Guinea Worm (Dracunculus medinensis)

Overview

Transmission and Life Cycle

1. Ingested larvae penetrate the stomach or intestinal wall
2. Worms mate and mature over approximately 12 months
3. The impregnated female migrates to subcutaneous tissues, usually the lower extremity
4. She induces a blister on the skin that ruptures and forms an ulcer
5. On contact with fresh water, the female releases thousands of motile larvae - which infect new Cyclops and complete the cycle

Clinical Features

• Pre-emergence (~1 year after infection): No symptoms until just before the blister forms
• Prodrome: Sudden onset of fever, periorbital edema, wheezing, and urticaria (allergic reaction)
• Emergence: Local pain and swelling at the blister site; typically the lower leg but can occur on the genitalia, buttocks, or arms
• Complications: Secondary bacterial infection causing cellulitis, abscess, or tetanus; rarely, the worm becomes encapsulated and calcified in the tissues

Diagnosis

Treatment

Gradual mechanical extraction - slowly winding a few centimeters of the worm onto a stick each day (~1 inch/day), taking great care not to rupture it (rupture causes severe inflammation). Full extraction may take days to weeks.

Prevention

• Filtering drinking water through finely woven cloth (removes Cyclops)
• Boiling or treating water with temephos (Abate), a larvicide safe for drinking water
• Educating infected individuals not to enter fresh water while the worm is emerging
• Provision of safe wells and clean water sources

Epidemiology and Eradication Progress

• As of end-2022: only 13 human cases in four African countries (Chad: 6, South Sudan: 5, Ethiopia: 1, Central African Republic: 1)
• Remaining endemic countries as of 2023: Chad, Mali, South Sudan, Angola, and Ethiopia
• A major obstacle to final eradication is animal reservoirs - dogs and cats in Chad serve as significant reservoirs, which was not appreciated until the 2010s

Historical Note

Scabies

Overview

The Mite

• Appearance: Pearl-like, translucent, white, oval, eyeless, with 4 pairs of short stubby legs
• Size: Adult female is 0.4 × 0.3 mm (just barely invisible to the naked eye); male is slightly smaller
• Survival off the host: 3 days in a sterile environment; up to 7 days in mineral oil
• Cannot fly or jump
• A normal host harbors 3 to 50 female mites; infants and the elderly may harbor 50-250; patients with crusted scabies can harbor millions

Life Cycle

Transmission

• Primary route: Close, prolonged skin-to-skin contact (sexual and non-sexual)
• Fomites: Much less likely in normal scabies but highly relevant in crusted scabies (mites shed in huge numbers into bedding, furniture, floors)
• Incubation period: 4-6 weeks in first exposure; only 1-4 days on re-exposure (due to sensitization)

Clinical Features

Symptoms

• Intense pruritus, classically worse at night (sensitization to mite saliva, eggs, feces)
• On re-infestation, symptoms begin within 1-4 days

Distribution (classic sites)

• Interdigital web spaces of fingers
• Volar wrists and lateral palms
• Elbows, axillae
• Scrotum, penis, labia, areolae in women
• Head and neck spared in healthy adults; involved in infants, the elderly, and immunocompromised

Lesions

• Small (<5 mm) papules, pustules, and vesicles with excoriations
• Pathognomonic sign: The burrow - a thin, thread-like, linear or J-shaped tunnel 1-10 mm long in the stratum corneum

Crusted (Norwegian) Scabies

• Hyperkeratotic plaques diffusely on palmar/plantar regions
• Thickening and dystrophy of toenails and fingernails
• Minimal or no pruritus (defective immune/sensory response)
• Millions of mites - extremely contagious; can spread to anyone in the vicinity
• Environmental mite burden is enormous (6,000 mites/g of shed debris from sheets, furniture)

Diagnosis

• Skin scraping with a broad-blade scalpel from the terminal end of a burrow, placed in mineral oil on a glass slide - look for mites (330-450 μm), eggs, or scybala (fecal pellets). Low sensitivity.
• Dermoscopy (epiluminescence microscopy): Non-invasive; identifies the "delta-wing jet" or "triangle sign" of mite parts within the stratum corneum in vivo. Higher sensitivity.
• Burrow ink test: Apply black felt-tip marker to affected area, wipe off with alcohol - the burrow retains ink and becomes visible
• Reflectance confocal microscopy and PCR on swabbed skin are emerging high-sensitivity/specificity tools

