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Infestations Flashcards

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Dermatology Board Prep flashcards
1
Q

How long can scabies live off a human

A

Normal - 3 days

Norwegian - 7 days

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2
Q

Cause of scabies

A

Sarcoptes scabiei var hominis

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3
Q

Size of scabies

A

0.35 X 0.3 mm

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4
Q

Life cycle of a scabies mite

A

30 days

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5
Q

How often does a scabies mite lay eggs

A

every 3 days

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6
Q

Talk through the life cycle

A

15 minutes of copulation once per female mite lifetime
Female takes 1-2 days to burrow and lay eggs
Egg takes 2-2.5 days to become Larva
Larva look like an adult but have 6 legs as opposed to 8
The larva spends 1 day on the skin then burrows back into the skin
The larva then takes 3-4 days to become a protonymph
Then 3 days to become a tritonymph
Then 2-3 days to become an adult scabies mite

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7
Q

Incubation period of scabies

A

Initially 2-6 weeks before the immune system becomes sensitized
Recurrent - 24-48 hours

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8
Q

What is a burrow

A

The tunnel that the female mite excavates while laying eggs

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9
Q

A/E from permethrin and what is it

A

ACD in those with formaldehyde sensitivity
<2 months of age
Cat B

It is a synthetic pyrethroid

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10
Q

A/E from lindane lotion 1%

A

CNS toxicity - particularly if <50 kg, elderly, crusted scabies, hx of seizures
Not for infants, children, breastfeeding mothers
Category C for pregnancy
Not that good

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11
Q

A/E from crotamition lotion 10%

A

ICD
Not that good
Cat C

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12
Q

How would you use sulfur ointment

A

5-10%

Topically overnight for 3 days in a row`

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13
Q

MOA of permethrin

A

inhibits sodium transport in arthropod neurons

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14
Q

A/E of topical sulfur

A

Messy, malodorous, irritating to skin, stains clothing

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15
Q

MOA of ivermectin

A

Blocks transmission across nerve synapses that utilize glutamate or GABA, causing paralysis of peripheral motor function in insects and acarines

Our BBB prevents CNS penetration, but don’t recommend in infant <15 kg

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16
Q

What to do if subungual disease

A

Need topical scabicide as well as a systemic because systemic won’t penetrate thickened keratotic debris

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17
Q

Head lice cause

A

Pediculus capitis

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18
Q

Head lice size

A

2-3 mm

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19
Q

Head lice life cycle and feeding pattern

A

30 days

Feeds every 6 hours

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20
Q

How long can head lice live away from the scalp

A

No more than 36 hours usually

But if hot and humid then can survive up to 10 days

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21
Q

How many eggs with a head lice lay in their time

A

5-10 eggs

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22
Q

Where do head lice lay their eggs

A

Near the scalp for warmth, and in a cool environment if >1 cm away from the scalp then is unhatched
But if its a warm environment, then it might 15 cm away from the scalp, and in the nape of the neck

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23
Q

What is the incubation period for head lice

A

2-6 weeks initially (delayed immunologic response to components of lice saliva or excreta)
Second time onwards 24-48 hours

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24
Q

What do the head lice eggs look like

A

Viable: tan to brown
Hatched: clear to white

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25
Q

What has been touted as helpful for head lice but not recommended

A

Petroleum jelly, oils, mayonnaise –> slows the movement down but doesn’t get rid of

Bactrim given may improve efficacy but no recommended

26
Q

What is pyrethrin from

A

Natural extract from Chrysanthemum

Can cause wheezing and dyspnoea in those who are allergic to it

27
Q

What can you add to pyrethrin to assist with efficacy in head lice

A

Piperonyl butoxide - slows the biotransformations of pyrethrins by partially inhibiting the insects CyP450 enzymes

28
Q

How do head lice become resistant to permethrin

A

Point mutations in gene encoding the alpha subunit of the insects voltage sensitive sodium channels

29
Q

Would you use lindane for head lice

A

No its not that efficacious, plus has black box warnings for CNS toxicity

30
Q

What are 5 products for head lice that have good efficacy and how would you use

A

Benzyl alcohol 5%- apply to dry hair for 10 minutes
Malathion 0.5%- 8-12 hours to dry hair
Topical 0.5% or systemic ivermectin - topical 10 minutes, or 200-400 microg/kg
Spinosad 0.9%- topical for 10 minutes to dry hair
Dimethicone 4%- topical for 15 minutes or over night

31
Q

How does malathion work and any side effects

A

Cholinesterase inhibitor

Has a flammable alcohol base, so can cause burning, stinging at sites of eroded skin

32
Q

How does carbaryl work

A

Also is a cholinesterase inhibitor, not as good as malathion and possible carcinogen

33
Q

How does benzyl alcohol work with head lice

A

Asphyxiation by preventing lice from closing their respiratory spiracles

34
Q

How does dimethicone work for head lice

A

Silicone oil- suffocates the lice or blocks their ability to excrete water

35
Q

How does spinosad work for head lice

A

0.9% topical suspension
Used for >4 years
Fermentation produce of Saccharopolyspora spinosa - induces muscle spasms and paralysis in lice when applied topically

36
Q

Describe life cycle of head lice

A

Egg can take 10-12 days to become first instar/nymph, then 3-4 day molt to second, then 3-4 day to third, then 3-4 days to adult louse
Adult louse must take blood meal before copulating (male), then copulate and 1-2 days later lay eggs
Eggs are 0.8 mm

