The pyrethroid resistance status and mechanisms in Aedes aegypti from the Guerrero state, Mexico

Dengue is one of the most important vector-borne diseases worldwide and is a public health problem in Mexico. Most programs in dengue endemic countries rely on insecticides for Aedes control. In Mexico, pyrethroid insecticides (mainly permethrin and deltamethrin) have been extensively used over a decade as adulticides and represented a strong selection for insecticide resistance for dengue vectors in several parts of the country. We studied the type, frequency and distribution of insecticide resistance mechanisms in Aedes aegypti from six municipalities in the state of Guerrero selected on the basis of historically intense chemical control and a high risk for dengue transmission. Ae. aegypti eggs were collected from October 2009 to January 2010 using ovitraps. F1 adults, emerged from these collections, were exposed to permethrin, deltamethrin and DDT in WHO diagnostic tests and showed high resistance levels to both pyrethroids and DDT. This was consistent with the presence of increased metabolic enzyme activities and target site insensitivity due to kdr mutations. Biochemical assays showed elevated esterase and glutathione S-transferase activities in the six municipalities. The V1016I kdr mutation on the IIS6 domain of the sodium channel gene was present in an overall frequency of 0.80. A second mutation, F1534C on the IIIS6 domain of the same gene was also detected, being the first report of this mutation in Guerrero. The multiple resistance mechanisms present in Ae. aegypti from Guerrero state represent a warning for the efficacy of the pyrethroid usage and consequently for the success of the dengue control program