Filarial and Related Infections¶

Chapter 240 | Part 5: Infectious Diseases · Part 5 – Infectious Diseases: Parasitic · Chapter 240

Key Clinical Points¶

Filarial worms are nematodes inhabiting subcutaneous tissues and lymphatics, transmitted by specific arthropods (e.g., mosquitoes).
The endosymbiont Wolbachia is present in all stages of Brugia, Wuchereria, Mansonella, and Onchocerca species and serves as a target for chemotherapy.
Lymphatic filariasis diagnosis relies on microfilariae (timing-specific), circulating antigens (>98% specificity), or ultrasound ('filarial dance sign').
Diethylcarbamazine (DEC) is the drug of choice for active lymphatic filariasis (6 mg/kg daily for 12 days) but is contraindicated in patients with high Loa loa microfilaremia (>30,000 microfilariae/mL).
Ivermectin treatment for Onchocerciasis is contraindicated in areas co-endemic for Loa loa due to risk of severe encephalopathy.
Tropical pulmonary eosinophilia (TPE) is treated with DEC (4–6 mg/kg for 14 days).
Abdominal angiostrongyliasis (Angiostrongylus costaricensis) presents as eosinophilic ileocolitis and requires specific anthelmintic regimens or surgery.
Onchocerciasis ('river blindness') causes skin atrophy, 'sowdah' (hyperpigmented dermatitis), and ocular damage (corneal scarring, optic atrophy).
Loiasis features Calabar swellings (evanescent angioedema) and subconj1tundial worm migration.
Mass drug administration (MDA) with albendazole/DEC/ivermectin is the standard for public health elimination of lymphatic filariasis.

1. DEFINITION & OVERVIEW¶

Filarial worms are nematodes that dwell in subcutaneous tissues and lymphatics. Eight filarial species infect humans, transmitted by mosquitoes or other arthropods through a complex life cycle involving larval stages and adult worms.

• Key Species: - Wuchereria bancrofti (most common) - Brugia malayi - Brugia timori - Onchocerca volvulus - Loa loa - Mansonella streptocerca - Mansonella perstans - Mansonella ozzardi

• Wolbachia Endosymbiont: - Found in all stages of Brugia, Wuchereria, Mansonella, and Onchocerca species. - Targeted by antifilarial chemotherapy to eliminate the symbiont.

• Life Cycle & Pathogenesis: - Microfilariae circulate in blood or skin; ingested by vectors and develop into infective larvae over 1–2 weeks. - Adult worms can live for years; microfilariae survive 3–36 months. - Chronic infections often result in delayed clinical manifestations.

1.1 Abdominal Angiostrongyliasis¶

Caused by Angiostrongylus costaricensis, primarily affecting children in Latin America.

• Transmission: Ingestion of contaminated vegetation containing infective larvae from slugs/snails. • Pathogenesis: Larvae migrate to mesenteric arterioles, causing granulomatous inflammation and potential bowel infarction. • Clinical Features: Abdominal pain (right iliac fossa), fever, vomiting, palpable mass; often mimics appendicitis. • Diagnosis: Histology of tissue or identification of peanut-shaped eggs in stool. Serologic tests are currently unavailable. • Treatment: - Albendazole: 400 mg BID × 10 days. - Mebendazole: 500 mg/day × 20 days. - Surgical resection for severe cases.

1.2 Lymphatic Filariasis Overview¶

Caused by Wuchereria bancrofti, Brugia malayi, or Brugia timori.

• Geographic Distribution: - W. bancrofti: Cosmopolitan (Asia, Africa, Americas). - B. malayi: Southeast Asia, India. - B. timori: Indonesia.

• Vectors: Culex, Anopheles, Aedes (mosquitoes); Mansonia; Coquillettidia.

• Pathology: Inflammation from adult worms leads to lymphatic dilation, valve incompetence, fibrosis, and lymphedema.

2. EPIDEMIOLOGY¶

• Global Prevalence: ~170 million infections. • Lymphatic Filariasis: 51 million cases (W. bancrofti dominant). • Onchocerciasis: 37 million cases in 31 countries (Africa, Venezuela, Brazil, Yemen). • Loiasis: West/Central Africa (L. loa). • Mansonella species: M. streptocerca (Africa), M. perstans (Africa/South America), M. ozzardi (Americas).

