Lice and Scabies Flashcards
What is pediculosis?
Aka lice
Ectoparasites (on the outside) that live on human hosts
There are 100s of millions of cases every year world wide
Outbreaks occur in schools, day-care centres and long-term care facilities
How common is head lice?
In North America, there prevalence is about 1-3%
Annual incidence of 25-35% in primary school children
Describe a pediculus humanus capitus
They are wingless
They about 1-3 mm long
Usually tan but they will change colour with the hair that they are in (darker hair, darker louse)
They feed on blood and they feed several times a day
They live within an inch (or even 1 cm) of the scalp (they don’t live at the ends of long hair)
Describe pediculus humanus corpis
Aka body louse
They are a bit bigger than head lice; 2-4 mm
They live and hide in the seams of the clothing
They are the only type of louse that can spread disease
Describe phthirus pubis
Aka pubic louse
Shorter and more round
Pin-sized head; 0.8-1.2 mm long
Appear yellow-brown, dot-like
Coloquial name: crabs (they resemble the crustacean)
They are more wide spread because pubic hair is a little more spread out
Where do pubic lice live?
They live in the pubic area, but are sometimes found under the armpits, in the eyelashes, in moustaches, beard and eyebrows
Describe of the a head louse
Starts as an egg
Nymphs emerge after 6-10 days (first nymph, second nymph, third nymph, adult)
Nymphs must undergo 3 molts over 10 days
The female louse can survive for 1 month and lay between 5–10 eggs per day
How long can a louse live off a host? What about an egg?
The adult can survive 1-4 days off the host
The eggs can survive off the host for about 10 days
What are risk factors for head lice?
More prevalent in school-aged children (aged 3-11)
More prevalent in females (longer hair and girls tend to play dress up and share hats and brushes)
It is NOT more prevalent when there’s a lack of hygiene (lice prefer clean hair)
What hair type do head lice prefer?
Straigh hair
African-american has a curl to it and North American lice find it difficult to graph that type of hair.
In North America, lice is more prevalent in caucasians. In Africa, the lice survive better on the cylindrical hair
What are the risk factors for body lice?
Poverty
Overcrowding
Low hygiene
What are the risk factors for pubic lice?
If a person is sexually active (females 15-19 years, males 20 years)
More prevalent in young adults
Hygiene is not a factor
How is head lice transmitted?
Head to head contact or by fomites (hats, hair accessories, brushes, towels)
Lice are very quick; head to head contact take about 30 seconds
How is body lice transmitted?
Direct body contact with infested person
Shared clothing and linens
How is pubic lice transmitted?
Mainly sexual or close body contact
Possibly fomites
Do pets increase the risk of lice?
No, lice only live on humans
What are the signs and symptoms of head lice?
Itching on the back of the head and near the ears
There are sometimes bite marks (less common)
The pillow case might have thin brown lines (fecal waste)
1/3 of kids will be asymptomatic
What causes the itching in head lice?
When the lice bite the scalp, they inject vasodilatory and anticoagulant properties that people will develop hypersensitivity (takes 2-6 weeks for development after first exposure; second exposure will take 1-2 days)
Describe nits
Aka eggs
They are 0.3-0.8 mm in diameter (lice comb should have fine teeth spaced 0.2-0.3 mm apart)
Viable nits generally blench in with hair colour and are located 4-6 mm of the scalp
What’s a pseudonit?
Not a nit
Could be dandruff
It’s easily detachable from the hair shaft (unlike a nit)
If a nice is several inches away from the scalp, what does this mean?
The patient has probably had lice for a while and it’s probably an empty nit
What are the signs and symptoms of body lice?
General itching around the waist, the wrists, etc.
It tends to be worse if the patient is wearing the clothes at night
What are signs and symptoms of pubic lice?
Itching in the genital area
The nits will be found at the base of the hair follicle and much more difficult to find than head lice
Skin irritation due to hypersensitivity
Rust coloured specks in underwear
How is head lice diagnosed?
Combing through the hair using a nit comb
If a nit is found in the hair, it’s only a modest predictor of a live infection
More than 5 nits within a cm of the scalp indicates a 32% change of live infection
The wet combing technique is recommended for diagnosis
Describe the wet combing technique
Wash hair and apply conditioner (leaving it in the hair)
Brush the hair with a normal brush to remove the tangles
It may help to separate the hair into sections with clips
Comb through hair with lice comb starting comb touching the skin of the scalp and comb to the edge of hair
Look carefully at the teeth of the comb in good light
Wipe the teeth with a piece of paper towel
Do this until the whole head has been combed through (this can take hours)
What should be considered for differential diagnosis of head lice?
Dandruff Seborrheic dermatitis Accumulation of hair cosmetics, paint flecks, or debris Pseudo-nits Psychogenic itch
What should be considered for differential diagnosis of pubic lice?
Seborrheic dermatitis
Folliculitis
Dermatophytosis (jock itch)
What should be considered for differential diagnosis of body lice?
Seborrheic dermatitis Folliculitis Eczema (atopic dermatitis) Impetigo (bacterial infection of the skin) Flea or insect bitse Bed bugs
What is scabies?
Highly contagious infestation of the skin with the human mite Sarcoptes scabies var hominid
Children, mothers of young children, sexually active adults and elderly in nursing homes are at greatest risk
Epidemics occur in poor living conditions (poverty, poor hygiene, overcrowding) and institutions
Describe the scabies mite
Translucent, pearly white, flat
4 legs (compared to 6)
Generally there will be 10-15 mites on the body (there’s one exception)
They are difficult to see with the naked eye
They are a mite that burrow under the skin and create a little trail
As they go along, they leave behind their feces and eggs
How many eggs do scabies mites lay?
2-3 eggs per day, with a 15-30 days lifespan
The eggs hatch after 3-4 days and go through a molting process
How long can scabies mites live off a host?
Maximum 3-4 days
Describe scabies transmission
Primarily skin to skin contact but it can also be transmitted by fomites, such as couches, towels (extremely rare, unless the patient has a high parasite load)
What are the signs and symptoms of scabies?
Itch
Classically, there will be burrows between the webs of fingers
It may take 4-6 weeks for symptoms to develop for individuals without previous exposure (with previous exposure it takes 1-4 days)
It looks like almost anything (shingles, poison ivy, etc.), which is why it is important to refer these patients to the doctor to get a proper diagnosis
Scabies is very difficult to diagnosis
What is Norwegian or “crusted” scabies?
Atypical scabies presentation Tends to occur in immunocompromised individuals There are thousands of millions of mites Lesions are not as red It's more crusty and there's flakiness
What should be considered for differential diagnosis of scabies?
Seborrheic dermatitis Impetigo Body lice Bed bugs/insect bites Eczema (atopic dermatitis)
