Laboratory vector competence of Culex (Melanoconion) cedecei for sympatric and allopatric Venezuelan equine encephalomyelitis viruses

Laboratory vector competence of Culex (Melanoconion) cedecei was examined for Venezuelan equine encephalomyelitis (VEE) viruses. Colonized adult female mosquitoes originating from a southern Florida population were given bloodmeals from viremic hamsters circulating various titers of 3 hemagglutination inhibition (HI) subtypes of VEE viruses. Following extrinsic incubation of about 3 weeks, mosquitoes were allowed to refeed on uninfected hamsters for transmission trials. Cx. cedecei was highly efficient in becoming infected with and transmitting its sympatric, HI subtype II 'Everglades' virus. With bloodmeal titers of 10^0.9 chick embryo cell culture (CEC) plaque forming units (PFU), the infection rate was 9% and transmission occurred following extrinsic incubation. Infection rates were ≥80% with oral doses of ≥10^1.8, and all infected mosquitoes were capable of transmission following incubation. Cx. cedecei was also highly sensitive to infection with allopatric HI subtype IE Middle American VEE virus isolates. Infection rates were ≥50% with bloodmeal titers undetectable by CEC assay. Rates were 100% with oral doses of ≥10^0.8 CECPFU. Transmission rates were 100% in all experiments. Similar results were obtained with HI subtype IAB 'epizootic' VEE virus isolates from the 1969 Middle American outbreak. Infection rates were 100% with oral doses of ≥10^1.2, and transmission rates were 100% after extrinsic incubation. Comparisons with laboratory vector competence of the Middle American enzootic VEE virus vector, Culex (Melanoconion) taeniopus, are discussed.