Arthropods Attacks I IHAB YOUNIS, M.D.

1. Arthropods Attacks IIHAB YOUNIS, M.D.

2. Scabies Etymology: L. [scabo,] to scratch

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

4. 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

5. 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

6. Causative agent The FemaleGravid Sarcoptes scabiei mite, var hominis G: sarx (the flesh) and koptein (to cut)

7. 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

8. 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

9. 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

10. 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

11. 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

12. 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

13. 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

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

15. 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

18. Histopathology

19. 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

20. 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

21. 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

22. 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

24. 2-Animalscabies • 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

25. 3-Scabies in the clean • The disease is easily misdiagnosed because lesions are sparse and burrows are difficult to find

26. 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

27. 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

28. 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

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

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

31. 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

32. 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

33. 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

34. Treatment

35. 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

36. 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

37. 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

38. 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

39. 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

40. 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

41. 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

42. Pediculosis Etymology: L. [pediculus] louse + G. [-osis] condition

43. Types • Pediculosis capitis • Pediculosis corboris • Pediculosis pubis

44. Pediculosis capitis

45. 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

46. 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

47. 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

48. 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

49. 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