The symbiosis of filarial nematodes and intracellular Wolbachia bacteria has recently been exploited as a target for antibiotic therapy of filariasis. Antibiotic treatment of filarial nematodes results in sterility and inhibits larval development and adult worm viability. In the first trial on human onchocerciasis depletion of bacteria following treatment with doxycycline resulted in a complete and long-term block of embryogenesis. Bacteria are unable to repopulate nematode tissues up to 18 months after depletion, suggesting these effects may be permanent. Following ivermectin treatment, individuals given antibiotic therapy showed sustained reductions in skin microfilariae, with the majority of people remaining microfilarial negative 12-18 months after treatment. Since Wolbachia also contribute to the inflammatory pathogenesis of filarial disease, antibiotic therapy could, in addition to effects on worm fertility or viability, prevent the onset or development of filarial pathology.