Question
What are the clinical features, laboratory diagnosis and treatment of filariasis
Answer
Filariasis (lymphatic filariasis), caused by Wuchereria bancrofti (predominantly) and Brugia malayi/B. timori, is transmitted by mosquito vectors (Culex for W. bancrofti; Mansonia/Anopheles for Brugia), with adult worms residing in lymphatic vessels/nodes.
Clinical features:
- Asymptomatic microfilaraemia — common, often with no overt clinical disease despite circulating microfilariae.
- Acute adenolymphangitis — recurrent episodes of fever with painful, tender, inflamed lymphatics/lymph nodes, often triggered by secondary bacterial infection.
- Chronic manifestations — lymphoedema and elephantiasis (typically lower limbs), and in men, hydrocele and scrotal/genital lymphoedema.
- Tropical Pulmonary Eosinophilia (TPE) — a hypersensitivity syndrome causing paroxysmal nocturnal cough, wheeze, and marked eosinophilia, without demonstrable blood microfilaraemia (“occult” filariasis).
Laboratory diagnosis:
- Peripheral blood smear microscopy — thick smear (Giemsa) for microfilariae, timed to nocturnal periodicity (blood collection around midnight) for most W. bancrofti strains; concentration techniques (Knott’s method, membrane filtration) improve sensitivity.
- Circulating filarial antigen (CFA) detection — immunochromatographic card test, detects adult worm antigen, not subject to periodicity constraints.
- Ultrasonography — can visualize live, motile adult worms within dilated lymphatics (“filarial dance sign”).
- Serology — supportive but limited specificity due to cross-reactivity with other helminths.
Treatment: Diethylcarbamazine (DEC) — the mainstay antifilarial drug, active against both microfilariae and (to a lesser extent) adult worms; albendazole is often combined with DEC (or ivermectin, in onchocerciasis-co-endemic areas) for mass drug administration programmes; management of chronic lymphoedema (limb hygiene, compression, elevation) and hydrocelectomy for hydrocele are important adjuncts for established chronic disease, since antifilarial drugs cannot reverse existing lymphatic damage.
Public health: targeted for global elimination through the WHO’s Global Programme to Eliminate Lymphatic Filariasis, using mass drug administration alongside vector control.