Infestations

Question 1

What is scabies?

Answer 1

A pruritic condition caused by infestations with the host specific mite - Sarcoptes Scabei var hominis

Sarcoptes Scabei Var canis (and other animal infestations) are NOT a source of infestation for humans. They can produce bite reactions.

Question 2

What is the name of the mite that causes scabies?

Answer 2

Sarcoptes Scabei var Hominis - in humans.

Question 3

What are the key clinical features of scabies?

Answer 3

Intense pruritis, symmetrical cutaneous lesions, erythematous papules, excoriations, vesicles, indurated nodules, eczematous dermatitis, acral vesicopustules, burrows.

Burrows are wavy, thread-like, gray-white and 1-10mm in length.

Question 4

How is scabies transmitted?

Answer 4

Directly - via close personal contact, indirectly - via fomites.

Question 5

What does the scabies mite look like?

Answer 5

An eight-legged mite.

Question 6

Describe the scabies life cycle.

Answer 6

30 days, happens within the epidermis. Female copulation occurs ONCE per adult female lifetime. Each female mite lays 2-3 eggs per day. An egg takes ten days to mature.

Question 7

Who does scabies affect?

Answer 7

Children > Adults, sexually active individuals.

Question 8

Who does crusted scabies affect?

Answer 8

Patients with a compromised immune system, including those with HIV, HTLV-1, solid organ transplant, decreased sensory function, and inability to scratch (infants).

Question 9

How many mites are on an infected person?

Answer 9

Varies greatly, normally fewer than 100 (no more than 10-15); crusted scabies = thousands.

Question 10

How long can a scabies mite live off a human host?

Answer 10

~ 3 days, unless crusted scabies (7 days - as feed off sloughed skin).

Question 11

How long after infection does a person become symptomatic?

Answer 11

Takes 2-6 weeks for the host to become sensitized to the mite or its byproducts; within 24-48 hours for subsequent infections.

Question 12

What are some complications of scabies?

Answer 12

Secondary skin infection (Staph Aureus, Strep Pyogenes), post-strep glomerulonephritis, peripheral eosinophilia, sleep disturbance, psychological distress.

Question 13

What investigations would you do for scabies?

Answer 13

Often a clinical diagnosis, light microscopy examination of mineral oil preparations of skin scrapings, biopsy will only be diagnostic if mites are biopsied.

Question 14

What are the techniques of performing light microscopy?

Answer 14

Skin scrapings - mineral oil preparation, transparent adhesive tape applied to infestation areas of skin.

Question 15

What are the dermoscopy features of scabies?

Answer 15

Dark, triangular shape representing the head of the mite within a burrow (‘delta wing’ sign) or jet with contrail.

Question 16

What are the histological features of scabies?

Answer 16

A patchy to diffuse infiltrate in the reticular dermis, prominent eosinophils, lymphocytes, histiocytes, pink ‘pigtail like structures’ attached to the stratum corneum.

Question 17

What is a differential diagnosis for scabies?

Answer 17

Insect bite reaction, papular eczema, ID reactions, atopic dermatitis, allergic contact dermatitis, dermatitis herpetiformis, bullous pemphigoid, acropustolosis of infancy, eosinophilic folliculitis.

Question 18

List 6 topical treatments for scabies and one oral treatment.

Answer 18

• Permethrin 5% cream
• Sulfur ointment (5-10%)
• Benzyl benzoate lotion or emulsion (10-25%)
• Spinosad Suspension (0.9%)
• Crotamiton lotion
• Lindane lotion
• Oral: Ivermectin 200 mcg/kg.

Question 19

What treatments are safe in pregnancy for scabies treatment?

Answer 19

Permethrin, Spinosad Suspension (0.9%), Sulfur ointment.

Question 20

How does Permethrin work?

Answer 20

Inhibits sodium transport in the arthropod neurons, causing paralysis.

Apply to the neck down with special consideration to the fingers, web spaces, feet, umbilicus. Leave on overnight.

Question 21

How does Ivermectin work?

Answer 21

Blocks nerve synapses - causes mite paralysis.

Dose on day 0 and on day 7.

Question 22

Is Ivermectin safe in pregnancy or breastfeeding?

Answer 22

No.

Question 23

What are the management options for scabies?

Answer 23

• First line: permethrin 5% cream (category B in pregnancy) and oral ivermectin 200 mcg/kg (avoid in pregnancy)
• Ivermectin for large outbreaks, nodular scabies, crusted scabies.
• Other treatments: benzyl benzoate, crotamiton, lindane, malathion, sulfur in petrolatum.

Question 24

What is the method for applying Permethrin cream?

Answer 24

Massage thoroughly into skin from the neck down, including areas under fingernails and toenails. Treat every inch of skin.

Special attention to interdigital spaces, intergluteal cleft, umbilicus, and subungual areas.

Question 25

How to prevent re-infection of scabies?

Answer 25

* Examine other family members * Treat household and close personal contacts * Wash clothing and linen used by the infested person. * Prevent direct contact for 24 hours after treatment.

Question 26

What can be used for post-scabetic itch?

Answer 26

* Moderate potency topical steroids for 3-4 weeks * Antihistamines * Emollient use and soap avoidance.

Question 27

What is another name for head lice?

Answer 27

Pediculosis Capitus

Question 28

What do head lice look like?

Answer 28

6 legs, wingless insects

Question 29

head lice is less common in African Americans

Answer 29

True - they cannot properly position themselves to lay eggs on coarse curly hair

Question 30

What organism causes head lice?

