Treatment Challenges
  The methods currently employed to combat Onchcocerciasis have driven successful public health efforts for years, but there remain many drawbacks and challenges to ultimate eradication. Coverage is often too low within a population to stop transmission and frequently the parasite is reintroduced into controlled areas by migration of infected individuals. There is also growing evidence that Ivermectin may not be as effective of a public health treatment as originally believed. The most important inadequacies of Ivermectin include:  
  • Insufficient reduction in microfilaria density: Ivermectin quickly reduces microfilaremia but within a year it may increase again. While microfilarias remains lower than pre-treatment levels it may not be low enough to stop transmission. There is evidence of continued local transmission in Africa after 10-12 years of mass ivermectin treatment.
  • Adult worms: Ivermectin is only a microfilaricide. The adult worms live greater than 14 years, thus treatment must continue throughout their long life course. The recent conference on Onchocerciasis eradication concluded that at least 65% coverage for 35 years would be necessary for elimination
  • Drug resistance: Parasitic helminthes of animals have been observed to develop resistance to Ivermectin. Treatment causes loss of polymorphism at several specific loci in the genome. Human treatment for O.volvulus has also resulted in some losses of polymorphism suggesting a mechanism for future resistance

In light of these complications, there has been an emerging demand for complementary tools to combat Onchcocerciasis. New chemotherapeutic treatments are needed that will have a stronger and more sustained impact on microfilaria and that target the adult worms. Alternate treatments are especially important to have available in case resistance to ivermectin develops in the near future. In recent years, much research for alternate treatments has focused on the use of tetracycline antibiotics that target the endosymbiotic bacteria of the genus Wolbachia.
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