

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• 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

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• 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

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• 6-Bullous scabies
• May mimic bullous pemphigoid clinically,pathologi
  cally, 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

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complications

• Secondary bacterial infection may occur
• Nephritogenic
• streptococcal
• strains may
• colonize
• scabietic lesions,
• leading to acute
• glomerulonephritis

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

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Immunology

• DelayedT-lymphocytes in inflammatory lesions
• High IgG, IgM and IgA returning to normal after
  treatment
• IgM and C3 deposits at the DE junction in burrows

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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

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• 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

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Treatment
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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 lt2 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

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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

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• 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 pregnancyB - Usually safe but benefits
  must outweigh the risks

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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

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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

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Benzyl benzoate(Benzanil)

• Neurotoxic to mites
• Use 25 emulsion apply below neck 3 times within
  24 h without an intervening bath
• Safety in pregnancyX - Contraindicated in
  pregnancy
• May cause stinging, if so reduce concentration

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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

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Pediculosis

• Etymology L. pediculus louse
• G. -osis condition

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Types

• Pediculosis capitis
• Pediculosis corboris
• Pediculosis pubis

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• Pediculosis capitis

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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

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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

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• 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

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• 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 Woods lamp empty
• nits are fluorescent gray

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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

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• Pediculosis corporis

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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

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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

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• 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

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• 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

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• Pediculosis pubis

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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

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Causative agent

• Pthirus pubis (pubic or crab louse)
• It is much shorter than other lice, being almost
  as wide as it is long

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• 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

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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

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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

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Treatment
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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

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• 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

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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

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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

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• 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

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• 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)

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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

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• Mercuric oxide Ointment (1) is treatment of
  choice for Phthirus palpebrarum
• Inspect eyelids and remove nits mechanically
• Apply to eyelashes qid for 14 d

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• 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

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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

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• 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

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