Ectoparasites Notes


Osmosis High-Yield Notes

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Pediculus humanus and Phthirus pubis (Lice)

Sarcoptes scabiei (Scabies)

NOTES NOTES ECTOPARASITES GENERALLY, WHAT ARE THEY? PATHOLOGY & CAUSES ▪ Ectoparasites: arthropods that live on outside of host, extract nutrients at host’s expense ▫ Uncommon: viable parasites transferred without direct host contact RISK FACTORS DIAGNOSIS OTHER DIAGNOSTICS History ▪ Including close contacts/living quarters Physical examination ▪ Dermatologic examination ▪ Commonly poor hygiene, close living quarters TREATMENT MEDICATIONS COMPLICATIONS ▪ Predicated on individual’s immune status, housing situation ▪ Topical neurotoxins, topical/oral parasidal drugs OTHER INTERVENTIONS SIGNS & SYMPTOMS ▪ Pruritus, bite marks, visible body parasites ▪ Proper hygiene, household measures, isolation (if necessary) PEDICULOSIS CORPORIS, CAPITIS, AND PUBIS (LICE) PATHOLOGY & CAUSES ▪ Infestation of easily transmissible sucking lice species ▫ Commonly in hairy bodily areas, characterized by local pruritus ▪ Sucking lice infection ▫ (Phylum) arthropoda → (class) insecta → (order) phthiraptera → (suborder) anoplura → (family) pediculidae/ pthiridae PATHOLOGY ▪ Lice live human hair → suck blood for nutrients ▫ Bite → saliva injection → anticoagulation effect, ↑ histamine release → maculae cerulea (blue/copperhued bite marks); pruritus OSMOSIS.ORG 375
▪ Lice require humans for nutritional source (parasites) ▫ Most climates allow mature louse 24 hours of viable life away from human source Transmission ▪ Physical contact ▫ Ideal location: slow-moving, parallel hair fibers ▫ Louse on one hair fiber → transfer to another individual’s hair → lay nits (eggs) on hair 1–2mm off of scalp → nymphs hatch within one week → mature over one week → female lice lay eggs for one month ▪ Fomites TYPES ▪ Pediculus humanus capitis → head louse ▫ Can survive 24–48 hours without blood meal/separated from host ▪ Pediculus humanus humanus → body louse ▫ Larger than head louse; can survive < 72 hours without blood meal ▪ Phthirus pubis → pubic louse ▫ AKA crab louse; can spread to body RISK FACTORS ▪ School-aged children ▪ Homeless population ▪ Refugee population (if living in close quarters) COMPLICATIONS ▪ Co-infections (also carried by louse) ▫ Bartonella quintana → endocarditis ▫ Epidemic typhus ▫ Louse-borne relapsing fever ▫ Trench fever ▪ Adolescents with pubic lice → ↑ gonorrhea/ chlamydial infection risk ▪ Pruritus → skin excoriation → secondary infection ▫ Commonly staphylococcal infection SIGNS & SYMPTOMS ▪ Site pruritis (head, body, pubis) 376 OSMOSIS.ORG DIAGNOSIS OTHER DIAGNOSTICS Dermatologic examination ▪ Examination of hair follicles, clothing seams ▪ Nits: more visible than nymphs/lice; most visible (white) after louse released from egg; does not dislodge easily from hair follicle ▪ Body louse → widespread dermatitis ▪ Often linear excoriations ▪ Maculae ceruleae → may have punctal hemorrhages → recent bites ▪ Hyperpigmentation/lichenification → older bites Lymph node examination ▪ Capitis infection → posterior lymphadenopathy TREATMENT MEDICATIONS Topical benzyl alcohol ▪ Mechanism of action → louse asphyxiation ▫ Difficult for resistance to develop Neurotoxic agents ▪ Resistance develops with ▫ Pyrethrin: botanically-derived neurotoxin ▫ Permethrin: Na+ channel blocker → paralysis → death ▫ Malathion: organophosphate cholinesterase inhibitor OTHER INTERVENTIONS Hair shaving ▪ Eradicate current infection Mechanical removal ▪ Wet combing → tedious, poor compliance ▫ Pre-treatment: vinegar/formic acid → flattened hair cuticle → better combing efficiency (does not dissolve/loosen nits) Prevention ▪ Proper hygiene
