Ectoparasites Flashcards
What are ectoparasites? And some common ones?
Ectoparasites are organisms that live on or in skin or outgrowths of skin or another organism.
- Lice / pediculosis
- Scabies
- Cutaneous larva migrans
- Myiasis – fly larve
What are the three types of lice?
Lice are highly specialised blood sucking parasites that live on a single host species.
The head louse – pediculus humanus capitus
Public louse – Phthirus pubis
Body louse – pediculus humanus corporis
What is the life cycle of lice?
Starts as egg on hair, nit
Egg hatches, goes through various stages before becoming male or female adult
Takes about 10 days from nymph stage to egg laying female
Epidemiology of lice
Head lice
- Ubiquitous in school kids
Body lice
- Poverty and poor hygiene
- Homeless, refugees
Pubic lice
- Sexual contact
Head lice symptoms
Symptoms include itching of scalp, neck, behind ears
Common in children
Transmission direct head to head contact or sharing hair stuff
Body lice symptoms
Body lice (pediculus humanus corporis)
Symptoms: itching, bite marks on body
Most common in communities dealing with poverty, overcrowding and poor personal hygiene
Transmission: body lice living in clothing and affect the body
Pubic lice symptoms
Public lice (pthirus pubis)
Symptoms: itching of the pubic area, bluish colored sore
Transmission: direct sexual contact, not spread by toilet seats
Complications of lice
Secondary bacterial infections e.g impetigo
Allergic reactions to louse saliva
Body lice are vectors to infectious diseases – epidemic typhus (Rickettsia prowazekii), Trench fever (Bartonella quintana), louse-borne relapsing fever (borrelia recurrentis)
Diagnosis of lice
Clinical inspection of affected areas
- Head
- Body and clothes
- Pubic area
Combing with louse comb for nits
Treatment of lice
Transmission is through close hair to hair, skin to skin or sexual contact
Treatment recommended for those with active infection and close contacts with tropical pediculicides
- Standard treatment pyrethrin shampoo or lotion 1%
- Other lotions: benzyl alcohol 5%, ivermectin 0.5% and malathion 0.5%
Treatment should be repeated after 9-10 days because treatment doesnt affect nits, have to wait for nits to hatch
Overall ivermectin (single dose 100ug/kg) repeated after 9-10 days
Treatment of body lice
Machine wash all washable clothing and bed linens that the infected person touched during the two days before treatment to kill lice and nits. Use hot water cycle (130 F/ 55 C) to wash clothes. Dry laundry using hot cycle for at least 20 mins
Fumigation or dusting with chemical insecticides sometimes is necessary to control and prevent the spread of body lice for certain diseases (epidemic typhus)
What is scabies?
A mite caused by sarcoptes scabiei var hominis
- Female lays eggs
- Egg develop into larva, nymph and then adult female
- Adult female creates burrow under skin where it lays eggs
Epidemiology of scabies
Ubiquitous geographic distribution - common in latin america, china, southeast asia, indonesia
Transmission requires prolonged skin to skin contact
Higher prevalence in conditions of poverty
- Infants
- Homeless
- Refugees
- Inhabitants of poor neighbourhoods
Sexual transmission
Clinical presentation of scabies
Intense pruritus (itching), especially at night
Papular rash (pimple like)
Scales or blisters
Track like burrows, raise where female lays 10-25 eggs
Scabies complications
Sleep disturbances due to itching, can cause economic impact
Crusted scabies
Secondary infections like impetigo that can cause local skin infections, septicaemia sig fatality rate, glomerulonephritis, rheumatic fever
