Selective primary health care: strategies for the control of disease in the developing world. VII. Filariasis.

At least 250 million people throughout the world are infected with filariae, and the number of such persons is increasing. Three species infect humans: Wuchereria bancrofti, Brugia malayi, and Brugia timori. The peak of microfilarial density in the blood usually occurs nocturnally. Transmission of filariasis is remarkably inefficient. In an endemic area, approximately 100,000 mosquito bites yearly are required for production of each new case of microfilaremia. Only a small proportion of those infected suffer any ill effects from these worms. Clinical filariasis can present with acute inflammation such as lymphangitis and lymphadenitis and with chronic lymphatic obstruction such as hydrocele and lymphedema of the limbs. Measures available for potential control include the widespread usage of mosquito nets, vector control, and chemotherapy with diethylcarbamazine. Unfortunately, the efficacy of the first of these is untested and the latter two are inadequate. More research is required on vector control, assessment of new drugs, and the development of vaccines.