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Parasites and Vectors

, 6:289

Elimination of parasitic infections

Abstract

BackgroundOnchocerciasis is caused by Onchocerca volvulus and transmitted by Simulium species black flies. In the Americas, the infection has been previously described in 13 discrete regional foci distributed among six countries Brazil, Colombia, Ecuador, Guatemala, Mexico and Venezuela where more than 370,000 people are currently considered at risk. Since 2001, disease control in Venezuela has relied on the mass drug administration to the at-risk communities. This report provides empirical evidence of interruption of Onchocerca volvulus transmission by Simulium metallicum in 510 endemic communities from two Northern foci of Venezuela, after 10–12 years of 6-monthly Mectizan® ivermectin treatment to all the eligible residents.

MethodsIn-depth entomologic and epidemiologic surveys were serially conducted from 2001–2012 in selected sentinel and extra-sentinel communities from the North-central NC and North-east NE onchocerciasis foci of Venezuela in order to monitor the impact of ivermectin treatment.

ResultsFrom 2007–2009, entomological indicators in both foci confirmed that 0 out of 112,637 S. metallicum females examined by PCR contained L3 infection in insect heads. The upper bound of the 95% confidence intervals of the infective rate of the vector reached values below 1% by 2009 NC and 2012 NE. Additionally, after 14 NC and 22 NE rounds of treatment, the seasonal transmission potential ±UL CIs of S. metallicum was under the critical threshold of 20 L3 per person per season. Serological analysis in school children < 15 years-old demonstrated that 0 out of 6,590 individuals were harboring antibodies to Ov-16. Finally, epidemiological surveys made during 2010 NC and 2012 NE showed no evidence of microfilariae in the skin and eyes of the population.

ConclusionsThese results meet the WHO criteria for absence of parasite transmission and disease morbidity in these endemic areas which represent 91% of the population previously at-risk in the country. Consequently, the two Northern foci are currently under post-treatment onchocerciasis surveillance status in Venezuela.

KeywordsOnchocerciasis Simulium metallicum Interruption Ivermectin Venezuela Electronic supplementary materialThe online version of this article doi:10.1186-1756-3305-6-289 contains supplementary material, which is available to authorized users.

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