 Eligibility for the cohort study: Subjects in household surveys with positive immunochromotography test, filarial antigen tests, and negative microfilaria thick blood smears and who took diethylcarbamazine and albendazole during the Egyptian Program to Eliminate Lymphatic Filariasis will be invited to participate in the study. Subjects must be residents of localities that have met the Basic Elimination criterion community microfilaria prevalence by thick smear less than 1 or antigen prevalence rate less than 2. Consenting subjects will be screened further by testing a sample of venous blood collected after 9 p.m. for microfilaremia by membrane filtration and by performing an ELISA to quantitate filarial antigenemia in serum. Eligible subjects will have no microfilaremia by smear and antigen levels 20 ngml. 