Basic science of lymphatic filariasis

Filarial disease, transmitted from person-to-person by mosquitoes, principally affects people in tropical and sub-tropical areas. One hundred and twenty million people in at least 80 nations of the world have lymphatic filariasis. One billion people are at risk of getting infected. Ninety percent of these infections are caused by Wuchereria bancrofti , and most of the remainder by Brugia malayi. For W. bancrofti , humans are the exclusive host. The major vectors for W. bancrofti are culicine mosquitoes in most urban and semiurban areas, anophelines in the more rural areas. Larvae in the blood of human hosts are ingested when the insect vectors feed. Within the vector, the microfilarias migrate to specific sites and develop from first-stage larvae into infective third-stage larvae. The vector transmits the infective larvae into a human host when feeding. Mosquitoes deposit the larvae on the host skin adjacent to the puncture site and the third stage larval (L3) parasites migrate through the venous system and lungs to eventually take up residence in the lymphatics. There they form nests occupied by male and female worms, and produce the first stage larvae or microfilariae by viviparous reproduction These larvae migrate from the lymphatics to the peripheral blood where mosquitoes ingest them. The filarial disease has protean manifestaions in the form of chronic, acute and ′asymptomatic′ presentations as well as a number of syndromes associated with these infections that may or may or not be caused by the parasites