Dengue Vector Dynamics in Pakistan

During the last few year dengue has become an emerging vector borne disease in Pakistan. Aedes aegypti once considered eradicated from almost whole of Pakistan was again collected from 13 different cities. This mosquito has not only started reinvading its previously occupied areas (Karachi, Peshawar and Lahore) but is also spreading to new areas where it was not present before (Attock, Haripur, Hasanabdal, Taxilla, Rawalpindi, Gujranwala, Sheikhupura, Faisalabad, Multan and Hyderabad). This mosquito is breeding in almost all types of artificial containers especially in tyres. Though this mosquito is mostly using outdoors containers for ovipositon but was also found breeding indoors in household. Eleven microsatellite markers were used to determine the genetic population structure of Aedes aegypti in Pakistan using mosquitoes collected from 13 different cities. There appears to be a single population of this mosquito in Pakistan with a pattern of isolation by distance rather than distinct sub-populations. The large scale of isolation by distance suggests long range passive dispersal which may be facilitated by the tyre trade in Pakistan. A decrease in genetic diversity from north to south suggests a recent spread of this mosquito from Karachi. A strong negative correlation between genetic distance and quality of road connections between cities suggests human-aided passive dispersal of Ae. aegypti in Pakistan. Dengue detection in mosquitoes collected from different areas of Pakistan with special reference to tyres shows that vertical transmission is not playing any significant role in the maintenance of dengue virus in mosquito of population. Absence of virus in larvae collected from tyres suggest that though tyres are playing important role in the spread of vector mosquito in Pakistan but its not playing any role in the spread of dengue virus in the study area. The long-range dispersal of Aedes aegypti in Pakistan could facilitate the strategy of introducing transgenic Aedes aegypti or an intracellular bacterium, like the endosymbiotic Wolbachia, for controlling the population of this dengue vector in Pakistan.