| Summary: | Using reverse genetics, we analyzed a chikungunya virus (CHIKV) isolate of the Indian Ocean lineage lacking direct repeat (DR) elements in the 3′ untranslated region, namely DR1a and DR2a. While this deletion mutant CHIKV-∆DR exhibited growth characteristics comparable to the wild-type virus in Baby Hamster Kidney cells, replication of the mutant was reduced in <i>Aedes albopictus</i> C6/36 and <i>Ae. aegypti</i> Aag2 cells. Using oral and intrathoracic infection of mosquitoes, viral infectivity, dissemination, and transmission of CHIKV-∆DR could be shown for the well-known CHIKV vectors <i>Ae. aegypti</i> and <i>Ae. albopictus</i>. Oral infection of <i>Ae. vexans</i> and <i>Culex pipiens</i> mosquitoes with mutant or wild-type CHIKV showed very limited infectivity. Dissemination, transmission, and transmission efficiencies as determined via viral RNA in the saliva were slightly higher in <i>Ae. vexans</i> for the wild-type virus than for CHIKV-∆DR. However, both <i>Ae. vexans</i> and <i>Cx. pipiens</i> allowed efficient viral replication after intrathoracic injection confirming that the midgut barrier is an important determinant for the compromised infectivity after oral infection. Transmission efficiencies were neither significantly different between <i>Ae. vexans</i> and <i>Cx. pipiens</i> nor between wild-type and CHIKV-∆DR. With a combined transmission efficiency of 6%, both <i>Ae. vexans</i> and <i>Cx. pipiens</i> might serve as potential vectors in temperate regions.
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