Elimination of Onchocerciasis from Mexico

PLoS Negl Trop Dis. 2015 Jul 10;9(7):e0003922. doi: 10.1371/journal.pntd.0003922. eCollection 2015.

Abstract

Background: Mexico is one of the six countries formerly endemic for onchocerciasis in Latin America. Transmission has been interrupted in the three endemic foci of that country and mass drug distribution has ceased. Three years after mass drug distribution ended, post-treatment surveillance (PTS) surveys were undertaken which employed entomological indicators to check for transmission recrudescence.

Methodology/principal findings: In-depth entomologic assessments were performed in 18 communities in the three endemic foci of Mexico. None of the 108,212 Simulium ochraceum s.l. collected from the three foci were found to contain parasite DNA when tested by polymerase chain reaction-enzyme-linked immunosorbent assay (PCR-ELISA), resulting in a maximum upper bound of the 95% confidence interval (95%-ULCI) of the infective rate in the vectors of 0.035/2,000 flies examined. This is an order of magnitude below the threshold of a 95%-ULCI of less than one infective fly per 2,000 flies tested, the current entomological criterion for interruption of transmission developed by the international community. The point estimate of seasonal transmission potential (STP) was zero, and the upper bound of the 95% confidence interval for the STP ranged from 1.2 to 1.7 L3/person/season in the different foci. This value is below all previous estimates for the minimum transmission potential required to maintain the parasite population.

Conclusions/significance: The results from the in-depth entomological post treatment surveillance surveys strongly suggest that transmission has not resumed in the three foci of Mexico during the three years since the last distribution of ivermectin occurred; it was concluded that transmission remains undetectable without intervention, and Onchocerca volvulus has been eliminated from Mexico.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Anthelmintics / administration & dosage
  • Female
  • Humans
  • Insect Vectors / parasitology
  • Insect Vectors / physiology
  • Ivermectin / administration & dosage
  • Male
  • Mexico / epidemiology
  • Onchocerca volvulus / genetics
  • Onchocerca volvulus / isolation & purification
  • Onchocerca volvulus / physiology
  • Onchocerciasis / drug therapy
  • Onchocerciasis / epidemiology
  • Onchocerciasis / prevention & control*
  • Onchocerciasis / transmission
  • Simuliidae / parasitology*
  • Simuliidae / physiology

Substances

  • Anthelmintics
  • Ivermectin

Grant support

This study was supported by the Onchocerciasis Elimination Program for the Americas (The Carter Center), the Bill and Melinda Gates Foundation, and Lions Clubs International Foundation. Merck & Co, through the Mectizan Donation Program, has donated all the ivermectin through the years. The Ministry of Health Mexico (Centro Nacional de Programas Preventivos y Control de Enfermedades) and the Health Services of the States of Oaxaca and Chiapas also supported this study as part of their tenure. MARP holds a sabbatical scholarship from CONACYT-Mexico (Reference No. 246116), which allowed the completion of the present article. He is also supported by Comisión de Operación y Fomento de Actividades Académicas del IPN. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.