37
Q

What is the cause of pubic lice

A

Pthirus pubis

38
Q

What do crab lice look like

A

1 mm in length, tiny crabs

Serrated edges on first claw so they can ambulate the body surface

39
Q

How long do crab lice last off the body

A

36 hours

Eggs are viable for 10 days

40
Q

What clinically do you expect to see in pubic lice

A
  1. Involvement of more than one area common - scalp, eyebrows, eyelashes, peri-anal, etc
  2. Macula caerula: gray to blue macules on the trunk and thighs, from break down of bilirubin to biliverdin by enzymes in the lice’s saliva
  3. Infectious - bacterial, can have lymphadenopathy
  4. Nits at base of shafts, peri-follicular erythema, excoriations, eyelashes may look like they have mascara (faeces)
41
Q

Best treatment for pubic lice

A

Permethrin 1% for 10 minutes
Permethrin 5% for 8-12 hours - better
Lindane shampoo 1% - CNS toxicity, for 4 minutes to dry hair
Ivermectin 250 microg/kg - excellent, but CNS toxicity

42
Q

Cause of body lice

A

Pediculus humanis var corporis

43
Q

What can body lice help transmit

A
  1. Epidemic typhus (Rickettsia prowazekii)
  2. Relapsing fever (Borellia)
  3. Bartonella quintana: trench fever, bacillary angiomatosis, endocarditis
44
Q

Body lice transmission

A

Inoculation of faeces into the skin via scratching or inhalation of dry, powdery louse faeces from infested bedding or clothing

45
Q

Where will you find body lice

A

On the seams of clothing - neck, axillae, waistline

46
Q

Body lice treatment

A

Discard and incinerate infected things
If not, fumigation adn washing in >55 degree heat
Stop exposure for > 2 weeks

47
Q

Cause of tungiasis

A

Tungas penetrans

48
Q

Where is tungiasis endemic

A

Central and South America, Carribean, Africa, India, pakistan

49
Q

What does tungas penetrans look like

A

Wingless fly, 1 mm in size, and likes warm, dry soil

Requires occasional blood meal

50
Q

How does tungiasis develop

A

Female flee burrows into the dermis of skin on the feet, and then undergo abdominal hypertrophy growing to 1 cm in diameter
It protrudes its rear cone through a central punctum, and whether or not gets fertilized it emits over a hundred eggs within 3 weeks
After expelling the eggs, the female dies

51
Q

What does tungiasis look like

A

On the bottom of feet
Small black dot, then evolves into a whitish papule, then a large nodule that looks like a watch glass with a clearly demarcated white halo surrounding the black central punctum
Peripheral zone of erythema
When flea dies, black crust covers the involiting lesion

52
Q

Complications from tungiasis

A 
Secondary infection
Lymphangitis
Tetanus
Gangrene
Amputation
53
Q

List of tungiasis treatments

A

Spontaneous recovery can occur
Removal of flea: sterile needle, curette, surgical excision
Covering hole with dimethicone or liquid paraffin - prevents flea growth and expedites removal
Antibiotics
Tetanus prophylaxis
Topica: ivermectin, metrifonate, thiabendazole
Prevention: enclosed shoes
Insect repellant: coconut and jojoba oils

54
Q

Where do you find myasis

A

Hot tropical places in the summer

55
Q

What are the most common causes of myasis?

A

Diptera athropods: 2 winged fly

  1. Human botfly - dermatobia hominis
  2. Tumbu fly - Cordylovia anthropophaga

Then wound:

  1. Screw worm - cochliomyia hominivorax in US
  2. Chrysomya bezziana in Australia, Africa Asia

Then creeping:

  1. Hypoderma bovis - cattle
  2. Gasterophilus intestinalis - horses
56
Q

Lifecycle of the human botfly (dermatobia hominis)

A

Adult botfly emerges from soil
Gravid female seizes blood sucking insect and oviposits 10-50 eggs
The eggs are then hatched when in an elevated temperature and rapidly penetrate the skin
First stage larva
Second stage - makes it hard ti dislodge due to anatomical structure
Third stage larva - emerges in 5-10 weeks and falls to teh ground to pupate in the soil
4-11 weeks later a botfly emerges

57
Q

How does C anthropophaga deposit its eggs?

A

Onto moist clothing and soiled blankets in the sand

Larva can live 15 days without feeding, but once hits skin it infests and matures

58
Q

Clinical myasis

A
  1. Furuncular
    - Tumbu fly: trunk, thighs, buttocks (clothing)
    - Botfly: scalp, face, forearms, legs (more exposed)
    - Papule after 24 hours, then nodule 1-3 cm in size with central punctum
    - painful, tender, sensation of movement, purulent
  2. Wound
    - can infest around orifices of head and may burrow into brain tissue (C hominivorax)
    - nasal cavity, sinuses and scalp associated wtih serious sequelae too
    - can be a portal of entry from Clostridium tetani
  3. Creeping or migratory
    - looks like cutaneous larva migrans, but slower and persists for longer, and are larger than helminth larvae
59
Q

Myasis pathology

A

Lots of inflammation: neuts, eos, mast cells, giant cells, lymphocytes, plasma cells
Larvae in cross-section

60
Q

Myasis treatment options

A
  1. Do not forcibly remoed as its shape will prevent this
  2. Surgical debridement under anaesthetic - curative –> not required unless patient asks, as will come off in 2 weeks anyway
  3. Suffocate with occlusion - petroleum –> then will come up for air over a few hours and then capture
  4. LN2
  5. Chloroform
  6. Insecticides
  7. Ethyl chloride sprays
  8. Inject lidocaine to base of cavity
  9. Wound: debride and irrigate
  10. Oral ivermectin - particularly helpful for oral and orbital involvement
  11. Tetanus vaccination

Derm (57 decks)

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