**1. Introduction**

There are eight parasites responsible for filarial infections. Three parasites *Wuchereria bancrofti* (Cobbold 1877), *Brugia malayi* (Brug 1927) and *B. timori* (Partono et al. 1977) are responsible for lymphatic filariasis (LF) that impairs the lymphatic system leading to severe organ deformities leading to social stigma [1–3]. In India, the first two species *W. bancrofti* and *B. malayi* are present. *W. bancrofti* contributes 99.4% of the total burden. It is a roundworm nematode parasitic helminthiasis group of diseases under the Filarioidea type of infection. The main affected organs are legs and genitals causing 'elephantiasis' and hydrocele in males and breast filariasis in females followed by relentless disability causing social stigma. In Indian local language the disease is known as 'Hathipaon'. In India, LF is the second most vector-borne disease after malaria and globally ranks third after malaria and tuberculosis. The World Health Organization (WHO) estimated that LF is found in 81 tropical and subtropical countries with 120 million infected cases and with one billion people at risk; 947 million people are threatened, whereas 40 million people are disfigured by this infection. Four countries India, Indonesia,

Bangladesh (all Asian countries) and Nigeria (Africa) contribute about 70% of the LF infection in the world [4].

In the sixth century BC in his book, *Susruta Samhita*, Susruta mentioned this disease. In the seventh century AD in his memoir, *Madhava Nidhana*, Madhavarakara first described the signs and symptoms of this disease. In 1709, Clarke described 'Malabar legs' from Cochin which is synonymous with elephantiasis. In 1872 in Calcutta (now Kolkata), Lewis first described the microfilariae (Mf) in human blood [5].

LF is distributed in economically challenged countries. *W. bancrofti* is the most predominant species of human filariasis. It was recognized primarily as an urban disease which does not have animal reservoirs. Later it is reported from rural areas also. The parasites develop only in humans and in mosquitoes. But the adult worms may survive for 8–10 years and produce huge numbers of Mf from time to time. This is actually the real challenge in containing the disease.
