Models of Trachoma Transmission and Their Policy Implications: From Control to Elimination

Abstract

Despite great progress in eliminating trachoma from the majority of worldwide districts, trachoma control seems to have stalled in some endemic districts. Can mathematical models help suggest the way forward? We review specific achievements of models in trachoma control in the past. Models showed that, even with incomplete coverage, mass drug administration could eliminate disease through a spillover effect, somewhat analogous to how incomplete vaccine campaigns can eliminate disease through herd protection. Models also suggest that elimination can always be achieved if enough people are treated often enough with an effective enough drug. Other models supported the idea that targeting ages at highest risk or continued improvements in hygiene and sanitation can contribute meaningfully to trachoma control. Models of intensive targeting of a core group may point the way to final eradication even in areas with substantial transmission and within-community heterogeneity.

Macrolide and Nonmacrolide Resistance with Mass Azithromycin Distribution

“…However, mass azithromycin distribution continues to be effective, despite the distribution of more than 860 million doses of azithromycin worldwide for the elimination of trachoma alone 26 , 27 . It remains the WHO’s recommendation for trachoma control 28 , 29 . In addition, the prevalence of antibiotic resistance has been shown to predictably decline when mass drug distributions are discontinued, at least for certain antibiotics such as azithromycin 30 , 31 .…”

Milestones in the fight to eliminate trachoma

“…The greatest burden of disease, 85% of all active trachoma cases, now resides in Africa where most of the intervention focus is directed. Mathematical models suggest that elimination, at least of active trachoma, in the next decade may be feasible . The milestones outlined above have created and supported a solid foundation for trachoma elimination programmes, and donors have recognised the value and pledged continued support into the future to ensure that this preventable cause of blindness is no longer a threat.…”

Toward the Elimination of Disease: the 2019 Weisenfeld Award Lecture

“…The current models of elimination suggest that the next decade may be a realistic target, providing conflict areas can be mapped and successful programs mounted. 31 Trachoma is but an example of how an elimination roadmap can work. Whatever the disease, however sophisticated the intervention, the five steps provide a simple set of milestones that can guide the process toward elimination: what is the pathogenesis, how can we intervene, who is the target for the intervention and where are they, and when can we declare victory.…”