Enhanced infection and transmission of the 2022-2024 Oropouche virus strain in the North American biting midge Culicoides sonorensis

Authors: Scroggs, Stacey; Gutierrez, Jessica; Reister-Hendricks, Lindsey; GUNTER, KRISTA - Indiana University School Of Medicine; TILSTON, NATASHA - Indiana University School Of Medicine; McGregor, Bethany

Submitted to: Scientific Reports
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/9/2025
Publication Date: 7/28/2025
Citation: Scroggs, S.L., Gutierrez, J., Reister-Hendricks, L.M., Gunter, K.B., Tilston, N.L., Mcgregor, B.L. 2025. Enhanced infection and transmission of the 2022-2024 Oropouche virus strain in the North American biting midge Culicoides sonorensis. Scientific Reports. 15:27368. https://doi.org/10.1038/s41598-025-11337-8.
DOI: https://doi.org/10.1038/s41598-025-11337-8

Interpretive Summary: The recent 2022–2024 outbreak of Oropouche virus (OROV), a midge-borne disease that causes a febrile illness in humans, has presented an unusual rise in cases, spread to new regions, and presented with novel symptoms not previously associated with the virus. With this unprecedented spread, OROV could emerge into the United States and threaten public health. The current study compared a newly circulating outbreak strain (OROV240023) to a historical strain (OROVBeAn19991) in Culicoides sonorensis, a species of biting midge widely distributed across North America. C. sonorensis midges infected with the outbreak strain had significantly higher infection, viral dissemination to the head, and ability to transmit the virus compared to those infected with the older strain. Interestingly, although both strains produced similar levels of virus, the outbreak strain was detected in the midge faster—becoming transmissible in under 5 days, as opposed to the 7–14 days required for the older strain. This shortened extrinsic incubation time means the virus can spread more quickly. These findings suggest that genetic changes in the outbreak strain may be contributing to its heightened transmission potential, raising alarms about the possibility of local spread and establishment if the virus emerges into the United States.

Technical Abstract: Oropouche virus (OROV) is a vector-borne zoonotic virus that causes febrile illness in humans. Biting midges of the Culicoides genus are the primary vector during human outbreaks. The 2022-2024 OROV outbreak has seen an increase in incidence, geographic expansion, and the emergence of previously undocumented symptoms. To better understand the basis of increased disease incidence, infection of the outbreak virus (OROV240023) was compared to a historical virus strain (rOROVBeAn19991) in Culicoides sonorensis, a midge species that has demonstrated historical competence. Higher levels of infection, dissemination, and transmission potential were observed in C. sonorensis infected with the outbreak strain compared to the historical strain, although infectious titers did not differ between the two viruses. OROV240023 was also detected in saliva at earlier time points than rOROVBeAn19991, indicating a shorter extrinsic incubation period of < 5 days compared to 7-14 days for rOROVBeAn19991. Taken together, our results demonstrate increased transmission potential of the outbreak strain in C. sonorensis midges, raising concern about the risk of spread within the United States following potential introduction. However, further studies are needed to evaluate the current strain in Culicoides species circulating within its outbreak range, including Culicoides paraensis, the confirmed South American vector of OROV.