Spatiotemporal transmission dynamics of co-circulating dengue, Zika, and chikungunya viruses in Fortaleza, Brazil: 2011-2017

The mosquito-borne viruses dengue (DENV), Zika (ZIKV), and chikungunya (CHIKV), now co-endemic in the Americas, pose growing threats to health worldwide. However, it remains unclear whether there exist interactions between these viruses that could shape their epidemiology. This study advances knowledge by assessing the transmission dynamics of co-circulating DENV, ZIKV, and CHIKV in the city of Fortaleza, Brazil. Spatiotemporal transmission dynamics of DENV, ZIKV, and CHIKV were analyzed using georeferenced data on over 210,000 reported cases from 2011 to 2017 in Fortaleza, Brazil. Local spatial clustering tests and space-time scan statistics were used to compare transmission dynamics across all years. The transmission of co-circulating viruses in 2016 and 2017 was evaluated at fine spatial and temporal scales using a measure of spatiotemporal dependence, the tau-statistic. Results revealed differences in the diffusion of CHIKV compared to previous DENV epidemics and spatially distinct transmission of DENV/ZIKV and CHIKV during the period of their co-circulation. Significant spatial clustering of viruses of the same type was observed within 14-day time intervals at distances of up to 6.8 km (p0.05). These results suggest that arbovirus risk is not uniformly distributed within cities during co-circulation. Findings may guide outbreak preparedness and response efforts by highlighting the clustered nature of transmission of co-circulating arboviruses at the neighborhood level. The potential for competitive interactions between the arboviruses should be further investigated. Author summary Most of the global population is at risk of infection with dengue, Zika, and chikungunya viruses, all transmitted by the Aedes mosquitoes. Although these viruses now circulate together in the Americas, it is not known how, if at all, they might interact inside co-infected vectors or hosts. Such interactions could serve as important determinants of transmission in the context of co-circulation. We used seven years of surveillance data from Fortaleza, the fifth largest city in Brazil, to investigate the potential effects of co-circulation on the transmission dynamics of the three Aedes-borne viruses. We found that, during years with co-circulation, different families of viruses (dengue/Zika and chikungunya) clustered in distinct areas of the city. This spatial clustering of viruses of the same type was maintained even within narrow time intervals. Transmission patterns in epidemic years with co-circulation deviated from patterns in previous epidemic years. Our findings suggest that co-circulation may alter the transmission dynamics of these mosquito-borne viruses. Further research is needed to confirm any competitive interactions between the viruses and to establish evidence-based public health recommendations for concurrent outbreaks.