Infestations

Question 1

How long can scabies live off a human

Answer 1

Normal - 3 days

Norwegian - 7 days

Question 2

Cause of scabies

Answer 2

Sarcoptes scabiei var hominis

Question 3

Size of scabies

Answer 3

0.35 X 0.3 mm

Question 4

Life cycle of a scabies mite

Answer 4

30 days

Question 5

How often does a scabies mite lay eggs

Answer 5

every 3 days

Question 6

Talk through the life cycle

Answer 6

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

Question 7

Incubation period of scabies

Answer 7

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

Question 8

What is a burrow

Answer 8

The tunnel that the female mite excavates while laying eggs

Question 9

A/E from permethrin and what is it

Answer 9

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

It is a synthetic pyrethroid

Question 10

A/E from lindane lotion 1%

Answer 10

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

Question 11

A/E from crotamition lotion 10%

Answer 11

ICD
Not that good
Cat C

Question 12

How would you use sulfur ointment

Answer 12

5-10%

Topically overnight for 3 days in a row`

Question 13

MOA of permethrin

Answer 13

inhibits sodium transport in arthropod neurons

Question 14

A/E of topical sulfur

Answer 14

Messy, malodorous, irritating to skin, stains clothing

Question 15

MOA of ivermectin

Answer 15

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

Question 16

What to do if subungual disease

Answer 16

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

Question 17

Head lice cause

Answer 17

Pediculus capitis

Question 18

Head lice size

Answer 18

2-3 mm

Question 19

Head lice life cycle and feeding pattern

Answer 19

30 days

Feeds every 6 hours

Question 20

How long can head lice live away from the scalp

Answer 20

No more than 36 hours usually

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

Question 21

How many eggs with a head lice lay in their time

Answer 21

5-10 eggs

Question 22

Where do head lice lay their eggs

Answer 22

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

Question 23

What is the incubation period for head lice

Answer 23

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

Question 24

What do the head lice eggs look like

Answer 24

Viable: tan to brown
Hatched: clear to white

Question 25

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

Answer 25

Petroleum jelly, oils, mayonnaise --> slows the movement down but doesn't get rid of Bactrim given may improve efficacy but no recommended

Question 26

What is pyrethrin from

Answer 26

Natural extract from Chrysanthemum | Can cause wheezing and dyspnoea in those who are allergic to it

Question 27

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

Answer 27

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

Question 28

How do head lice become resistant to permethrin

Answer 28

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

Question 29

Would you use lindane for head lice

Answer 29

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

Question 30

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

Answer 30

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

Question 31

How does malathion work and any side effects

Answer 31

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

Question 32

How does carbaryl work

Answer 32

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

Question 33

How does benzyl alcohol work with head lice

Answer 33

Asphyxiation by preventing lice from closing their respiratory spiracles

Question 34

How does dimethicone work for head lice

Answer 34

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

Question 35

How does spinosad work for head lice

Answer 35

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

Question 36

Describe life cycle of head lice

Answer 36

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

Question 37

What is the cause of pubic lice

Answer 37

Pthirus pubis

Question 38

What do crab lice look like

Answer 38

1 mm in length, tiny crabs | Serrated edges on first claw so they can ambulate the body surface

Question 39

How long do crab lice last off the body

Answer 39

36 hours | Eggs are viable for 10 days

Question 40

What clinically do you expect to see in pubic lice

Answer 40

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)

Question 41

Best treatment for pubic lice

Answer 41

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

Question 42

Cause of body lice

Answer 42

Pediculus humanis var corporis

Question 43

What can body lice help transmit

Answer 43

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

Question 44

Body lice transmission

Answer 44

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

Question 45

Where will you find body lice

Answer 45

On the seams of clothing - neck, axillae, waistline

Question 46

Body lice treatment

Answer 46

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

Question 47

Cause of tungiasis

Answer 47

Tungas penetrans

Question 48

Where is tungiasis endemic

Answer 48

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

Question 49

What does tungas penetrans look like

Answer 49

Wingless fly, 1 mm in size, and likes warm, dry soil | Requires occasional blood meal

Question 50

How does tungiasis develop

Answer 50

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

Question 51

What does tungiasis look like

Answer 51

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

Question 52

Complications from tungiasis

Answer 52

``` Secondary infection Lymphangitis Tetanus Gangrene Amputation ```

Question 53

List of tungiasis treatments

Answer 53

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

Question 54

Where do you find myasis

Answer 54

Hot tropical places in the summer

Question 55

What are the most common causes of myasis?

Answer 55

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

Question 56

Lifecycle of the human botfly (dermatobia hominis)

Answer 56

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

Question 57

How does C anthropophaga deposit its eggs?

Answer 57

Onto moist clothing and soiled blankets in the sand | Larva can live 15 days without feeding, but once hits skin it infests and matures

Question 58

Clinical myasis

Answer 58

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

Question 59

Myasis pathology

Answer 59

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

Question 60

Myasis treatment options

Answer 60

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