Question
Lymphatic filariasis.
Answer
Lymphatic filariasis is caused by Wuchereria bancrofti (predominantly) and Brugia malayi/B. timori, transmitted by mosquito vectors (Culex quinquefasciatus for W. bancrofti; Mansonia/Anopheles for Brugia), with adult worms residing in lymphatic vessels/nodes.
Pathogenesis: adult worms cause lymphatic dilatation, endothelial proliferation, and progressive lymphatic dysfunction, both from direct physical presence and from the host’s chronic inflammatory response to dead/dying worms; secondary bacterial infection worsens tissue damage, driving progression to chronic lymphoedema/elephantiasis.
Clinical features: asymptomatic microfilaraemia; acute adenolymphangitis (recurrent fever with painful, inflamed lymphatics); chronic lymphoedema and elephantiasis (typically lower limbs), and in men, hydrocele; Tropical Pulmonary Eosinophilia (a hypersensitivity syndrome without demonstrable microfilaraemia).
Laboratory diagnosis:
- Peripheral blood smear microscopy — thick smear (Giemsa) for microfilariae, timed to nocturnal periodicity (midnight blood collection); concentration techniques (Knott’s method, membrane filtration).
- Circulating filarial antigen (CFA) detection — immunochromatographic test, not periodicity-dependent.
- Ultrasonography — visualizes live adult worms (“filarial dance sign”).
Treatment: Diethylcarbamazine (DEC), often with albendazole; management of chronic lymphoedema and hydrocelectomy for established disease.
Public health significance: targeted for global elimination through the WHO’s Global Programme to Eliminate Lymphatic Filariasis, using mass drug administration alongside vector control.