Treatment

First-line

Crusted scabies

• Combination of oral ivermectin + topical permethrin is recommended (mite burden is too high for topical alone to be reliable)

Alternative agents

• Crotamiton 10% cream/lotion
• Precipitated sulfur 5-10% in petrolatum (safe in pregnancy and infants <2 months - youngest age group)
• Lindane 1% - avoid due to neurotoxicity; reserve only if all others fail or cannot be tolerated; contraindicated in children <10 years

Adjunct therapy

• Oral antihistamines and topical corticosteroids for pruritus relief (itching may persist for weeks after successful treatment due to ongoing hypersensitivity reaction)
• Topical/systemic antibiotics for secondary bacterial infection of excoriated lesions

Key Management Points

1. Treat all contacts simultaneously - family members and close contacts, even if asymptomatic (many are asymptomatic mite carriers)
2. Environment decontamination: Wash and dry all clothing, bedding, towels at high temperature; vacuum floors and furniture
3. Pruritus persisting after treatment does not mean treatment failure - the hypersensitivity reaction can last weeks
4. Hospitalized patients: Contact precautions until successfully treated

Kala-Azar (Visceral Leishmaniasis) - Characteristic Findings

What is it?

Characteristic Clinical Findings

1. Fever

• Prolonged, intermittent fever - temperatures of 39-40°C (102-104°F)
• A classic pattern is double daily temperature spikes (two fever peaks per day)
• Fever may persist for weeks to months

2. Massive Splenomegaly

• The most striking finding - the spleen can become enormously enlarged, sometimes reaching the pelvis
• Due to reticuloendothelial hyperplasia packed with parasitized macrophages
• The spleen is the most parasite-rich organ (>95% positivity on splenic aspirate)

3. Hepatomegaly

• Present alongside splenomegaly (hepatosplenomegaly is the hallmark)
• Hepatic fibrin-ring granulomas may be seen on biopsy

4. Progressive Wasting / Cachexia

• Severe weight loss, emaciation, weakness
• Patients develop a progressive wasting syndrome if untreated
• Advanced disease leads to GI symptoms and a wasting syndrome

5. Pancytopenia

6. Skin Darkening (the "Kala" of Kala-Azar)

• Patchy macular darkening of the skin due to melanin deposits
• Most marked on the forehead, temples, perioral area, and midabdomen
• Occurs in Indian patients; grayish/dark discoloration gave rise to the name
• NOT seen in all geographic variants

7. Hypergammaglobulinemia

• Marked polyclonal elevation of immunoglobulins (especially IgG)
• Basis of the Aldehyde (Napier's formol-gel) test

8. Hypoalbuminemia

• Nutritional depletion + protein loss
• Combined with hypergammaglobulinemia = reversal of albumin:globulin ratio

9. Lymphadenopathy

• Peripheral lymphadenopathy is particularly prominent in East Africa (Sudan, South Sudan)
• Less common in Asian variants

10. Secondary Complications

• Secondary bacterial infections (pulmonary, GI), noma/cancrum oris (oral ulceration)
• Hemophagocytic lymphohistiocytosis (HLH) - a recognized complication
• Tetanus and hemorrhage in late disease
• Death in ~2 years if untreated (advanced, untreated cases are almost universally fatal)

Post-Kala-Azar Dermal Leishmaniasis (PKDL)

• Indian subcontinent variant: Polymorphic lesions - hypopigmented macules/patches coexisting with papulonodules on the face and trunk
• Sudanese variant: Papular or nodular lesions
• The skin acts as a reservoir maintaining transmission even after the visceral disease is "cured"

Diagnostic Tests

1. rK39 Rapid Diagnostic Test (Dipstick) - First Line

• Immunochromatographic assay detecting antibodies to L. donovani using recombinant k39 antigen
• Results in 5 minutes; simple to perform in the field
• Mainstay of diagnosis in India
• Limitations: Do NOT use in relapse, reinfection, or HIV co-infection cases

2. Parasitological Diagnosis - Gold Standard (Confirmatory)

3. Aldehyde Test (Napier's Formol-Gel Test) - Historical

• Add 1-2 drops of 40% formalin to 1-2 mL of patient serum
• Positive: Jellification to milk-white opacity (like white of hard-boiled egg) - newsprint cannot be read through it
• Strongly positive if occurs within 2-20 minutes
• Reflects extreme hypergammaglobulinemia (nonspecific - also positive in other conditions causing hyperglobulinemia)

Epidemiology

Treatment