Answer 30

Pediculus capitus

Question 31

How long do head lice live?

Answer 31

Obligate human parasites - feed off human blood every 4 - 6 hours. Will live for 30 days on the scalp.

Question 32

How many eggs do head lice lay per day?

Answer 32

5 to 10 eggs a day.

Question 33

How long can head lice live away from the host?

Answer 33

36 hours ## Footnote The nits (eggs) can survive and hatch 10 days away from a host.

Question 34

How are lice transmitted?

Answer 34

Fomites or direct contact ## Footnote It takes 2 - 6 weeks for pruritis / symptoms after infection (first) and 24 - 28 hours for subsequent infection.

Question 35

What are the clinical features of head lice?

Answer 35

Pruritis, Excoriations, Erythema, Scale, Visible eggs (tan to brown), Hatched eggs (white), Fever, Lymphadenopathy

Question 36

What are the complications of head lice?

Answer 36

Secondary bacterial infection (Strep pyogenes, Staph Aureus, Possible Bartonella recurrentis, Acinetobacter), Sleep disturbance

Question 37

What are the treatments for head lice?

Answer 37

Malathion lotion 0.5%, Oral ivermectin, Ivermectin lotion 0.5%, Dimethicone liquid 4 - 100%, Pyrethrine 0.33%, Permethrin cream or lotion 1%, Spinosad suspension, Benzyl alcohol lotion, Abametapir lotion

Question 38

Which treatments are ovicidal?

Answer 38

TOPICAL (not oral) ivermectin

Question 39

What organism causes crab lice?

Answer 39

Pthirus pubis

Question 40

How long can a crab lice live away from the host?

Answer 40

36 hours

Question 41

How long do crab lice live for?

Answer 41

10 days

Question 42

How does pthirus pubis infection present?

Answer 42

Pruritis ## Footnote Typically pubic hair, can be anywhere

Question 43

What are the symptoms of pthirus pubis infection?

Answer 43

Nits, Erythema, Scale, Excoriations

Question 44

How are crab lice treated?

Answer 44

Permethrin 1% or 5%, Pyrethrin products

Question 45

How does the scabies mite stay within the stratum corneum and avoid deeper immune detection?

Answer 45

It avoids immune detection by: Physical location: It never penetrates into the dermis, where the majority of immune surveillance (Langerhans cells, dendritic cells, capillary access) is more robust. Slow burrowing: It moves horizontally, not vertically, creating serpiginous tunnels that don’t pierce through to deeper immune-rich layers. Small antigen burden: Early in infestation, the number of mites is low (10–15), which delays antigen presentation.

Question 46

How does permethrin work at the ion channel level?

Answer 46

Permethrin is a synthetic pyrethroid that binds to voltage-gated sodium channels in the neurons of arthropods (mites, lice). It prevents the closure of sodium channels, leading to prolonged depolarization of the nerve membrane. This causes repetitive nerve firing, followed by neuronal paralysis and death of the mite.

Question 47

What distinguishes crusted scabies immunologically and histologically from classic scabies?

Answer 47

Crusted scabies (formerly Norwegian scabies) is an extreme form seen in immunocompromised individuals (HIV, elderly, HTLV-1, leprosy, paraplegia). Here's how it differs: Immunologically: Defective Th1/Th2 responses: Patients fail to mount an effective T cell–mediated immune response. This allows mites to proliferate unchecked, reaching numbers in the millions (vs. 10–15 in classic scabies). Pruritus may be minimal or absent, since there's no effective immune activation. Histologically: Massive hyperkeratosis (thickened stratum corneum) Pachydermatous plaques Thousands of mites visible in the epidermis (vs. rare in classic cases) Eosinophil-rich infiltrate in dermis may still be seen

Question 48

Why does scabies usually spare the face in adults, but involve it in infants?

Answer 48

In adults, the stratum corneum on the face is thinner, and sebaceous gland secretions (sebum) create an unfavorable environment for the mites. In infants, the entire skin is thinner, more permeable, and lacks mature sebaceous gland activity, so mites can more easily colonize areas like the face and scalp.

Question 49

What is a burrow

Answer 49

a wavy, thread-like, gray-white tunnel ~1–10 mm long. Most common sites: Interdigital web spaces, flexor surfaces of the wrists, anterior axillary folds, umbilicus, buttocks, male genitals, female areolae

Question 50

Which populations are more prone to crusted scabies, and why are they considered hypercontagious?

Answer 50

Populations at risk: HIV-positive individuals HTLV-1 patients Elderly Solid organ transplant recipients Neurologically impaired (e.g., leprosy, paraplegia) Crusted scabies can contain millions of mites, and patients shed live mites into their environment (e.g., sheets, floors, curtains), making them hypercontagious.

Question 51

How can infants and immunocompromised patients present differently from immunocompetent adults with scabies?

Answer 51

Infants: - Scalp, face, neck, palms, soles involved — due to immature skin barrier and lack of sebum - May show acral vesiculopustules Immunosuppressed: - Often develop crusted scabies - Minimal or absent pruritus - Massive mite burden → extensive keratotic plaques

Question 52

What technique is most definitive for diagnosing scabies under the microscope, and what are you looking for specifically?

Answer 52

Procedure: Skin scraping with mineral oil or KOH Examined under light microscopy Looking for: Mites Eggs Fecal pellets (scybala)