Filaria is caused by the parasite known as Wuchereria bancrofti in most parts of India. The infection is common in both urban and rural areas in India. Culex mosquito is the vector that transmits the disease from one person to other. The adult parasite produces small, immature larvae known as microfilariae and one adult parasite can produce millions of microfilariae in it’s life period of 4-6 years. The microfilariae circulate in the peripheral blood usually in the night. The disease is transmitted by bite of an infected Culex mosquito.
When the culex mosquito bites an infected person the microfilariae enter the body of a mosquito. In the mosquito microfilariae takes about 7-21 days to develop. After this when the mosquito bites a healthy person it transmits the disease.
Another parasite that causes filariasis is Brugia malayi. It is transmitted by the vector Mansonia (Mansonioides) annulifera. Brugia malayi infection is mainly found in rural areas. Microfilariae of both W bancrofti and B malayi infections exhibit nocturnal periodicity.
Filariasis develops usually after many mosquito bites over several months to year. The risk of infection is higher in people living for a long time in areas where filariasis is common. The risk of infection in short-term tourists to filarial endemic areas is very low.