3. ETIOLOGY & PATHOPHYSIOLOGY¶

• Lymphatic Filariasis: - Adult worms cause inflammatory damage → lymphatic dilation, valve incompetence, and fibrosis. - Clinical outcomes: Lymphedema, brawny edema, hyperkeratosis, and chyluria (from retroperitoneal obstruction).

• Onchocerciasis: - Microfilariae-induced hypersensitivity → skin atrophy, corneal scarring, and optic atrophy. - Subcutaneous nodules (onchocercomata) contain adult worms. - Lymph nodes: Inguinal/femoral enlargement ('hanging groin').

• Loiasis: - Calabar swellings: Hypersensitivity to adult worm antigens. - Systemic: Headache, arthralgia, hepatomegaly, pruritus, eosinophilia.

• Abdominal Angiostrongyliasis: - Caused by Angiostrongylus costaricensis. - Pathogenesis: Larvae migrate to mesenteric arterioles → granulomatous inflammation and potential bowel infarction.

4. CLINICAL FEATURES¶

• Lymphatic Filariasis: - Asymptomatic microfilaremia. - Hydrocele (W. bancrofti). - Acute adenolymphangitis (ADL): High fever, lymphadenopathy, retrograde lymphangitis, transient edema. - Brugian filariasis: Local abscess formation and rupture. - Dermatolymphangioadenitis (DLA): Fever, chills, myalgia, erythematous plaques with vesicles/ulcers; often misdiagnosed as cellulitis. - Chronic Lymphatic Disease: Progression from pitting edema → brawny edema, hyperkeratosis, fissures.

• Onchocerciasis: - Skin: Generalized papular eruption, sowdah (hyperpigmented dermatitis), skin atrophy. - Eye: Punctate keratitis ('snowflake' opacities), sclerosing keratitis (leading to blindness), anterior uveitis.

• Loiasis: - Calabar swellings (evanescent angioedema). - Subconjunctival migration of adult worms. - Systemic: Eosinophilia, pruritus.

• Abdominal Angiostrongyliasis: - Presentation: Abdominal pain (right iliac fossa), fever, vomiting, palpable mass; mimics appendicitis.

5. DIFFERENTIAL DIAGNOSIS¶

• Lymphatic filariasis: - Lymphedema (distinguish from lymphoma). - Hydrocele (distinguish from testicular torsion). - Chyluria (distinguish from tuberculosis).

• Onchocerciasis: - Pruritus (scabies, drug reactions). - Corneal opacities (trachoma, leprosy).

• Loiasis: - Calabar swellings (angioedema, hereditary angioedema).

6. INVESTIGATIONS & DIAGNOSIS¶

Lymphatic Filariasis:
Step 1: Microfilariae detection in blood (Timing: Nocturnal for W. bancrofti; Subperiodic for B. malayi).
Step 2: Circulating antigen detection (Specificity >98%).
Step 3: Ultrasound to identify 'filarial dance sign' (adult worms in lymphatics).
Onchocerciasis:
Step 1: Skin snips or blood smear for microfilariae.
Step 2: Ophthalmologic exam (slit lamp) for corneal opacities/retinal lesions.
Loiasis:
Step 1: Blood smear for microfilariae (non-periodic).
Step 2: Subconjunctival worm visualization.
Abdominal Angiostrongyliasis:
Step 1: Histology of tissue or stool exam to identify peanut-shaped eggs.
Note: Serologic tests are unavailable.

6.1 Diagnostic Criteria and Tests¶

• Lymphatic filariasis: Microfilariae in blood (timing-specific), antigen detection, ultrasound. • Onchocerciasis: Skin snip/microfilariae in blood, slit lamp exam for ocular lesions. • Loiasis: Blood smear for microfilariae, subconjunctival worm visualization.

7. MANAGEMENT & TREATMENT¶

Lymphatic Filariasis:
Active disease: Diethylcarbamazine (DEC) 6 mg/kg daily imes 12 days.
Mass Drug Administration (MDA): Ivermectin + albendazole (annual distribution).
Onchocerciasis:
Standard treatment: Ivermectin 150–200 μg/kg every 6–12 months.
Critical Safety Check: Contraindicated in Loa loa co-endemic areas if microfilaremia >30,000/mL (risk of severe encephalopathy).
Loiasis:
Tropical pulmonary eosinophilia (TPE): DEC 4–6 mg/kg for 14 days.
Abdominal Angiostrongyliasis:
Option A: Albendazole 400 mg BID imes 10 days.
Option B: Mebendazole 500 mg/day imes 20 days.
Surgical intervention for severe cases.
Mansonella Treatment:
Ivermectin or Doxycycline (to target Wolbachia).
Public Health Strategy:
Mass drug administration (MDA) with DEC, ivermectin, and albendazole.
Vector control: Insecticide-treated nets, environmental management.

