Limited Vector Competence of Culex quinquefasciatus and Aedes aegypti for Oropouche Virus in Florida

Oropouche virus (OROV) is a medically important orthobunyavirus that causes Oropouche fever, a febrile illness that can occasionally progress to neurological complications. Since its discovery in Trinidad in 1955, OROV has caused recurrent outbreaks across South America, with more than 500,000 reported cases. In 2024, over 100 travel-associated OROV infections were documented in the continental United States, including 103 cases in Florida, raising concerns about the potential for local transmission if competent vectors feed on viremic individuals. OROV is primarily transmitted by the biting midge Culicoides paraensis, and the three-toed sloth (Bradypus spp.) has been identified as a natural vertebrate host. Recent laboratory studies have shown that emerging OROV strains replicate more efficiently in human cell lines than ancestral strains, suggesting that these variants may also be transmissible by mosquito species that frequently feed on humans. To investigate this possibility, we assessed the vector competence of Florida populations of Culex quinquefasciatus and Aedes aegypti for both a prototype (TRVL9760, 1955) and an emerging (240023, 2024) strain of OROV. Experiments were conducted under laboratory conditions using two virus incubation periods in cell culture (5 or 7 days) and three extrinsic incubation periods (7, 14, or 21 days), which are key factors known to influence arbovirus transmission dynamics under varying ecological and virological conditions. A total of 1,877 mosquitoes were processed for OROV detection. Infection rates varied by mosquito species (or strain), viral genotype, and incubation period. Both species exhibited moderate susceptibility to infection, with viral RNA detected in mosquito bodies at rates ranging from 24.2% in Cx. quinquefasciatus to 43.2% in Ae. aegypti (Lower Keys population). Disseminated infections were also observed, with viral RNA detected in legs and wings at rates from 23.0% in Cx. quinquefasciatus to 57.5% in Ae. aegypti. However, transmission via saliva was infrequent (<2.5%), likely due to midgut and salivary gland barriers restricting viral escape. These findings suggest that although Cx. quinquefasciatus and Ae. aegypti can support partial replication of OROV, they are unlikely to facilitate sustained local transmission in Florida. This study highlights the importance of continued arbovirus surveillance and vector competence assessments in regions at risk of OROV introduction.

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