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
Diagnosis of scabies
Clinical presentation looking for burros
Skin scraping – identification of mites
Treatment of scabies
Permethrin cream 5%
Malathion 0.5% cream
Topical creams e.g permethrin cream
if that fails use malathion 0.5% lotion
Cream/lotion applied to whole body from neck down and left 20hrs and then washed off – repeated after 7 days
Treat all household and sexual contacts
Oral ivermectin (200ug/kg) repeated after 2 weeks because not ovicidal – highly effective as community or mass treatment
What is cutaneous larva migrans / creeping eruption / ground itch caused by?
Zoonotic hookworm larvae - Ancylostoma braziliense, A.caninum, A.ceylanicum
Epidemiology of cutaneous larva migrans
Common in tropical and subtropical regions
Only sporadically in temperate regions
Affects small children, inhabitants of poor neighbourhoods, travellers to tropical regions
Clinical presentation of cutaneous larva migrans
Tracks of larvae moving around skin, leaves proteins in wake that have inflammatory reaction.
Diagnosis by clinical presentation.
Treatment of cutaneous larva migrans
Do not survive more than 5-6 weeks in human host
Often resolves without treatment
Treatment recommended to prevent secondary bacterial infections:
- Topical thiabendazole 5-15%
- Oral albendazole 400mg for 3 days
- Oral ivermectin (200ug/kg) single dose
Tungiasis
Also known as jiggers, nigua, sand fleas
Caused by tunga penetrans that parasitizes pigs, dogs and bovines
Fertilised female digs into skin, gradually becomes bigger and more pacted with eggs and causes pain as it gets bigger
Epidemiology of tungiasis
Infestation of dogs, cats, pigs, cows and peri domestic rodents
Latin america, carribean, sub-saharan africa
Affects inhabitants of poor neighbourhoods or rural villages
Rarely travellers
Clinical presentation of tungiasis
Impacted female inside skin
Can be removed with forceps or needles
Can cause a lot of pain, severe and incapacitating
diagnosis by examination of typical lesion
Complications of tungiasis
If embedded sand-fleas are not extracted soon after penetration, superinfection may ensue
Bacterial infections
Abscesses, suppuration and lymphangitis
- Lymphoedema
- Post-streptococcal glomerulonephritis
- Tetanus
- Septicaemia/gangrene
- Disability
Treatment and control of tungiasis
Removal of embedded flea with sterile needle
More extensive infestations require surgical extraction under sterile conditions
Immersion up to ankle for 10 mins with 0.005% potassium permanganate or dimeticones of low viscosity
prevention by use of repellents and one health approach
Treatment and control of tungiasis
Removal of embedded flea with sterile needle
More extensive infestations require surgical extraction under sterile conditions
Immersion up to ankle for 10 mins with 0.005% potassium permanganate or dimeticones of low viscosity
prevention by use of repellents and one health approach
Myiasis
Caused by botfly larvae of various species
Most common are dermatobia hominis that causes furnucular lesions and cochliomyia hominivoraz that causes screwworm
Myiasis lifecycle
Catches mosquito, lays eggs on mosquito
Mosquito finds warm blooded vertebrae, larvae hatch from eggs and invade skin
Or botfly can lay eggs directly on human skin
Larvae develop inside skin and eventually drop out of skin and form pupa in soil to later develop into adult fly
Epidemiology and clinical presentaion of myiasis
tropical and subtropical regions, ecuador
Larvae in skin, pops head out, may form abscess
Spines on body so can’t be squeezed out
Fly can lay eggs on open wound which can become infested, associated with mortality, screwworm infestation
Screwworm can live in ears, palate
Complications of myiasis
Dermatobia hominis
- Secondary infections may occur after extraction
- Lesions, particularly when multiple are painful and alarming
Screwworm
- Disability
- Secondary infections
- Death
diagnosis by clinical presentation and larval extraction and identification of larvae
Treatment of myiasis
Dermatobia hominis
- Occlusion with Vaseline
- Surgical excision
- Oral ivermectin (200ug/kg) single dose
Screwworm
- Surgical extraction with debridement of dead tissue
- Oral ivermectin
- Antibiotics
Control/prevention
- One health approach
- Insect repellents/mosquito nets
Treatment of myiasis
Dermatobia hominis
- Occlusion with Vaseline
- Surgical excision
- Oral ivermectin (200ug/kg) single dose
Screwworm
- Surgical extraction with debridement of dead tissue
- Oral ivermectin
- Antibiotics
Control/prevention
- One health approach
- Insect repellents/mosquito nets
