Aedes aegypti and dengue transmission in Cali, Colombia: Insecticide resistance, vector competence and population genetics

In Colombia, Aedes aegypti is the only known vector of dengue virus transmission, the agent responsible for dengue and dengue hemorrhagic fever. This mosquito is highly adapted to urban areas. Currently, mosquito control and avoidance are the only prophylactic measure available for these diseases.; In Cali, Colombia, the continued intense use of insecticides by mosquito control programs and the population in general has resulted in the emergence of insecticide resistance. In preliminary studies on Ae. aegypti populations from three localities in Cali during 1996–1999, variation was found, in time and place, and in the types of biochemical mechanisms (esterases and mixed function oxidases) responsible for insecticide resistance. These differences could be a product of distinct genetic populations. Insecticide pressure could induce the selection of insecticide resistance and, depending on the amount of gene flow among populations, could result in genetic differences among populations. To examine if Ae. aegypti in the city of Cali is a population with genetic distinct local populations that can generate differences in traits relevant to dengue transmission, biochemical mechanisms associated with insecticide resistance, vector competence for the dengue-2 virus, and population genetics by RAPD-PCR molecular markers were evaluated in Ae. aegypti populations from 5 localities separated by 4 to 8 km. The results from all the characteristics evaluated in the study demonstrated the presence of genetically differentiated populations in the city. Differential ongoing pressure from insecticides in Cali could be a major selective force that changes the genetic structure of mosquito populations. These results demonstrate that populations of Ae. aegypti in an urban is in continuous change in response to localized selective pressures which differ in time and place. The success of local vector control and severity of dengue transmission can be affected by these population level changes.