7.1 Lymphatic Filariasis Treatment¶

• DEC: 6 mg/kg daily imes 12 days. • Ivermectin + albendazole for MDA (annual distribution).

7.2 Onchocerciasis Treatment¶

• Ivermectin: 150–200 μg/kg every 6–12 months. • Contraindicated in Loa loa co-endemic areas (>30,000 microfilariae/mL).

7.3 Loiasis Treatment¶

• DEC: 4–6 mg/kg imes 14 days for TPE. • Albendazole: 400 mg BID imes 10 days for abdominal angiostrongyliasis.

7.4 Mansonella Treatment¶

• Ivermectin or Doxycycline (for Wolbachia elimination).

8. PROGNOSIS & COMPLICATIONS¶

• Lymphatic filariasis: Chronic disability from elephantiasis, hydrocele, chyluria. • Onchocerciasis: Blindness (sclerosing keratitis), skin atrophy, dermatitis. • Loiasis: Encephalopathy in Loa loa co-infection, protein-losing enteropathy. • Abdominal Angiostrongyliasis: Bowel infarction from granulomatous inflammation.

9. SPECIAL CONSIDERATIONS¶

• Prevention: - Vector control (insecticide-treated nets). - MDA programs with DEC/ivermectin/albendazole.

• Travelers: - Consider filarial infections in endemic regions if presenting with lymphedema, eosinophilia, or Calabar swellings.

9.1 Prevention and Control¶

• Mass drug administration (MDA) with DEC/ivermectin/albendazole. • Vector control: Insecticide-treated nets, environmental management. • Surveillance for microfilariae and antigenemia.

10. KEY PEARLS & CLINICAL TRAPS¶

• Critical Contraindications: - DEC is contraindicated in patients with high Loa loa microfilaremia (>30,000 microfilariae/mL) due to risk of encephalopathy. - Ivermectin is also contraindicated in Loa loa co-endemic areas for the same reason.

• Clinical Traps: - Do not mistake Dermatolymphangioadenitis (DLA) for cellulitis. - Underestimate chronic lymphatic damage in endemic populations.

• Diagnostic Keys: - 'Filarial dance sign' on ultrasound confirms adult worms in lymphatics. - Peanut-shaped eggs are pathognomonic for Angiostrongyliasis.

Reference Tables¶

TABLE 240-1 Characteristics of the Filariae ORGANISM Wuchereria bancrofti¶

Harrison's 22e, p.1820

ORGANISM	PERIODICITY	DISTRIBUTION	VECTOR	LOCATION OF ADULT	MICROFILARIAL LOCATION	SHEATH
Wuchereria bancrofti	Nocturnal	Cosmopolitan areas worldwide, including South America, Africa, southern Asia, Papua New Guinea, China, Indonesia	Culex, Anopheles (mosquitoes)	Lymphatic tissue	Blood	+
	Subperiodic	Eastern Pacific	Aedes (mosquitoes)	Lymphatic tissue	Blood
Brugia malayi	Nocturnal	Southeast Asia, Indonesia, India	Mansonia, Anopheles (mosquitoes)	Lymphatic tissue	Blood	+
	Subperiodic	Indonesia, Southeast Asia	Coquillettidia, Mansonia (mosquitoes)	Lymphatic tissue	Blood
Brugia timori	Nocturnal	Indonesia	Anopheles (mosquitoes)	Lymphatic tissue	Blood	+
	Diurnal	West and Central Africa	Chrysops (deerflies)	Subcutaneous tissue	Blood
Onchocerca volvulus	None	South and Central America, Africa	Simulium (blackflies)	Subcutaneous tissue	Skin, eye	–
	None	South and Central America	Culicoides (midges)	Undetermined site	Blood
	None	Caribbean	Simulium (blackflies)	Undetermined site	Blood	–
	None	South and Central America, Africa	Culicoides (midges)	Body cavities, mesentery, perirenal tissue	Blood
Mansonella streptocerca	None	West and Central Africa	Culicoides (midges)	Subcutaneous tissue	Skin	–