Heterogeneity in network structure switches the dominant transmission mode of infectious diseases

Several recent emerging diseases have exhibited both sexual and non-sexual transmission modes (Ebola, Zika and mpox). In the recent mpox outbreaks, transmission through sexual contacts appears to be the dominant mode of transmission. Motivated by this, we use an SIR-like model, to argue that an initially dominant sexual transmission mode can be overtaken by casual transmission at later stages, even if the basic casual reproduction number is less than one. Our results highlight the risk of intervention designs which are informed only by the early dynamics of the disease. Significance Statement The purpose of this article is to explore the risk from secondary transmission routes of diseases which spread through sexual contact. This is important because infectious diseases such as Ebola, Zika and mpox spread through both sexual transmission and other modes of transmission. Our results suggest that a secondary transmission route which is not dominant in the initial stages, can significantly alter the course of the epidemic and lead to more infections than expected in the later stages of the epidemic.