Elimination of African onchocerciasis: modeling the impact of increasing the frequency of ivermectin mass treatment

PLoS One. 2014 Dec 29;9(12):e115886. doi: 10.1371/journal.pone.0115886. eCollection 2014.

Abstract

The African Programme for Onchocerciasis Control (APOC) is currently shifting its focus from morbidity control to elimination of infection. To enhance the likelihood of elimination and speed up its achievement, programs may consider to increase the frequency of ivermectin mass treatment from annual to 6-monthly or even higher. In a computer simulation study, we examined the potential impact of increasing the mass treatment frequency for different settings. With the ONCHOSIM model, we simulated 92,610 scenarios pertaining to different assumptions about transmission conditions, history of mass treatment, the future mass treatment strategy, and ivermectin efficacy. Simulation results were used to determine the minimum remaining program duration and number of treatment rounds required to achieve 99% probability of elimination. Doubling the frequency of treatment from yearly to 6-monthly or 3-monthly was predicted to reduce remaining program duration by about 40% or 60%, respectively. These reductions come at a cost of additional treatment rounds, especially in case of 3-monthly mass treatment. Also, aforementioned reductions are highly dependent on maintained coverage, and could be completely nullified if coverage of mass treatment were to fall in the future. In low coverage settings, increasing treatment coverage is almost just as effective as increasing treatment frequency. We conclude that 6-monthly mass treatment may only be worth the effort in situations where annual treatment is expected to take a long time to achieve elimination in spite of good treatment coverage, e.g. because of unfavorable transmission conditions or because mass treatment started recently.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Africa / epidemiology
  • Animals
  • Computer Simulation
  • Disease Eradication*
  • Humans
  • Ivermectin / administration & dosage*
  • Ivermectin / supply & distribution
  • Ivermectin / therapeutic use*
  • Models, Biological*
  • Onchocerca volvulus
  • Onchocerciasis / drug therapy*
  • Onchocerciasis / epidemiology
  • Onchocerciasis / parasitology
  • Onchocerciasis / prevention & control*
  • Probability
  • Skin / parasitology
  • Time Factors
  • Treatment Outcome

Substances

  • Ivermectin

Grants and funding

The study was funded by the Mectizan Donation Program. ADH is the director of the Mectizan Donation Program. The funder provided support in the form of salary for author ADH, but did not have any additional role in the study design, data collection and analysis, decision to publish, or preparation of the manuscript. The specific role of this author is articulated in the “author contributions” section.