Parasites, bites, and infestations

Question 1

Types of arthropods

Answer 1

• Insecta (3 pairs of legs): lice, flies, mosquitos, fleas, bedbugs, bees
• Arachnida (4 pairs of legs): spiders, mites, ticks

Question 2

Pediculosis (lice)

Answer 2

• Pediculosis humanus capitis (head lice): pruritus of scalp, linear excoriation at the periphery of the hair
• Most common in children
• Pediculosis corporis (body lice): from contaminated clothing or bedding
• Pruritus and excoriations of trunk and neck
• Lice in clothing, not hair
• Vector for typhus fever
• Pediculosis pubis (crabs): spread as STD
• Dx: identification of adult lice (nit)
• Rx: permethrin, ivermectin, lindane (associated w/ seizures)
• Kill fomites (bedding, clothes, ect) by washing in hot water

Question 3

Papular uticaria

Answer 3

• Allergic hypersensitivity rxn to arthropod bites (flea, bed bugs, mosquitos, mites)
• Pruitic urticarial papules (hives), which are often excoriated and may be secondarily infected
• Fleas are vectors for many diseases

Question 4

Bed bugs

Answer 4

• Reddish brown blood-sucking insects
• Inject anticoagulant and anesthetic-containing saliva and feed at night
• Bites often noted in groups of 3
• Rx: topical steroids and oral antihistamines
• Prevention: insecticides, insect repellent

Question 5

Mosquitos

Answer 5

• Responsible for transmission of more diseases than any other arthropod
• Attracted to human skin
• Prevention: topical repellents

Question 6

Allergic reactions to insect stings

Answer 6

• Major Ag: melittin, phospholipase-A
• Liberate acute inflammatory mediators
• Signs: itch and pain (normal), itch/pain and swelling (severe), urticaria/bronchospasm/hypotension/shock (anaphylactic)
• Toxic reactions (>10 stings): headache, fever, GI problems
• Rx: antihistamines, topical or oral steroids. For anaphylaxis use subcutaneous epinephrine

Question 7

Scabies

Answer 7

• Caused by mites, transmitted by skin-skin contact, sex
• Presentation: intense itching, often in btwn fingers, flexor surfaces of wrist, elbows, axillae, belt line, feet, scrotum, areolae
• Burrow is usually 2-5 mm long, slightly elevated, and pinkish-white
• Dx: identify mite, eggs, or feces
• Rx: for all family members, use permethrin ivermectin, sulfur in petrolatum. Also wash beds, clothes, ect

Question 8

Types of scabies

Answer 8

• Scabies incognito: atypical presentation b/c use of steroids
• Nodular scabies: papules rarely contain mites, usually do to hypersensitivity rxn
• In children usually in face, soles, palms, scalp
• Crusted scabies: hyperkeratotic and crusted over large areas
• Complications: secondary bacterial infections

Question 9

Other mite infestations

Answer 9

• Demodex is etiologic agent of rosacea
• Trombiculi mites (chiggers), mainly on lower extremities
• Many others
• Manifestations: papular urticaria
• Rx: topical antipruritics, anesthetics, corticosteroids

Question 10

Ticks

Answer 10

• Hard (ixodidae) and soft (argasidae) ticks
• Have 4 stage life cycle (egg, larva, nymph, adult)
• Ixodes (deer tick) transmits borrelia bugdorferi (lyme disease)
• Lyme disease symptoms: ECM (erythema chronic migrans), and erythematous annular patch that expands from site of bite. Leave central clearing (target-like)
• Rx: tetracyclines, fluoroquinolones, amoxicillin, erythromycin
• Prevention most important

Question 11

Brown recluse

Answer 11

• Small brown spider (violin case on body)
• Venom contains 9 protein fractions (one is sphingomyelinase D)
• Bite is painless, can range from mild to urticarial rxn to full-thickness skin necrosis
• Bites over 2 cm can induce hemolysis
• Rx: ice, elevation, debridement, topical antibios, prednisone

Question 12

Black widow

Answer 12

• Venom contains neurotoxin alpha-latrotoxin, which causes systemic symptoms after 1-8 hrs
• Symptoms: abdominal cramps, chest pain
• Death in 1% of cases
• Rx: antivenom for severe cases, calcium gluconate, muscle relaxants

Question 13

Cutaneous myiasis

Answer 13

• Botfly larvae (maggots) penetrate skin (furuncular myiasis) or are deposited into open wounds
• Rx: occluding lesion w/ petrolatum

Question 14

Cutaneous larva migrans

Answer 14

• Creeping eruption, due to hookworm
• Cause erythematous, serpiginous pruritic, cutaneous eruption
• Common on feet, interdigits, butt, hands, and knees
• Rx: antihelmintics (topical thiabendazole)