Filariasis-free Sri Lanka

Lymphatic filariasis (LF) is caused by a variety of filarial parasites of which 2 are found in Sri Lanka viz. Wuchereria bancrofti and Brugia malayi. Of the two, Brugia malayi is more widely adapted to animal hosts other than humans. Adult worms are very small and lodge in the lymphatic system living for around 4-6 years. They produce thousands of immature microfilariae which reach the peripheral blood stream nocturnally and are ingested by mosquitoes mainly belonging to the Culex species. In Sri Lanka, Culex quinquefasciatus is the sole vector responsible for the spread of filariasis, transmitting the microfilariae from person to person. Microfilariae ingested by Culex quinquefasciatus change into larvae which are deposited on the surface of the human skin during a blood meal. The larvae penetrate the skin, find their way into the lymphatic vessels and become adult males and females in 6-12 months. Culex quinquefasciatus mosquito breeds in polluted and stagnant collections of water which are plentiful in urban areas. Common breeding sites include blocked drains, pit latrines and damaged septic tanks. Only a proportion of persons infected with filarial parasites develop clinical symptoms. Acute clinical manifestations of LF include episodic attacks of adeno-lymphangitis whilst chronic clinical manifestations include chronic lymphoedema or elephantiasis, hydrocoele and chyluria.