Drug distribution. A volunteer health worker distributes anti-filarial drugs as part of a programme of mass drug administration with DEC (diethylcarbamazine citrate). This drug is used to cure and prevent spread of filariasis, a group of diseases caused by parasitic worms which invade the lymphatic system, the skin or the eye. The worm larvae are spread by blood-sucking insects. In lymphatic filariasis the worms cause inflammation of the lymph vessels which can result in accumulation of fluid and enormous enlargement of parts of the body (elephantiasis). Photographed in India.