Chapter 69 Ectoparasites ▪ Household ▫ Housemates: examination ▫ Bedmates: prophylactic treatment ▫ Household cleaning: washing > 54°C/130°F; unwashable material → place in sealed plastic bag for two weeks ▪ School ▫ No nit policy (infected children stay home), education, screening during outbreaks SARCOPTES SCABIEI (SCABIES) PATHOLOGY & CAUSES ▪ Sarcoptes scabiei mite infection ▫ Elicits strong immune response ▫ Nocturnal pruritus Mite infection ▪ (Phylum) mite → (class) arachnida → (subclass) acari → (order) astigmata → (family) sarcoptidae ▫ Usually obligate human parasite → vars hominis ▫ Sometimes animal mange mites can infest PATHOLOGY Mite transfer ▪ Direct skin-to-skin contact for 15–20 minutes ▪ Average infested individual carries 5–12 mites ▫ Crusted scabies individuals: > 1000 mites can be shed (transmission through objects more likely) Type IV hypersensitivity reaction ▪ House dust mite cross reactivity ▪ Infestation → ↑ IL-6, vascular epithelial growth factor (VEGF) →TH1-cell activation → IL-2 release → lymphocyte proliferation, differentiation RISK FACTORS ▪ Overcrowding (including long-term care facilities, prisons), poor hygiene/nutrition, homelessness, dementia, sexual contact COMPLICATIONS ▪ Infestation → secondary staphylococcal infection ▫ Low-income countries (mostly) ▫ Impetigo → chronic kidney disease ▫ Ecthyma, paronychia, furunculosis Crusted scabies ▪ AKA Norwegian scabies ▪ Infection commonly scalp, hands, feet → diffuse spread over entire body ▪ Occurs in compromised cellular immunity setting ▫ Acquired immunodeficiency syndrome (AIDS) ▫ Human lymphocytic virus type 1 (HTLV1) ▫ Leprosy ▫ Lymphoma ▫ Long-term topical corticosteroid use ▪ Risk factors: age, Down syndrome ▪ Complications: fissional lesions develop → bacterial entryway → infection ▫ Sepsis, poststreptococcal glomerulonephritis OSMOSIS.ORG 377
SIGNS & SYMPTOMS Classic scabies ▪ Intense, intractable, generalized pruritus ▪ Nodules, pustules at most intense pruritus sites ▪ Common areas → intertriginous spaces ▫ Anterior axillary folds, webs of fingers, volar aspect of hand/wrist, beltline, penis, areolar region (biologically-female individuals) Dermatologic examination ▪ Serpiginous keratotic lines (1–4mm) → burrow marks ▫ Often with vesicle on end (housing mite) Nodular scabies ▪ Hypersensitivity reactions → large, persistent, intensely pruritic 5–6mm nodules ▫ Commonly groin, buttock, axillary folds Crusted scabies ▪ Poorly defined, erythematous patches → scale ▫ Untreated → entire integumental spread → warty appearance (especially over bony prominences); lesions crust, fissure develop → malodorous; nail involvement → thickened, dystrophic, discolored DIAGNOSIS LAB RESULTS Microscopy ▪ Confirmatory scraping: fluorescein stain → highlights fecal material, ova fragments ▫ Epithelial milieu (eosinophils, lymphocytes, histiocytes) ▫ Crusted scabies: mate capture more likely due to disease burden Polymerase chain reaction assays ▪ S. scabiei DNA polymerase OTHER DIAGNOSTICS History ▪ Close contact commonly present with concurrent symptoms ▪ Infected individual contact history (may be many weeks prior) 378 OSMOSIS.ORG Figure 69.1 A high-magnification photograph of a single mite burrow in the skin of an individual with scabies. The mite is at the end of the burrow at the top right of the image. TREATMENT MEDICATIONS Classic scabies ▪ Permethrin (5%) → synthetic neurotoxin → Na+ channel blocker → paralysis → death ▪ Precipitated sulfur (6%, 10%) in petroleum ▪ Benzyl benzoate (10%, 25%) ▫ Adverse reactions: allergic dermatitis ▫ Contraindications: pregnancy/lactation (neurotoxicity); children < two years old ▪ Oral ivermectin ▫ One dose (200mcg/kg) repeated in 7–10 days Nodular scabies ▪ Topical steroids ▪ Intralesional steroid injection Crusted scabies ▪ Topical, systemic treatment required ▪ Oral ivermectin, topical permethrin (5%)/ benzyl benzoate (5%) ▫ Two week oral regimen, topical therapy
Chapter 69 Ectoparasites persisting after that twice weekly until cure ▫ Treatment cure → active lesion resolution, nocturnal pruritus absence for one week OTHER INTERVENTIONS ▪ Isolation for infected ▪ Nail clipping ▫ +/- brushing with scabicidal agent ▪ Thorough personal, household material laundering Prevention ▪ Monosulfiram soap in communities with ↑ ↑ incidence OSMOSIS.ORG 379

Osmosis High-Yield Notes

This Osmosis High-Yield Note provides an overview of Ectoparasites essentials. All Osmosis Notes are clearly laid-out and contain striking images, tables, and diagrams to help visual learners understand complex topics quickly and efficiently. Find more information about Ectoparasites by visiting the associated Learn Page.