The purpose of this study is to detect lymphatic filariasis in blood samples to determine whether the recently concluded Program to Eliminate Lymphatic Filariasis has been successful in controlling lymphatic filariasis (LF) in areas of Egypt. The Research and Training Center on Vectors of Diseases (RTC) at Ain Shams University in Cairo, Egypt, will be the central site for data management and laboratory studies. Field sites (localities for village and school surveys) are 44 villages and small towns in 27 Districts and 7 governorates in the Nile river delta and in Giza. These localities are chosen based on inclusion in the Egyptian National Program to Eliminate Lymphatic Filariasis (PELF). Other localities will be chosen because of proximity to known endemic localities or a past history of filariasis endemicity. The primary study objective is to conduct population-based field studies to address key questions faced during late stages of programs for elimination of lymphatic filariasis (ELF). The investigators will test the hypothesis that filariasis has been eliminated in Egypt by 5 rounds of Mass Drug Administration (MDA) and attempt to answer the following questions: (1) Has LF been eliminated in localities included in the Egyptian National ELF Program? The investigators will study 44 localities (22 per year in alternate years). (2) What characteristics in endemic communities affect the likelihood of success or failure for ELF programs? The goal here is to identify key characteristics shared by localities that achieved elimination. (3) Are there significant foci of infection in localities that were not included in the Egyptian National PELF? The investigators will screen 20 new localities per year for the first 3 years of the project. The investigators will conduct a cohort study of the natural history of filarial antigenemia in treated populations. This study will test two hypotheses: (a) Filarial antigenemia without microfilaremia following completion of a MDA program with diethylcarbamazine and albendazole is of very little parasitological significance. That is to say, these people are unlikely to develop levels of microfilaremia that support filariasis transmission. (b) Following completion of a MDA program, filarial antigen levels in amicrofilaremic subjects will decline over time and disappear without further treatment. The investigators will assess the value of advanced diagnostic methods for detecting foci of continued transmission and for early detection of resurgent transmission. The duration of this study is 5 years, and approximately 23,500 people will participate per year. Most participants will be studied only once in cross-sectional surveys. The study population will include females and males over 6 years of age who live in areas of Egypt that are known to have been endemic or are now suspected to be endemic for bancroftian filariasis. Subject selection will not be based on health status. A subset of people, approximately 120, will be followed in a cohort study for 2 years.