Scabies Infestation on Darker Skin: Epidemiology and Etiology

00:01 Welcome to our lecture on scabies.

00:08 Scabies is a transmissible skin infestation caused by the host specific mite, Sarcoptes scabiei. It's a relatively common infestation that affects individuals of any age and socioeconomic status.

00:27 The worldwide prevalence is about 200 million people, and the following are the risk factors for developing scabies.

00:41 Sarcoptes scabiei is a whitish brown eight legged mite and it is responsible for the condition called scabies.

00:53 Transmission could be due to direct and prolonged skin-to-skin contact.

00:59 Sometimes it can be transmitted through fomites, that is, clothing, bed, clothes, etc.

01:08 but these are uncommon ways of scabies transmission.

01:13 So let's take a look at the life cycle of the mite.

01:16 Scabies. The male mite fertilizes the female on the surface of the skin.

01:24 The male mite dies and the female starts burrowing into the stratum corneum.

01:30 The female lays 2 to 3 eggs per day.

01:33 It continues to burrow 0.5 to about five millimeters per day for about 4 to 8 weeks.

01:41 Then the eggs hatch into larvae.

01:43 After 2 to 5 days, it takes three weeks for larva to mature into adult scabies mites.

01:49 After maturation, the mites migrate to the surface and the cycle continues.

01:56 So that is the pathogenesis of scabies.

02:02 So, how does scabies present? It can present with multiple small erythematous papules.

02:09 Of course, in dark skin, the erythema may not be conspicuous, and patients may present with just skin colored papules.

02:19 Excoriations due to severe pruritis that worsens at night may also be observed, and this is a result of Th1 mediated hypersensitivity.

02:32 The practice is typically occurring at night.

02:39 The burrows may be seen there about 2 to 15mm thin, gray, red, or brown serpiginous lines on the skin.

02:49 Some of the sites that are favored by the scabies might include the sides and webs of the fingers. All these areas flex aspects of the wrist over here, extensor aspects of the elbows and the anterior and posterior axillary folds.

03:12 Sometimes one can have the lesions affecting the area around the nipple, particularly in women and male genitalia.

03:22 You can also involvement of that get involvement of that area as well as extensor surface of the limbs. Some patients may also get involvement of the buttocks and adjacent thighs. We spoke about the classical scabies presentation.

03:41 Now we're going to talk about crusted or Norwegian scabies.

03:46 It occurs in the presence of conditions that compromise cellular immunity, for example HIV and Aids.

03:53 It begins as poorly defined erythematous patches that quickly develop prominent scale.

03:59 And again do note that in black skin that erythema may not be obvious.

04:05 Pruritis may be minimal or absent in crusted scabies.

04:11 And here you can see a picture of a patient with crusted scabies.

04:16 The thick plaques. Some popular, and there's extensive thickening and scaling here. You can see the, um, the axilla, and you can see the crusted patches and some isolated papules.

04:33 In cases of extreme immunosuppression, it can actually become generalized.

04:38 And cases of electrodynamic crusted scabies have been described, meaning that more than 90% of the body surface area is involved.

04:48 But this occurs more commonly in immunocompromised patients.

04:55 So again, crusted crusted scabies occurs more frequently in the older adults and people with intellectual disabilities because of the inability to scratch, because the more you scratch, you get rid of the scabetic mite .

05:13 The complications of scabies include secondary, staphylococcal, or streptococcal infection.

05:19 You may also get axiomatization of scabies Lesions.