Infestations Flashcards
How long can scabies live off a human
Normal - 3 days
Norwegian - 7 days
Cause of scabies
Sarcoptes scabiei var hominis
Size of scabies
0.35 X 0.3 mm
Life cycle of a scabies mite
30 days
How often does a scabies mite lay eggs
every 3 days
Talk through the life cycle
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
Incubation period of scabies
Initially 2-6 weeks before the immune system becomes sensitized
Recurrent - 24-48 hours
What is a burrow
The tunnel that the female mite excavates while laying eggs
A/E from permethrin and what is it
ACD in those with formaldehyde sensitivity
<2 months of age
Cat B
It is a synthetic pyrethroid
A/E from lindane lotion 1%
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
A/E from crotamition lotion 10%
ICD
Not that good
Cat C
How would you use sulfur ointment
5-10%
Topically overnight for 3 days in a row`
MOA of permethrin
inhibits sodium transport in arthropod neurons
A/E of topical sulfur
Messy, malodorous, irritating to skin, stains clothing
MOA of ivermectin
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
What to do if subungual disease
Need topical scabicide as well as a systemic because systemic won’t penetrate thickened keratotic debris
Head lice cause
Pediculus capitis
Head lice size
2-3 mm
Head lice life cycle and feeding pattern
30 days
Feeds every 6 hours
How long can head lice live away from the scalp
No more than 36 hours usually
But if hot and humid then can survive up to 10 days
How many eggs with a head lice lay in their time
5-10 eggs
Where do head lice lay their eggs
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
What is the incubation period for head lice
2-6 weeks initially (delayed immunologic response to components of lice saliva or excreta)
Second time onwards 24-48 hours
What do the head lice eggs look like
Viable: tan to brown
Hatched: clear to white
What has been touted as helpful for head lice but not recommended
Petroleum jelly, oils, mayonnaise –> slows the movement down but doesn’t get rid of
Bactrim given may improve efficacy but no recommended
What is pyrethrin from
Natural extract from Chrysanthemum
Can cause wheezing and dyspnoea in those who are allergic to it
What can you add to pyrethrin to assist with efficacy in head lice
Piperonyl butoxide - slows the biotransformations of pyrethrins by partially inhibiting the insects CyP450 enzymes
How do head lice become resistant to permethrin
Point mutations in gene encoding the alpha subunit of the insects voltage sensitive sodium channels
Would you use lindane for head lice
No its not that efficacious, plus has black box warnings for CNS toxicity
What are 5 products for head lice that have good efficacy and how would you use
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
How does malathion work and any side effects
Cholinesterase inhibitor
Has a flammable alcohol base, so can cause burning, stinging at sites of eroded skin
How does carbaryl work
Also is a cholinesterase inhibitor, not as good as malathion and possible carcinogen
How does benzyl alcohol work with head lice
Asphyxiation by preventing lice from closing their respiratory spiracles
How does dimethicone work for head lice
Silicone oil- suffocates the lice or blocks their ability to excrete water
How does spinosad work for head lice
0.9% topical suspension
Used for >4 years
Fermentation produce of Saccharopolyspora spinosa - induces muscle spasms and paralysis in lice when applied topically
Describe life cycle of head lice
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
What is the cause of pubic lice
Pthirus pubis
What do crab lice look like
1 mm in length, tiny crabs
Serrated edges on first claw so they can ambulate the body surface
How long do crab lice last off the body
36 hours
Eggs are viable for 10 days
What clinically do you expect to see in pubic lice
- Involvement of more than one area common - scalp, eyebrows, eyelashes, peri-anal, etc
- 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
- Infectious - bacterial, can have lymphadenopathy
- Nits at base of shafts, peri-follicular erythema, excoriations, eyelashes may look like they have mascara (faeces)
Best treatment for pubic lice
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
Cause of body lice
Pediculus humanis var corporis
What can body lice help transmit
- Epidemic typhus (Rickettsia prowazekii)
- Relapsing fever (Borellia)
- Bartonella quintana: trench fever, bacillary angiomatosis, endocarditis
Body lice transmission
Inoculation of faeces into the skin via scratching or inhalation of dry, powdery louse faeces from infested bedding or clothing
Where will you find body lice
On the seams of clothing - neck, axillae, waistline
Body lice treatment
Discard and incinerate infected things
If not, fumigation adn washing in >55 degree heat
Stop exposure for > 2 weeks
Cause of tungiasis
Tungas penetrans
Where is tungiasis endemic
Central and South America, Carribean, Africa, India, pakistan
What does tungas penetrans look like
Wingless fly, 1 mm in size, and likes warm, dry soil
Requires occasional blood meal
How does tungiasis develop
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
What does tungiasis look like
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
Complications from tungiasis
Secondary infection Lymphangitis Tetanus Gangrene Amputation
List of tungiasis treatments
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
Where do you find myasis
Hot tropical places in the summer
What are the most common causes of myasis?
Diptera athropods: 2 winged fly
- Human botfly - dermatobia hominis
- Tumbu fly - Cordylovia anthropophaga
Then wound:
- Screw worm - cochliomyia hominivorax in US
- Chrysomya bezziana in Australia, Africa Asia
Then creeping:
- Hypoderma bovis - cattle
- Gasterophilus intestinalis - horses
Lifecycle of the human botfly (dermatobia hominis)
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
How does C anthropophaga deposit its eggs?
Onto moist clothing and soiled blankets in the sand
Larva can live 15 days without feeding, but once hits skin it infests and matures
Clinical myasis
- 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 - 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 - Creeping or migratory
- looks like cutaneous larva migrans, but slower and persists for longer, and are larger than helminth larvae
Myasis pathology
Lots of inflammation: neuts, eos, mast cells, giant cells, lymphocytes, plasma cells
Larvae in cross-section
Myasis treatment options
- Do not forcibly remoed as its shape will prevent this
- Surgical debridement under anaesthetic - curative –> not required unless patient asks, as will come off in 2 weeks anyway
- Suffocate with occlusion - petroleum –> then will come up for air over a few hours and then capture
- LN2
- Chloroform
- Insecticides
- Ethyl chloride sprays
- Inject lidocaine to base of cavity
- Wound: debride and irrigate
- Oral ivermectin - particularly helpful for oral and orbital involvement
- Tetanus vaccination
