The pathogenesis of filarial lymphedema: is it the worm or is it the host?

Our understanding of the pathogenesis of filarial lymphedema, although evolving, is still limited. Recurrent bacterial infections play a major role in the progression of lymphedema to elephantiasis, but the host and parasite factors that trigger disease development are not known. Field studies in Haiti show that lymphedema and host responses to parasite antigens cluster in families, consistent with the hypothesis that host genes influence lymphedema susceptibility. The recent recognition that filarial parasites harbor the endosymbiotic bacteria, Wolbachia, also raises questions about the potential contribution of the inflammatory response to Wolbachia antigens to lymphedema development. In this review, we discuss potential risk factors for lymphedema and try to integrate these in a model of pathogenesis.