Oropouche virus: transmission, epidemiology, genetic diversity, and public health implications.

To the Editor: Oropouche virus (OROV), a member of the Bunyaviridae family, Orthobunyavirus genus, Simbu serogroup, is transmitted to humans in urban areas by the biting midge Culicoides paraensis and causes epidemic acute febrile disease (1). Since its first isolation in Trinidad in 1955 (2), OROV has been associated with large outbreaks in South and Central America; half a million cases have been described during the past 45 years (1). The tripartite genome of OROV comprises single-strand, negative-sense large (L), medium (M), and small (S) RNAs that encode RNA polymerase, glycoproteins, and nucleocapsid, respectively. Studies have indicated the existence of 3 genotypes of OROV circulating in Brazil: genotypes I and II in the Amazon Basin and genotype III in the Southeast Region (3–5). OROV causes explosive urban epidemics. Serologic evidence of exposure to OROV in populations not affected by known outbreaks suggests that the virus circulates endemically (1). However, no sporadic infections have been reported. Here we report a sporadic OROV infection detected by clinical and laboratory surveillance of acute febrile illnesses in Acre, a state in the western Amazon region of Brazil. From March 2004 through October 2006, we prospectively investigated 69 febrile episodes in persons 6–60 years of age (mean, 28.1 years) living in the town of Acrelândia (10°13′W, 67°00′S) and surrounding rural areas (25.7% and 74.3% of the sample, respectively). Serum samples for reverse transcription–PCR (RT-PCR) were stored in liquid nitrogen in the field and shipped on dry ice to the laboratory in Sao Jose do Rio Preto, 3,500 km southeast of Acre. Because malaria and several arboviruses are locally endemic (6), all patients were screened for malarial parasites by thick-smear microscopy and for flaviviruses and alphaviruses by multiplex-nested RT-PCR (7). The samples negative for both malaria and other arboviruses were further tested for OROV with primers targeting the S segment of the OROV genome in a seminested RT-PCR strategy (R.V.M. Bronzoni et al., unpub. data; primers and protocol available from the authors by request). The sample also was isolated in Vero cells, and the RT-PCR described by Moreli et al. (8) was used for confirmation. We sequenced amplicons by using the same primers used for RT-heminested amplification and by using BigDye Terminators version 3.1 (ABI, Foster City, CA, USA) in ABI377 automated sequencer. Sequences were edited by DSGene 2.0 (Accelrys, San Diego, CA, USA) and deposited in GenBank (accession no. {type:entrez-nucleotide,attrs:{text:EU561644,term_id:189212452,term_text:EU561644}}EU561644). One (1.4%) of 69 samples tested for OROV by heminested PCR was positive. This sample (BR/2004/ACRE27) was collected from a male patient from a rural area in April 2004. Precautions were followed to avoid contamination; positive and negative controls were used in all reactions; and the procedure was reproduced several times. The patient had ill-defined, mild flu-like symptoms; low-grade fever; and nasal discharge but reported no headache or other major symptoms. He recovered without complication. We built a phylogenetic tree on the basis of the 522 nucleotide sequences (27–200 aa) of nucleocapsid protein gene of OROV sample BR/2004/ACRE27 and other GenBank sequences from different OROV genotypes. We used sequences from Aino, Akabane, and Tinaroo viruses as the outgroup. A phylogenetic analysis was performed by the neighbor-joining method by using the Kimura 2-parameter nucleotide substitution model (9). The tree showed 3 main clades, corresponding to genotypes I, II, and III, and BR/2004/ACRE27 grouped within genotype I strains (Figure). Both genotypes I and II have been described in OROV outbreaks in Acre; genotype I, however, is found mostly in Para in the eastern part of the Brazilian Amazon region. Figure Phylogenetic tree of Oropouche virus strains; boldface shows the sample from the patient in this study. Phylogenetic tree was constructed from partial nucleocapsid gene sequence (522 nt, 27–200 aa) by neighbor-joining method implemented in MEGA ... A baseline serologic survey in rural Acrelândia during March and April 2004 detected antibodies to OROV in 6 (1.7%) of 357 persons 5–90 years of age who were examined by microplaque hemagglutination inhibition (10). Because none of these persons had been exposed to known OROV outbreaks in Acre or elsewhere, these findings further suggest the sporadic circulation of OROV in the area. We describe a sporadic infection of OROV infection in the Amazon region of Brazil in a mildly symptomatic patient. The nucleocapsid gene of the isolate has been sequenced, placing it in the genotype I group, the most commonly found in the Amazon Basin. These data suggest that OROV circulation may be sporadic and clinically silent and, when not associated with outbreaks, most likely neglected by local physicians.

The spatiotemporal ecology of Oropouche virus across Latin America: a multidisciplinary, laboratory-based, modelling study.

Epidemiology, transmission dynamics, treatment strategies, and future perspectives on Oropouche virus.

