Macrofilaricides and onchocerciasis control, mathematical modelling of the prospects for elimination

Abstract

BackgroundIn most endemic parts of the world, onchocerciasis (river blindness) control relies, or will soon rely, exclusively on mass treatment with the microfilaricide ivermectin. Worldwide eradication of the parasite by means of this drug is unlikely. Macrofilaricidal drugs are currently being developed for human use.MethodsWe used ONCHOSIM, a microsimulation mathematical model of the dynamics of onchocerciasis transmission, to explore the potentials of a hypothetical macrofilaricidal drug for the elimination of onchocerciasis under different epidemiological conditions, as characterized by previous intervention strategies, vectorial capacity and levels of coverage.ResultsWith a high vector biting rate and poor coverage, a very effective macrofilaricide would appear to have a substantially higher potential for achieving elimination of the parasite than does ivermectin.ConclusionsMacrofilaricides have a substantially higher potential for achieving onchocerciasis elimination than ivermectin, but high coverage levels are still key. When these drugs become available, onchocerciasis elimination strategies should be reconsidered. In view of the impact of control efforts preceding the introduction of macrofilaricides on the success of elimination, it is important to sustain current control efforts.

Antibiotic Chemotherapy of Onchocerciasis: In a Bovine Model, Killing of Adult Parasites Requires a Sustained Depletion of Endosymbiotic Bacteria (WolbachiaSpecies)

“…Our results suggest that macrofilaricidal activity against O. volvulus may be achieved by the administration of tetracyclines intermittently at a lower total dose but over a longer period, such as 3-5 day treatments monthly for 6 months. With clear evidence emerging that, in Africa, O. volvulus cannot be eliminated with the administration of ivermectin alone [4], in conjunction with modeling studies that have shown the potential of macrofilaricidal regimens to achieve elimination [36] and increasing concerns about the development of ivermectin resistance [37], the thorough research evaluation of antibiotics in a macrofilaricidal context is imperative. An important potential application would be in foci of human infection, in which ivermectin insusceptibility is a problem, and its proliferation into other areas must be prevented [38].…”

Measuring the global burden of disease and epidemiological transitions: 2002–2030

“…ONCHOCERCIASIS Prevalence of blindness from onchocerciasis was re-estimated from the available results of prevalence studies and overall blindness surveys, taking into account the declining trends in prevalence and the coverage and duration of onchocerciasis-control programmes (Alley et al, 2001;Richards et al, 2001;Shibuya and Ezzati, 2003). LEPROSY Regional incidences and prevalences of leprosy were based on case reporting and the results of surveillance by 120 of the WHO's member states (Stein, 2002a;WHO, 2002c).…”

The Role of Endosymbiotic Wolbachia Bacteria in the Pathogenesis of River Blindness

“…It rapidly reduces the number of skin microfilariae, but depletes them only for a few months, after which they reappear at amounts of 20% or more of pretreatment levels within a year [111]. This seems to be sufficient for transmission to continue [112].…”