Aedes aegypti
Background about Aedes aegypti and Iquitos, Peru
Aedes aegypti is the major mosquito species that transmits Dengue virus, Zika virus, Chikungunya virus, and Yellow Fever to humans. I study the population of Aedes aegypti in Iquitos, Peru to better understand how to control disease epidemics. My lab collaborates with researchers UC Davis and the Navy Medical Research Unit - 6 in Iquitos, Peru who have been studying and collecting the species in this city for over 2 decades. I am using this collection to determine the dynamics of insecticide resistance evolution and address other population genomics questions within the city. These data will be used to better model mosquito population dynamics in order to predict the effectiveness of new and emerging control techniques.
Evolution of Insecticide Resistance
Pyrethroids are a class of neurotoxic insecticides that are commonly used to control mosquito populations because they are relatively safe to use around humans. Pyrethroids work by targeting the voltage-gated sodium channel gene, which controls part of the nervous system. When a susceptible mosquito is exposed to the insecticide, the sodium channel opens and the nerves are constantly firing. This results in the insects becoming paralyzed and dying if exposed to a high enough dose. Several genetic mutations have occurred and spread through many Aedes aegypti populations that prevent the pyrethroids from causing this response. Mosquitoes with one or more of these mutations are said to be "resistant." I have genotyped mosquitoes collected over the past two decades from Iquitos, Peru to determine when specific mutations arose in the population and how quickly they spread.
The two mutations that I have examined are known as V1016I and F1534C. These single nucleotide polymorphisms (SNPs, pronounced "snips") are not the only mutations found in this gene, but they have been shown to be important in other Aedes aegypti populations in Mexico and Brazil. I have found that resistance spread rapidly through the city once the mutations appeared. And, importantly, that these mutations appear to be partially dominant. This is important because the degree of dominance of a muation affects the rate at which it can spread in a population. The stronger the dominance, the faster the mutation will spread.
kdr haplotype frequencies from 2000 to 2017. Shaded areas represent periods when pyrethroids were used or not. The specific type of pyrethroid is abbreviated in the shaded area (i.e., Delta = deltamethrin, Cyper = cypermethrin, and Alpha = alpha-cypermethrin). Multiple* represents a period from 2012 to 2013 where multiple chemistries were used, including cypermethrin, alpha-cypermethrin, lambda-cyhalothrin, and alpha-cypermethrin+pyriproxyfen. The number of individuals genotyped per year are shown below y = 0.0. Error bars = 95% CI.
View the published paper for this work in Evolutionary Applications.
Digging Deeper into Pyrethroid Resistance Evolution
Coming soon...