Combining data analysis and transmission modelling to support the control and elimination of onchocerciasis in africa
File(s)
Author(s)
Stapley, Jacob N
Type
Thesis
Abstract
Human onchocerciasis (river blindness) is a neglected tropical disease caused by Onchocerca volvulus and is transmitted by Simulium blackflies. The disease was once endemic across Latin America, Yemen and sub-Saharan Africa (SSA), the latter harbouring 99% of remaining disease burden. Onchocerciasis primarily causes disability, however, in high transmission settings, O. volvulus infection has also been linked to onchocerciasis-associated epilepsy (OAE), a known cause of premature mortality. Control efforts began in 1974 with anti-vectorial measures in West Africa. The introduction of mass drug administration (MDA) with ivermectin in 1987 has significantly reduced prevalence and morbidity, leading to elimination in some foci. The 2012 WHO NTD Roadmap set a target for elimination of transmission (EOT) in selected African countries by 2020. However, modelling studies in 2019 indicated that annual MDA alone may be insufficient, prompting calls for complementary interventions. The 2021-2030 WHO Roadmap set a goal of verifying EOT in 12 countries by 2030, recognising challenges in achieving EOT everywhere under current strategies. This thesis employs EPIONCHO-IBM, an individual-based transmission model, to examine hypoendemic transmission dynamics and the risks of re-introduction. Key findings indicate that onchocerciasis transmission may persist at low annual biting rates (ABR) without importation, with threshold biting rates as low as 70 bites per person per year. This suggests that low-prevalence settings should be included in MDA programmes. Modelled anti-Ov16 seroprevalence thresholds align with WHO guidelines, reinforcing the need for a conservative approach when initiating MDA. Modelling also highlights that immigration of infected individuals poses a significant risk to elimination efforts. Additionally, by integrating OAE into EPIONCHO-IBM, the thesis quantifies the impact of ivermectin MDA on OAE prevalence and underscores the need for alternative treatments, such as moxidectin, for young children. These findings contribute to refining onchocerciasis transmission models and advancing elimination strategies across SSA.
Version
Open Access
Date Issued
2025-01-05
Date Awarded
01/05/2025
License URL
Advisor
Basanez, Maria-Gloria
Walker, Martin
Hamley, Jonathan
Publisher Department
Department of Infectious Disease
Publisher Institution
Imperial College London
Qualification Level
Doctoral
Qualification Name
Doctor of Philosophy (PhD)