Scabies and Lice Flashcards
Define scabies
Skin infestation by a parasitic burrowing mite, Sarcoptes scabei, that is usually spread by skin to skin contact
What populations is scabies common in? What are the risk factors?
Common in children, young adults and elderly
Risk factors:
- Poverty and overcrowding
- Institutional care, such as rest homes, hospitals, prisons
- Refugee camps
- Individuals with immune deficiency or that are immune suppressed
- Low rates of identification and proper treatment of the disease
What is the 7 year itch?
Chronic undiagnosed scabies
*Note: it is easily missed - should be considered in any patient of any age with persistent generalized pruritus
Scabies spread
- quick infestation (holding a child’s hand), can be sexually transmitted and can be spread via bedding (hotels common)
- 3-4 weeks from initial exposure to develop symptoms
What is the reproductive cycle of scabies mites?
Male mites die after impregnating females –> females lay ~3 eggs a day that take 10-14 days to hatch –> females life span is 1 month
Scabies clinical exam
- Wide range of clinical responses
- Excoriations and eczematous dermatitis that favors the interdigital webs, sides of fingers, volar aspects of the wrists and lateral palms, elbows, axillae, scrotum, penis, labia, and areolae in women
- Head and neck are usually spared
How does scabies appear on the skin?
- Burrows appear as 0.5–1.5 cm grey irregular tracks in the web spaces between the fingers, on the palms and wrists.
- Thin thread-like linear “tunnel”
- Excoriations causing erosions are common and can destroy burrows
- Vesicles may also be present
- Red itchy nodules to penis, scrotum are scabies till proven otherwise
Complication of scabies
Often impetiginized with staph or strep bacteria from repeated scratching
Define crusted scabies
- previously called ‘Norwegian scabies’
- a very contagious variant of scabies in which an individual is infested by thousands or millions of mites living in the surface of the skin.
Tx/dx of crusted scabies
- difficult to treat due to extent of infestation (common to become repeatedly infested due to living conditions)
- sometimes requires a biopsy due to significant crusting and thickening of the skin
Dx of scabies
- definitive diagnosis when mites, eggs, egg casings or feces are found from the burrows or vesicles and is identified microscopically
- usually diagnosed clinically based on history and exam – solidified by response to tx.
When should you consider scabies?
- itchy, red, rash unresolved or unaffected by prednisone is scabies till proven otherwise
- itchy, red, rash starting in finger/toe webs, wrists, waist band, genitalia, consider scabies
Tx of scabies
- *No OTC meds are approved for scabies treatment
- 5% permethrin (elimite) is treatment of choice (unless under 2 months old)
- ivermectin 200mcg/kg on day one, then repeat in 1 week: not FDA approved
- 5–10% Precipitated sulphur ointment if allergic to above or if < 2 mo
- Crotamiton cream/lot 10% (Eurax): not FDA-approved for children
- Lindane lot 1% - not recommended 1st line: overuse or accidental swallowing can be toxic to nervous system
Patient education regarding tx of home and body after scabies
- Clean bedding in hot water, vacuum carpeting/furniture on treatment days
- Will have post-scabetic pruritus (this is from feces and can last 2 months)
Tx of residual scabies pruritus
antihistamines:
- Hydroxyzine HS, Benadryl HS, daily Zyrtec or Claritin
- Topical steroid cream/lot
Define pediculosis
This is infestation with lice (plural, louse is singular)
How are lice transmitted?
close personal contact or contact with contaminated combs, hats, pillows, clothing, and bed linen
What are lice?
- small insects that live on human hair and clothing and can be seen with the naked eye.
- often they are well-camouflaged and reflect the color of the surroundings.
- lice are ectoparasites, meaning they live ‘on’ rather than ‘in’ a host
Biology of lice
- Lice are (< 2 mm in size) wingless and have six legs on which are attached strong claws that they use to grasp on tightly to hair shafts or clothing fibers.
- Their piercing mouthparts puncture the skin to feed on human blood.
- Lice can survive for up to 10 days without feeding if they become detached from their human host.
Biology of lice continued
- Lice feed approximately 5x daily and do so by piercing the skin with their claws and injecting irritating saliva and then sucking the human’s blood
- The saliva induces pruritus
- Life cycle from egg to egg is one month
- -Egg incubates 8-10 days
- -Maturity is day 18
Which species of lice infects the head?
Pediculus humanus capitis
Which species of lice infects the body?
Pediculus humanus corporis
Which species of lice infects the pubic region?
Pthirus pubis
AKA crabs :)
Etiology of pediculosis capitits
- Usually occurs in children, uncommon in adults
- Lice about the size of sesame seed.
- Girls > boys
- Most commonly involves back of head, neck and behind the ears
- African-American children are less commonly affected, perhaps because their hair shape or texture creates a less amenable environment
S/sx seen with pediculosis capitis
- pruritis with papular urticaria &/or excoriations esp on nape of neck
- scratching causes secondary bacterial infection
- avg incubation before sxs 4-6 weeks
- *posterior cervical adenopathy without obvious disease is characteristic and should strongly suggest this disease
Differentiating between pediculosis capitis and dandruff
- Egg capsules, nits, cemented to hairshaft - very difficult to as opposed to dandruff which is easily removed
- Nits within 1 cm of scalp- confirmation active infestation
Etiology of pediculosis corporis
-lice are slightly larger than head louse but looks similar
-is a disease of the unclean so in the homeless, addicts and alcoholics
uncommon**
-vector for spread of systemic illnesses - typhus, relapsing fever and trench fever
-these lice live in clothing and return to skin surface only to feed-so are only rarely seen
-bite reaction, excoriations and secondary bacterial infections.
Etiology of pediculosis pubis
- a sexually transmitted disease
- very common problem
- no sexual or racial differences
- chance of acquiring lice from a single exposure is 90% as opposed to syphilis which is 30%**
- smaller and wider than head lice and resembles tiny crab
Location of pediculosis pubis on the body
- MC located on pubic hair, but may spread to involve anal area
- in hairy subjects, may spread to thighs, abdomen, axillae, chest and beard
S/sx of pediculosis pubis
- Majority complain of pruritus and half of these have no or little inflammation-so pruritus without rash is characteristic
- May have red papules and wheals from bite reaction
- 30% of adults infected with lice will also have another STD
Environmental treatment for head lice
- Clean bedding in hot water (at least 130 deg F)
- Vacuum furniture
- Place unwashable items in plastic bag x 2 weeks
Treatment of body lice
- Improvement of personal hygiene
- Regular (at least weekly) change of clean clothes
- Clothing, bedding, and towels laundered using water at least 130 degrees F and dried using hot cycle
- Usually pediculicide not needed but if so, follow head lice recommendations
Treatment of pubic lice
- OTC 1% permethrin or a mousse containing pyrethrins and piperonyl butoxide
- Lindane shampoo not first-line
- RX Malathion lot 0.5% (Ovide) – not FDA approved for pubic lice
- RX topical or oral Ivermectin – but only topical is FDA approved for lice
