Zika Endemicity Lowers the HIV Invasion Threshold: A Mathematical Model of Zika‐HIV Coinfection

ABSTRACT The coexistence of Zika virus (ZIKV) and HIV across tropical areas presents important research opportunities to examine how vector‐borne pathogens affect trends of sexually transmitted diseases. We create a detailed mathematical model that combines vector‐borne transmission with sexual transmission, antiretroviral treatment, coinfection disease development, human movement across multiple population systems, and seasonal changes in mosquito populations, which are forced by climate. The research presents a new concept that defines an effective coinfection invasion reproduction number that describes how HIV establishes itself in populations where the Zika virus circulates. Analytical results demonstrate that endemic Zika transmission decreases the HIV invasion threshold, which allows HIV to survive even when the classical HIV reproduction number falls below one. The analysis of the center manifold and bifurcation demonstrates that the threshold reduction happens through forward transcritical bifurcations. The coinfection persistence patterns reveal three main factors: mosquito biting intensity, HIV transmission rate, and ART‐related parameters, while spatial connectivity and climate variability increase the epidemic burden. The study shows that co‐endemic areas need climate‐aware treatments based on human mobility patterns to create successful intervention strategies.