Effect of MDA on lymphedema. There has been evidence for a protective association between intake of anti- filarial drugs and the occurrence of lymphedema in endemic populations. A randomized trial comparing the efficacy of DEC + ivermectin with that of DEC alone in Papua New Guinea [78] found a significant decrease in the frequency of lymphedema after 4 annual MDA’s among both treatment groups. Findings from the study showed that the proportion of male subjects with advanced hydrocele was 15% before the trial began and 5% one year after the fourth treatment (P<0.001). The frequency of lymphedema of the legs was 5% pre-treatment and decreased to 4% one year following the 4th round of MDA (P=0.04). Although this is a small change, it was statistically significant. For a chronic illness like lymphedema, it would be unexpected to see a large percent change in the prevalence of any lymphedema over the course of 5 years. In a separate analysis of only individuals who had pre-existing lymphedema at the beginning of the trial, 87% of men who had advanced hydrocele and 69% of those with lymphedema of the legs at the beginning of the trial no longer had clinical signs of the disease by the end. The authors of the trial speculate that mass treatment with anti-filarial drugs decreases exposure to infective 3rd stage larvae, and this in turn diminishes the intensity of inflammatory responses to newly inoculated W. bancrofti or to the Wolbachia endosymbiont. Several other studies have found a similar relationship between anti-filarial drugs and lymphedema. An early study of two rounds of DEC treatment in Indonesia found that nearly all of the patients with lymphedema post-treatment had complete regression of swelling within three years [79]. Those with elephantiasis regressed more slowly, taking two to four years for most. In Tanzania, Meyrowitsch showed that 1 annual and 2 semi- annual DEC treatments resulted in a decrease in the frequency of hydroceles [80]. One year after the start of treatment, 57.9% of males with hydrocele who took 1 annual dose of DEC showed improvement either through reduction in size or complete disappearance. Among men who took 2 semi-annual doses of DEC, 68.2% showed improvement. No such effect was observed on leg elephantiasis.
