Modelling the effects of immigration on the re-introduction of onchocerciasis
File(s)
Published version
Author(s)
Stapley, Jacob N
Basanez, Maria-Gloria
Ramani, Aditya
Walker, Martin
Hamley, Jonathan ID
Type
Journal Article
Abstract
Background Onchocerciasis is a filarial neglected tropical disease targeted by the World Health Organization for elimination (interruption) of transmission (EOT), principally by mass drug administration (MDA) with ivermectin. Variable effectiveness and success of MDA,
among other factors, has led to a markedly heterogeneous contemporary spatial landscape of
endemicity and transmission, with some foci having achieved or nearing EOT, while in others, transmission persists despite decades of MDA or has only recently been identified. Communities reaching EOT or free from infection are thus vulnerable to re-introduction of
infection imported by immigrants from areas with ongoing transmission.
Methods We use the stochastic, individual-based EPIONCHO-IBM transmission model to quantify the risk of transmission persistence resulting from importation events and characterise the dynamics of ensuing onchocerciasis outbreaks in terms of microfilarial
prevalence (in all ages) and anti-Ov16 seroprevalence (in children aged 5-9 years) in infection-free communities with local populations of blackfly vectors.
Results We show how the vulnerability of infection-free communities depends on their population size, the local annual biting rate (ABR, number bites/person/year) and on the magnitude of importation events, defined by the number of immigrants arriving in the community and their worm burdens. We show that small communities with modest ABRs are particularly vulnerable to transmission persistence following importation, with risk exacerbated by the magnitude of infection importation. We illustrate that onchocerciasis outbreak dynamics can be protracted, with seroprevalence in children often taking substantially longer than the currently recommended 3-5 years of post-treatment surveillance
(PTS) to exceed 5%.
Conclusions Our findings highlight the vulnerability of infection-free communities to introduction/re-introduction of infection and suggest that proposed PTS durations may need to be extended and complemented with additional surveillance activities and migration
studies to detect and respond robustly to nascent outbreaks and sustain elimination.
among other factors, has led to a markedly heterogeneous contemporary spatial landscape of
endemicity and transmission, with some foci having achieved or nearing EOT, while in others, transmission persists despite decades of MDA or has only recently been identified. Communities reaching EOT or free from infection are thus vulnerable to re-introduction of
infection imported by immigrants from areas with ongoing transmission.
Methods We use the stochastic, individual-based EPIONCHO-IBM transmission model to quantify the risk of transmission persistence resulting from importation events and characterise the dynamics of ensuing onchocerciasis outbreaks in terms of microfilarial
prevalence (in all ages) and anti-Ov16 seroprevalence (in children aged 5-9 years) in infection-free communities with local populations of blackfly vectors.
Results We show how the vulnerability of infection-free communities depends on their population size, the local annual biting rate (ABR, number bites/person/year) and on the magnitude of importation events, defined by the number of immigrants arriving in the community and their worm burdens. We show that small communities with modest ABRs are particularly vulnerable to transmission persistence following importation, with risk exacerbated by the magnitude of infection importation. We illustrate that onchocerciasis outbreak dynamics can be protracted, with seroprevalence in children often taking substantially longer than the currently recommended 3-5 years of post-treatment surveillance
(PTS) to exceed 5%.
Conclusions Our findings highlight the vulnerability of infection-free communities to introduction/re-introduction of infection and suggest that proposed PTS durations may need to be extended and complemented with additional surveillance activities and migration
studies to detect and respond robustly to nascent outbreaks and sustain elimination.
Date Issued
2026-01-28
Date Acceptance
2025-12-12
Citation
Parasites and Vectors, 2026, 19 (1)
ISSN
1756-3305
Publisher
BMC
Journal / Book Title
Parasites and Vectors
Volume
19
Issue
1
Copyright Statement
© The Author(s) 2026. Open Access This article is licensed under a Creative Commons Attribution 4.0 International License, which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons licence, and indicate if changes were made. The images or other third party material in this article are included in the article’s Creative Commons licence, unless indicated otherwise in a credit line to the material. If material is not included in the article’s Creative Commons licence and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder. To view a copy of this licence, visit http://creativecommons.org/licenses/ by/4.0/. The Creative Commons Public Domain Dedication waiver (http://creativecommons.org/publicdomain/zero/1.0/) applies to the data made available in this article, unless otherwise stated in a credit line to the data.
License URL
Identifier
10.1186/s13071-025-07213-z
Subjects
Onchocerciasis
Ivermectin
Immigration
Infection importation
Post-treatment surveillance
Postelimination surveillance
Microfilarial prevalence
Anti-Ov16 seroprevalence
Stochastic modelling
Publication Status
Published
Article Number
53
Date Publish Online
2026-01-14