What is scabies?
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Hello and welcome to the Medical Fun Facts Podcast.
It’s Monday 27 November 2017. My name is Gary and the Medical Fun Facts Podcast is a weekly show with a few facts and hopefully one or two funny lines. Don’t expect too much and everything will be okay.
Last week, in episode 93 I spoke about “R is for Rubella”, and gave a little insight into why I love microbiology.
Tonight, I’m speaking about S is for Scabies.
What is Scabies?
Scabies is caused by a parasitic mite infestation of the skin. You can see the infestation as papules, vesicles, or burrows containing the mites and eggs. Itching or pruritus is intense, especially at night, the scratching can lead to secondary bacterial infections.
Lesions are usually found in the webbing between your fingers, the ‘inside’ surfaces of wrists and elbows, in your armpits, and belt line and thighs. In women, your nipples, abdomen, and the lower portion of your butt cheeks are often affected in women and in men your penis and scrotum can harbour these mites with their eggs. In infants, the head, neck, palms, and soles may be involved.
In senile patients plus those with an immunodeficiency, the infestation can become generalised and crusted giving rise to Norwegian or crusted scabies. In this situation, the pruritus may not be as intense but secondary bacterial infection with β-hæmolytic streptococci and golden staph can occur sometimes with an associated bacteræmia. Infection with Streptococcus pyogenes can give rise to acute glomerulonephritis which may result in kidney failure and unless treated properly can result in end stage renal failure which may then require renal dialysis or a renal transplant. Unfortunately, the life span of people with kidney failure is cut short.
When I worked in the Northern Territory of Australia, severe crusted scabies infection was sadly all too common in Australian Aboriginal men and women. The complications were devastating. The amount of skin and kidney disease amongst Australia’s Aboriginal and Torres Strait Islander peoples is very high and the associated morbidity and mortality is just awful.
I prefer to use the term severe crusted scabies rather than Norwegian scabies because I understand Norwegians are understandably unhappy about associating such an ugly disease with their country. I have photos but I really don’t want to use them on the show notes. Just imagine your entire surface area raised, lumpy, lots of raw areas from scratching, large long and wide fissures in your skin because of poor dermal integrity and lots of pus in pustules caused by secondary bacterial infection. When I say all over, I mean all over your skin.
Scabies is caused by Sarcoptes scabiei var. hominis.
The diagnosis is by visual examination of the papules. Scabies infestation can be confirmed by recovery from a burrow and microscopic identification of the mite, eggs, or mite faeces (scybala or the singular scybalum). It’s best to avoid scraping burrows that have been excoriated. If you apply a little oil to a burrow it helps when scraping with a sharp blade to get the mites and eggs and faeces out so you can use the tip of the blade to apply the material to a glass slide. You can also use some ink on the skin to help see where burrows are. Just put some ink on the affected area, leave it a little while and then wipe it off. The ink will penetrate the shallow burrow and you can see where to apply your blade.
Where in the world does scabies occur?
You can find scabies all over the world and it’s assumed scabies outbreaks occur due to overcrowding, poverty and poor sanitation. I know when I did some sexual health as a trainee I saw patients with new infestations who had been staying in backpacker hostels. They told me they had been enjoying sexual activities with other guests of the hostels, and doing quite a bit of bed hopping. I suppose it’s one way for a parasite to travel the world.
Humans are the only reservoir of Sarcoptes scabiei var hominis.
In persons without previous exposure the incubation period is 2–6 weeks. If you have been previously infested you may develop symptoms 1–4 days after reexposure.
Transfer of parasites commonly occurs through prolonged direct contact with infested skin and also during sexual contact. Mites can burrow beneath the skin surface in about 1 hour. Persons with the crusted scabies are highly contagious because of the large number of mites present in the exfoliating scales. We’re talking about millions of mites. At the Royal Darwin Hospital, researchers from the Menzies School of Health Research would take the bed sheets from patients with severe crusted scabies and count the mites. These patients shed millions of mites.
Transmission can occur until mites and eggs are destroyed by treatment, ordinarily after 1 or occasionally 2 courses of treatment 1 week apart. Crusted scabies can require multiple treatments with one or more agents to eliminate an infestation.
Risk groups include household members and sexual partners of persons infested with scabies and other persons living in conditions in which close body and skin contact is common. When scabies outbreaks occur, they tend to be in nursing homes, child care centres, extended-care facilities, and prisons. The risk groups for severe crusted scabies are immunocompromised, elderly, disabled, or debilitated persons.
Prevention requires education of the public and medical community on mode of transmission, early diagnosis, and treatment of infested patients and contacts.
Management of patient
Managing people infested with scabies includes a few modalities including isolation, disinfestation and treatment of the infestation. Infested individuals should be excluded from school or work until the day after treatment. For hospitalised patients, they should be isolated for 24 hours after start of effective treatment.
A day may be insufficient for severe crusted scabies because viable mites can remain after a single treatment. In an institutional outbreak of crusted scabies, 10-day isolation of the index patient may be necessary.
Concurrent disinfestation involves washing clothing and bedding worn or used by the patient in the 48–72 hours prior to treatment may sometimes be needed for recurrent infestations or for people with severe crusted scabies. Using hot cycles of both washer and dryer will kill mites and eggs.
The treatment of choice, particularly for children and pregnant or nursing women, is topical permethrin (5%). Other topical therapies include lindane (1%). Because of concerns about neurotoxicity, lindane should only be used in patients who cannot tolerate or have failed treatment with safer medication.
Oral ivermectin has been shown to be effective against scabies but may not be licensed for this use in some countries. A repeat treatment with oral ivermectin may be necessary after 7–10 days if eggs survive the initial treatment. Resistance has been reported for all scabicides.
Topical agents need to be applied to the whole body except the head and left on for the prescribed time. These agents are then washed off. On the following day, the patient should have a cleansing bath and change to fresh clothing and bedding. Itching may persist for 1–2 weeks; this should not be regarded as a sign of drug failure or reinfestation. Overtreatment is common and should be avoided because of toxicity of some of these agents, especially lindane.
Questions for readers and listeners
Have you ever had scabies?
Did you know you could get scabies from sexual contact?
Can you imagine the discomfort of intense itchiness of your penis or vulva?
Please leave your answers in the comments section of the show notes or on the Facebook page or on YouTube.
That’s episode 94 in the can.
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I’ll catch you next week for episode 95. Something beginning with the letter T. Send me suggestions.
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Thank you, and good night.
On my ‘professional’ Facebook account and page, occasionally people leave comments relating to my work with the Australian Government Department of Health. I will not engage in public on social media with work-related matters. Please send me an e-mail to Gary.Lum@Health.gov.au Specifically these topics include poliovirus containment, security sensitive biological agents, Lyme disease, debilitating symptom complexes attributed to ticks (DSCATT), electromagnetic energy and electromagnetic hypersensitivity, and biological importation risk assessment.