Micro- Lice and Scabies Flashcards
What are the 2 chilopods?
Describe their structure. How do they differ?
Where are they usually located?
Millipedes and centipedes
- both are elongated, multi-segmented
- centipedes have poison claws, millipedes do not
They are found in leaf litter [usually in the tropics]
Bites are accidental or occupational and rarely fatal
What species is the tongue worm?
Describe the structure.
What syndrome do they cause?
Pentastomid [not insect or worm]
- blood sucking endoparasite of reptiles, birds, mammals
- 2 body segments [cephalothorax, abdomen]
Halzoun syndrome [essentially a hypersensitivity]
- cough
- sneeze
- nasopharyngeal discomfort
What are the 2 types of crustacea?
What is each an intermediate host for?
- Copepod [water flea] is intermediate host for diphyllobothrium latum [tapeworm]
- Decapod [prawn, shrimp, lobster, crab] is the intermediate host for the flatworm Paragonimus westermani
Describe the structure of Arachnids.
What are the 2 major type?
Spiders and scorpions are arachnids.
They have 8 legs [4 pairs]
NO antennae
NO wings
2 body regions {cephalothorax, unsegmented abdomen]
Where do loxosceles reclusa live?
What do they cause?
Brown recluse spiders live in dark, cool places.
If they bite, they cause local necrosis that may sometimes need debridement.
What area of the body do the following mites infect?
- demodex folliculorum
- demodex brevis
Where do they live their entire life cycle?
How does rate of infection with these mites increase with age?
What percent are infected as adults?
Folliculorum = hair follicles on the face Brevis = sebaceous glands on body and head
Entire life cycle is in the follicle/gland
Rates are rare in childhood, increase at puberty and by adulthood 98-100% are infested
What family does the chigger/house mite belong to?
What is their regional distribution?
Describe how they elicit response from hosts?
How is the host treated?
They are trombiculidae which have a worldwide distribution as ALLERGENS.
The larvae feed on blood and then drop off. There is NO infestation.
Host has hypersensitivity rxn whh is treated with antihistamines, topical corticosteroids
What skin disease is caused by the “itch mite”?
What is the mite species? [RED]
How large are they?
What is their body structure?
Itch mites cause scabies.
- sarcoptes scabiei [RED]
They are 300-400nm long with sac-like bodies and 8 pairs of legs.
Describe the scabies life cycle.
- female mite burrows into the epidermis
- she lays 2 to 3 eggs daily
- Larvae hatch in 3-4 days
- 17 days later, the larvae are adults where they mate.
- male dies after mating, female lives for a month or 2 living in the burrow and continuing to lay eggs
What is the distribution of scabies?
You see linear red streaks:
- fingers and toes
- behind the knees
- intertriginous areas [groin, below breast]
- wrists
What is the primary symptom of scabies?
Itching - occurs at burrows in the “characteristic locations”
What causes the hypersensitivity reaction to scabies?
Hypersensitivity is to the mite and the egg
Who does Norwegian Crusted Scabies usually occur in?
What 2 things characterize Norwegian Scabies from classic scabies?
It usually occurs in immunocompromised patients:
- HIV
- HTLV-1
It is characterized by:
- severe scaling - cm to inches thick
- tremendous number of mites- 100s to 1000s
How is scabies diagnosed?
- Clinical
- pruritic patient
- typical distribution and appearance of lesions - Scraping and microscopy
- biopsy
What is treatment for scabies?
Which is usually reserved for norwegian crusted scabies?
- permethrin
- hexachloroyclohexane
- Ivermectin - RESERVED FOR NORWEGIAN
- wash clothing in boiling water, bath, treat contacts
What is the body structure of lice?
Insects so:
- 3 body segments [head, thorax, segmented abdomen]
- six legs
- antennae
What are the 3 types of lice?
- pediculosis humanis corporis
- human body louse - pediculosis humanis capitis
- human head lice - phthirus pubis
- crab louse
Describe the life cycle of lice.
- eggs are laid on human hair follicles or on clothing [contained in a nit]
- one week : eggs–> nymph
- 3 nymph stages–> mature adults
- Lay 200-300 eggs during the lifetime before dying
What 2 types of lice complete their life cycle on the human body?
Which type lays eggs on the fibers of clothing and feed periodically on humans for blood meal?
Head lice and crabs = human body
Clothing = body louse
What is the regional distribution of lice?
What 2 things does incidence of lice correlate with?
It is cosmopolitan [worldwide, no class differences]
Incidence correlates with:
- crowded environment
- prison
- schools - poor personal hygienge
How is lice transmitted?
- Person -to-person
2. Fomites - clothing, towels, bedding
How long can lice survive in the environment without a blood meal? [RED]
What does this mean for treatment? [RED]
2 weeks
Treatment must often be repeated
What are common symptoms of lice?
- pruritis [primary symptom]
- excoriations from scratching–> secondary infections/impetigo
- macules and papules
How is lice diagnosed?
- examine hair for nits
2. examine skin for adults
What is treatment for lice and scabies?
Permethrin [DRUG OF CHOICE FOR EACH]
- hexachlorocyclohexane
- malathion
Disinfect environment, bedding, clothing
Treat contacts.
MAY NEED TO REPEAT [RED]
What is the mechanism of action of permethrin?
Is is a semisynthetic pyrethrin that is used as:
- insecticide
- neurotoxin
It prolongs activation of Na channels which kills adults [not eggs]
How is permethrin delivered for scabies and lice?
What is the 1st course efficacy? Second course?
What are the 3 benefits that make it 1st choice for scabies/lice?
Scabies- 5% shampoo/lotion given overnight
Lice- 1% shampoo/lotion given 10min
Efficacy for 1 treatment =70%, 2 =95%
Benefits
- neurotoxin has lowest toxicity
- not absorbed well across skin
- easily biodegradable
What is the mechanism of action of hexachlorocyclohexane?
What is the major benefit?
What is the major drawback/who is this contraindicated in?
It acts on GABA Cl channels at the NMJ of arthropods
Pro:
Highly specific for insects
Cons:
- Absorbed through skin with highest in : neonates, kids, elderly [thin skin] so it is contraindicated for these populations as well as pregnant/breast-feeding women
- tics, seizures, permanent damage
What is the mechanism of action for ivermectin to treat scabies?
What are pros?
What are cons?
It acts on GABA -gated Cl channels at arthropod NMJ
Pros:
- specific for insects causing paralysis
- very little neurotoxicity
- doesnt cross BBB
Cons:
Reserved for Norwegian scabies
What is the mechanism of action of malathion?
Why is is not used very often?
ACHEI at the neuromuscular junction causing tonic paralysis of the lice.
*smells bad, oily, toxic
