randomized trial of doxycycline, an antibiotic, for Mansonella perstans infection. This resulted in a dramatic and sustained decrease in microfilarial levels: they decreased to 23% of pretreatment levels at 6 m after treatment and to 0% of pretreatment levels at 12 m after treatment. In addition, doxycycline has been shown to have macrofilaricidal activity, which is unique among the drugs for filariasis. However, in some areas, such as Gabon and Uganda, Wolbachia endosymbionts have not been detected in the microfilariae of M. perstans. This suggests some geographic isolates of M. perstans may have lost (or gained) the endosymbiont. This presents a controversial argument for the use of doxycycline as treatment of filarial infections. On one hand, doxycycline has been shown to be one of the only successful treatments for M. perstans, and could facilitate the eradication of filarial parasites. However, some scientists argue that the treatment of filariasis with doxycycline may select worms that will have already integrated Wolbachia genes into their genome, which could potentially have unforeseen consequences. Such lateral gene transfer has occurred in various geographic isolates of B. malayi, in which a fraction of the Wolbachia endosybmiont genome is integrated into the chromosome of its nematode host (the parasite). When this integration occurs, Wolbachia can no longer be targeted as means for treatment for filariasis. Combination regimens Combination treatments consisting of DEC plus mebendazole, or ivermectin and albendazole, have been shown to result in a highly significant fall in microfilariae. Other studies have challenged these findings, suggesting the combination treatment of ivermectin and albendazole does not significantly reduce microfilariae levels more than a single treatment regimen. Epidemiology M. perstans is found in tropical Africa, central and eastern South America, Central America, and the Caribbean. The parasite is widespread in many parts of sub-Saharan Africa. Infections have been reported from 33 countries in this region. In certain locations, extremely high proportions of the inhabitants show signs of infection. It often occurs among poor populations living in rural villages. M. perstans is also found in the Americas in Venezuela, Trinidad, Guyana, Suriname, northern Argentina and the Amazon basin. This parasite does not occur in Asia. It also does not occur in the most northern and southern regions of Africa. A recent review of M. perstans in Africa states that about 114 million people are infected with this parasite in Africa today. Public health and prevention strategies The ongoing large-scale