Oropouche virus (OROV) is an emerging arbovirus of growing public health concern, with increasing incidence and geographic spread. Since its discovery in 1955, OROV has caused multiple outbreaks in South and Central America, with a new introduction in Cuba since May 2024. Recent travel-related cases in Europe and the Americas underscore its potential for global dissemination. Assessing vector competence outside endemic regions is critical in the context of global travel and climate change. We evaluated the vector competence of three mosquito species commonly found in Europe—Culex (Cx.) pipiens, Aedes (Ae.) albopictus, and Anopheles (An.) atroparvus—using two OROV strains: the prototype TRVL9760 (1955, Trinidad and Tobago) and a recent isolate OROV-IRCCS-SCDC_1/2024 (2024, imported from Cuba to Italy). Mosquitoes were orally infected and examined at 7- and 14-days post-infection. We assessed infection (body), dissemination (peripheral tissues), and transmission potential (saliva) by measuring infectious virus particles using the gold standard focus-forming assays. Our findings show that Cx. pipiens and An. atroparvus were not susceptible to infection or did not allow transmission with OROV. In Ae. albopictus, low infection rates were observed: 6.7% of mosquitoes showed infection at day 7 with the prototype strain, and 3.1% at day 14 with OROV-IRCCS-SCDC_1/2024. All infected mosquitoes showed viral dissemination, but none had infectious virus in their saliva, indicating low risk for transmission. These results confirm limited vector competence of European mosquito species for OROV and emphasize the importance of continued entomological surveillance to inform future risk assessments.

BackgroundIn 2024, Italy reported its first five cases of Oropouche fever in travelers returning from Cuba and Brazil. The Oropouche virus (OROV), an emerging Orthobunyavirus of the Peribunyaviridae family, is a zoonotic arbovirus responsible for febrile illnesses in humans, often misdiagnosed owing to its clinical similarity to those caused by dengue and Zika virus infections. Originally endemic to the Amazon region and first detected in Trinidad and Tobago in 1955, OROV has since spread throughout South and Central America. Recent outbreaks in Brazil and Cuba have been linked to the newly identified genotype V. Although Culicoides paraensis midges are recognized as the primary vector in the urban transmission cycle, their presence in Cuba was documented only after the outbreak.This late detection, coupled with a possibly low population density of this species, has raised concerns that other, more abundant arthropod species may have played a role in transmitting OROV to humans on the island. While some mosquito species have been implicated as potential OROV secondary vectors, their role remains uncertain. This study evaluates the vector competence of Italian populations of Aedes albopictus and Culex pipiens for the newly circulating OROV strain, which was introduced into the country by infected travelers. MethodsExperimental infections were conducted under biosafety level 3 conditions, exposing adult female mosquitoes to an infectious blood meal containing OROV. Viral presence was assessed using a real-time RT-PCR in mosquito bodies, legs + wings, saliva, and the first gonotrophic progeny (F1). ResultsResults indicated that, while both species successfully ingested infectious virus particles, Cx. pipiens exhibited no signs of infection, dissemination, or transmission at any time point. In Ae. albopictus, viral RNA was detected in two body samples but not in saliva or disseminated tissues, confirming an absence of transmission capability. In addition, no evidence of transmission to F1 generation was detected in either species. These findings are consistent with previous research on American mosquito populations, indicating that barriers to OROV transmission likely occur at the midgut level.ConclusionsDespite the apparent lack of vector competence in Italian Ae. albopictus and Cx. pipiens, the ongoing geographic expansion of OROV highlights the need for continued surveillance, particularly as the 2025 vector activity season approaches in Europe. The increasing circulation of the virus, along with its potential for adaptive evolution, highlights the importance of further research into the virus–vector interactions that could enable OROV to establish itself in new ecological niches.Graphical abstract

Introduction: Orthobunyavirus oropoucheense, formerly Oropouche virus (OROV), is a re-emerging arbovirus, responsible for large-scale outbreaks across the Americas. Culicoides paraensis and Culex quinquefasciatus have been described as the main urban vectors, while Coquillettidia venezuelensis and Aedes serratus are proposed to maintain sylvatic circulation. The 2023-2025 outbreak, marked by the emergence of novel viral lineages and the introduction of OROV to Cuba, a previously nonendemic region, suggests potential shifts in vector ecology, the establishment of an urban cycle independent of wildlife reservoirs, and viral mutations with implications for vector competence. Methods: This study presents a systematic review of entomovirological field evidence for OROV molecular detection, and vector competence experiments published up to July 2025. Six articles on molecular surveillance and 11 on vector competence were selected from peer-reviewed journals and preprint repositories and analyzed using a minimum data and metadata standard for vector competence experiments. Results: OROV viral detection studies have only been conducted in Cuba, Brazil and Peru since 2013, with pool positivity rates ranging 0.4-56% in Culicoides insignis, Limatus durhamii, Aedes albopictus, Ae. aegypti, