Hypothesis: do invasive house geckos exacerbate dengue fever epidemics?
Dengue fever is a mosquito-borne disease that has undergone a marked rise in incidence since the 1950s, throughout the world's tropical regions. Here, we present a hypothesis that this rise in incidence may have been exacerbated by the invasion of house geckos, due to their role in the mosquito vector food web. Previous research has shown that in the absence of a top predator, house geckos reach high densities, directly affecting spider densities and indirectly resulting in higher Aedes-mosquito densities. Hence, we expect that in areas where house geckos are invasive and an effective top predator is lacking, Aedes densities will be higher, resulting in a higher dengue fever incidence rate. We perform a preliminary test of this hypothesis by looking for patterns in secondary country-level data to estimate the global range of invasive house gecko species over time. We related these estimated ranges to variation in the number of per capita dengue cases in 80 different countries. The incidence of dengue was significantly higher in countries where house geckos were introduced, when compared with countries where it was either native or absent. In addition, in countries where house geckos were introduced earlier and had time to become naturalized, dengue fever incidence rates were higher than for countries where house geckos were introduced more recently. These results suggest that house geckos could indeed have played a role in the rise of dengue in tropical countries. Here, we present a framework for the required experimental research to test the mechanism underlying these observations.