Why can dengue and Zika become more difficult to control when they circulate in the same population?
This study develops a mathematical model for examining the combined transmission of dengue and Zika in regions where both diseases are spread by Aedes aegypti mosquitoes.
The model contains 16 compartments covering susceptible, exposed, infected, treated, recovered, vaccinated, and co-infected humans, together with susceptible and infected mosquito populations.
It incorporates several important biological features, including antibody-dependent enhancement, partial cross-immunity, imperfect dengue vaccination, increased mortality during co-infection, mosquito-borne transmission, and direct human-to-human transmission of Zika.
The researchers derived separate reproduction numbers for dengue and Zika and showed that the overall reproduction number for the combined system is at least as large as the reproduction number of either disease alone. This means that single-disease models may underestimate epidemic risk when both viruses circulate together.
The analysis also revealed backward bifurcation in both disease submodels. This means that reducing the reproduction number below one may not be sufficient to eliminate transmission because stable endemic infection can continue under certain conditions.
The model was calibrated using 36 weeks of reported dengue and Zika cases from Espรญrito Santo State, Brazil, covering January to September 2021. The fitted model reproduced the general epidemic patterns, with Pearson correlation values of 0.594 for dengue and 0.739 for Zika.
Sensitivity analysis identified mosquito biting rate and mosquito mortality as the most influential factors controlling transmission. Higher biting rates sharply increased dengue, Zika, and co-infection cases, while increasing mosquito mortality substantially reduced disease spread.
The simulations showed that doubling mosquito mortality could suppress peak dengue incidence by approximately 120-fold. Increased treatment-seeking also reduced dengue, Zika, and co-infection burdens.
Antibody-dependent enhancement further amplified co-infection by increasing susceptibility to one virus during infection with the other. This effect produced a nonlinear rise in the number of co-infected individuals as mosquito exposure increased.
Vaccination reduced dengue transmission, but the findings showed that vaccine coverage and effectiveness must remain sufficiently high. Weak vaccination programmes may not overcome the persistence associated with backward bifurcation.
The study concludes that sustained vector control should form the foundation of dengueโZika prevention. Measures that reduce mosquito survival and humanโmosquito contact should be combined with timely treatment, improved healthcare access, surveillance, and high-coverage dengue vaccination.
The findings provide policymakers with a data-informed framework for designing integrated interventions in regions facing the simultaneous circulation of dengue and Zika.
๐ Read the full article here:
https://doi.org/10.46481/jnsps.2026.3405
Published in: Journal of the Nigerian Society of Physical Sciences