Introduction: The Uninvited Guest

Scabies is a highly contagious skin condition caused by the microscopic mite Sarcoptes scabiei var. hominis. Affecting over 200 million people worldwide at any given time, scabies has been dubbed the “seven-year itch” not because it lasts that long untreated, but because of the relentless, persistent itching it causes [1]. Despite its prevalence, scabies remains misunderstood, stigmatized, and often misdiagnosed. The good news? It’s completely curable with proper treatment.

The Mite: Know Your Enemy

The scabies mite is an arachnid, related to spiders and ticks. The female mite burrows into the outer layer of skin (stratum corneum), laying 2-3 eggs daily as she tunnels at an impressive rate of 0.5-5mm per day [2]. She lives for about 4-6 weeks, after which she dies at the end of her burrow.

The intense itching associated with scabies isn’t from the mite itself but from an allergic reaction to the mite’s saliva, eggs, and feces (scybala). This delayed-type hypersensitivity explains why first-time infestations may not itch for 2-6 weeks, while reinfestations trigger symptoms within 1-4 days [3].

Transmission: How Scabies Spreads

Scabies spreads through prolonged skin-to-skin contact. Brief handshakes or hugs rarely transmit the mite, but the following situations pose high risk:

• Sexual contact: A common mode of transmission in adults
• Household contacts: Living in close quarters
• Institutional settings: Nursing homes, prisons, dormitories
• Sharing bedding, clothing, or towels: Mites can survive off the host for 24-36 hours at room temperature [4]

Clinical Presentation: What to Look For

Classic Scabies

Distribution: Scabies favors specific body sites:

• Web spaces between fingers (most common)
• Flexor surfaces of wrists
• Elbows and armpits
• Waistline and beltline
• Buttocks and genitalia (in men)
• Nipples and areolae (in women)
• Soles of feet (in infants)

Lesions:

• Burrows: Thin, wavy, grayish-white lines (2-15mm) – pathognomonic but often excoriated away
• Papules and vesicles: Red, raised bumps
• Excoriations: From scratching
• Secondary infection: Impetigo from bacterial superinfection

Symptoms:

• Intense itching, worse at night (hallmark feature)
• Family members or close contacts with similar symptoms

Crusted (Norwegian) Scabies

A severe form occurring in immunocompromised, elderly, or neurologically impaired individuals. Patients harbor thousands to millions of mites (vs. 10-15 in classic scabies) with thick, crusted lesions containing abundant mites. These patients are highly contagious [5].

Diagnosis: Confirming the Infestation

Diagnosis is primarily clinical, based on history and examination. Definitive diagnosis requires:

• Microscopic examination: Mineral oil scraping of burrows reveals mites, eggs, or feces
• Dermoscopy: Burrows appear asa “jet-with-contrail” pattern

Treatment: Eradicating the Mite

First-Line Therapies

Permethrin 5% Cream (Elimite):

• Application: Apply to the entire body from the neck down (including under nails, between fingers/toes, genitals). Pay special attention to web spaces, wrists, elbows, axillae, and buttocks.
• Duration: Leave on for 8-14 hours (overnight), then wash off
• Repeat: Second application one week later
• Efficacy: 90% cure rate with two applications [6]

Oral Ivermectin (Stromectol):

• Dosing: 200 mcg/kg orally, repeated in 7-14 days
• Indications: Alternative for patients who cannot tolerate topical therapy, institutional outbreaks, or crusted scabies
• Note: Not FDA-approved for scabies but widely used off-label

Special Considerations

Crusted Scabies:
Requires combination therapy: topical permethrin + oral ivermectin (multiple doses over weeks), often with keratolytic agents to remove crusts [7].

Pregnancy and Lactation:
Permethrin is pregnancy category B and considered safe. Ivermectin is avoided in pregnancy.

Infants and Children:
Permethrin is safe. Treat the entire body, including scalp, face, and ears (common sites in infants).

Environmental Decontamination

To prevent reinfestation:

1. Wash all bedding, clothing, and towels used in the past 3 days in hot water (≥60°C) and dry on high heat
2. Items that cannot be washed should be sealed in plastic bags for 72-96 hours (mites die without a human host)
3. Vacuum carpets and furniture – discard the vacuum bag immediately
4. Treat all close contacts simultaneously, even if asymptomatic, to prevent ping-pong transmission

Managing the Itch

Antihistamines (cetirizine, diphenhydramine), calamine lotion, and topical corticosteroids can relieve itching. Important: Itching may persist for 2-4 weeks after successful treatment due to ongoing allergic reaction to dead mite debris.

When Treatment Fails

Treatment failure occurs in 5-10% of cases due to:

• Incorrect application
• Missed areas
• Failure to treat contacts
• Reinfestation from the environment
• Permethrin resistance (rare)

A second course or switching to oral ivermectin is recommended for persistent cases.

Complications

• Secondary bacterial infection: Impetigo, cellulitis, abscesses
• Post-streptococcal glomerulonephritis: In developing countries
• Eczema and lichenification: From chronic scratching

Prevention: Breaking the Cycle

• Avoid skin-to-skin contact with infested individuals
• Practice good hand hygiene
• Avoid sharing bedding, clothing, or towels
• In institutional settings, prompt diagnosis and mass treatment of exposed individuals

Conclusion: Itch No More

Scabies is an ancient affliction that remains remarkably common, but modern treatments make it readily curable. The keys to success are:

1. Correct diagnosis with a high index of suspicion
2. Meticulous application of scabicides
3. Treating all close contacts simultaneously
4. Environmental cleaning to prevent reinfestation
5. Patience with post-treatment itching

With these steps, the “seven-year itch” can be eliminated in a matter of weeks.

References:
https://www.medicalnewstoday.com/articles/crusted-scabies
https://go.drugbank.com/articles/A2984
https://emedicine.medscape.com/article/1109204-overview
https://www.truemeds.in/diseases/skin/scabies-258
https://www.emedicinehealth.com/scabies/article_em.htm

Medications that have been suggested by doctors worldwide are available on the link below
https://mygenericpharmacy.com/category/products/skin-care/scabicide

Disclaimer: This article provides educational information about scabies. If you suspect scabies, consult a healthcare provider for proper diagnosis and treatment.