Ectoparasites; Insecta (Fleas & Lice) Flashcards
(35 cards)
What is the latin name for the human flea? Its classical characteristics?
- Pulex irritans
- Can FLY (bites, fucks off)
- Host specific
- Actively seeks host; hormone/CO2
- Can survive prolonged starvation (1 year+)
What is the life cycle for Pulex irritans (human flea)?
Similar to Cimex lectularius (bed mite); bites and jumps off again
1) Eggs shed by female into environment
2) Eggs hatch into larvae (in 3-4 days), feed on organic debris in environment.
3) Larvae form pupae (cocoons, covered w/debris from environment)
4) Adults hatch from pupae (after 3-4 weeks of larvae-pupae stage), seek out warm blooded host for blood meals.
> Humans primary host for Pulex irritans.
What are the signs and symptoms of Pulex irritans (human flea) infestation?
- Bites grouped in clusters (bed mites; bite in a line)
How is Pulex irritans infestation treated?
- Cold compress
- Deter scratching; prevent secondary bacterial infection
- Antihistamine (oral/topical); reduce swelling/itch
What do fleas also act as (as well as being a nuisance)?
Vectors of disease:
- Plague
- Murine Typhus
What is Tungiasis, and what is it caused by? Characteristics? Prevention?
- Infestation, by the sand flea (‘Tundra’)
- AKA Chigoe/jigger flea
»> Tunga penetrans - Small size, compressed
- Females burrow into skin
- Not a vector for disease
»> Wear shoes in infected ares
What is the life cycle for Tunga penetrans (sand flea)?
1) Eggs shed by female into environment
2) Eggs hatch into larvae
3) Larvae form pupae
4) Adults hatch from pupae
5) Adult females burrow into stratum granulosum
6) Gravid female resides in subcutaneous lesion
What is the treatment for Tungiasis?
- No pharmacological treatment
- Self-limiting (bores into feet from sand, lays eggs)
- Physical extraction with pin/suffocation
What is the latin name for lice/nits? Characteristics?
- Pediculus humanus (infestation-humans)
- Cling to hair shafts (legs evolved to cling on)
- Do NOT fly or jump; CRAWL
- Can travel quickly; 25 cm/minute
- Highly contagious
- Persistent > 1 year if untreated
What types of Pediculus humanus (lice) are there, and their corresponding latin names?
- Head lice; Pediculus humanus capitis (2-3mm, capitis = head)
- Body lice; Pediculus humanus humanus (2.3mm-3.6 mm, arms)
- Pubic lice (crabs); Phthirus pubis (1.1-1.8mm, genitalia)
What is the life cycle of lice (Pediculus humanus)?
1) Eggs (nits) laid by adult female, cemented at base of hair shaft (oval, yellow-white)
2) Eggs hatch to release a nymph (6 to 9 days); nit shell is a visible dull yellow attached to hair shaft
3) 4) Nymph looks like an adult, but is size of pinhead; molts to 2nd and 3rd nymph before maturing to adult (7 days after hatching)
5) Adult louse has 6 legs (w/claws), sesame seed size. Females lay up to 8 nits/day, living for up to 30 days on a person’s head.
How long can Pediculus humanus (lice) survive without a blood feed?
- Adults need blood feed several times daily,
- Dying within 1 to 2 days off the host
What are the signs and symptoms of Pediculus humanus capitis (head lice) infestation?
- Itching
- Resulting difficulty sleeping
- Scratching; secondary bacterial infection
- Raised bumps on neck
How is Pediculus humanus (lice) diagnosis made?
Visual inspection:
- Scalp
- Comb; wet comb w/soap/shampoo, wipe onto tissue after passing through hair
Who is at greater risk of Pediculus humanus infestation?
- Girls at higher risk than boys; longer hair, sharing of fomites (brushes, combs, hats)
- 50% of 4 to 11 y/o’s catch lice
What is the treatment for Pediculus humanus capitis infestation? What stage are they effective against?
All to be used for 8 - 12 hours contact time:
1) Dimeticone lotion 4% (Hedirn/Lyclear)
- Kills adults - Does NOT kill live eggs
2) Benzyl alcohol emulsion 25%
- Kills adults/larvae - Does NOT kill live eggs
3) Malathion lotion 0.5% (Derbac-M); anticholinesterase
- Kills adults/larvae - Some ovicidal activity
What treatment for Pediculus humanus capitis is still widely used in other parts of the world, but not the UK; and why?
Lindane shampoo 1%
- Antiquated
- Causes neurological damage/death
- Still used worldwide
- Banned by the EU in 2008
How do the approved treatments for Pediculus humanus capitis, work? Counselling points?
Dimeticone: - Silicone based - Forms water impervious coat on lice - Suffocates lice >>> Give 2nd treatment (1 week later?) to kill fresh adults/larvae from eggs left behind first time
Malathion: - Organophosphorus anticholinesterase - Promotes cholinergic NT - Neurotoxic insecticide >>> Can be IRRITATING to skin/scalp >>> No more than 4 consecutive applications
How does the antiquated treatment for Pediculus humanus capitis, Lindane, work?
Gamma-hexachlorocyclohexane
- Ion channel antagonist
Neurological toxin
- Binds and inhibits GABAa chloride channel complex
- At picrotoxin binding site (blocks channel)
- Hyperpolarizes ion channel; cannot fire - GABA can’t dampen down activity, thus resulting seizures
Why is Lindane so dangerous?
GABAa is ubiquitous in Animalia:
- Interferes with mammalian central neurotransmission
- GABAa antiepileptic, dampens/inhibits neuronal activity
- Thus causes seizures and convulsions; GABAa AGONIST is used for epilepsy.
What are the prophylactic measures against Pediculus humanus capitis?
- Brushing w/ wet comb
What does the Cochrane review of head lice treatment recommend? (chemicals on children)
- Pyrethroids versus shampoo and comb
> Shampoo and comb found to be equally as effective as insecticide
> Tea tree oil; lice don’t like tea tree oil; fall off
»> Malathion (lightly toxic), Lindane (v. neurotoxic); neurotoxic insecticides, best avoided.
How does the morphology of Pediculus humanus capitis compare with Phthirus pubis?
- Head louse claw adapted for round hair; common with body and hair
- Pubic louse claw adapted for oval shaped hair; common with pubic hair and eyelashes
What are the signs and symptoms of Phthirus pubis infestation?
- Itching; inflammation from scratching
- Black powder in underwear; malted lice
- Blue-coloured spots on skin; exoskeletons
- Tiny blood spots on underwear/skin; crushed lice
Pubic AND body hair:
- Underarm, chest, leg
- Facial; beards, eyebrows
