Interruption of Onchocerca volvulus transmission in Northern Venezuela.

Jacinto Convit,Rafael Borges,Alfredo Domínguez-Vázquez,María E Grillet,Vimerca Olivero,Hortencia Frontado,Harland Schuler

doi:10.1186/1756-3305-6-289

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.

Highlights

Onchocerciasis is caused by Onchocerca volvulus and transmitted by Simulium species
We have reported evidences of the local interruption of O. volvulus transmission by Simulium metallicum in 510 endemic communities localized in Northern Venezuela after 10–12 continuous years of 6-monthly ivermectin treatment
The results presented here indicate that onchocerciasis infection no longer poses a significant public health risk in this northern endemic area in Venezuela

Summary

Introduction

Onchocerciasis is caused by Onchocerca volvulus and transmitted by Simulium species (black flies). In the Americas, thirteen onchocerciasis foci have been described in Brazil, Colombia, Ecuador, Guatemala, Mexico and Venezuela, where about 379,234 persons were considered at risk of infection as of 2013 [1] In this region, several ecological settings are associated with distinct but welladapted Onchocerca–Simulium complexes which show various parasite transmission intensities, degrees of infection severity, clinical manifestations, and epidemiological patterns. The southern onchocerciasis Amazonian focus is confined to the rainforest of the Upper Orinoco River region, affecting about 10,390 people [4] from the indigenous Yanomami population [8,9] In this second endemic area, S. guianense s.l. Wise, S. incrustatum Lutz, and S. oyapockense s.l. Floch and Abonnenc are the vectors [10,11,12]

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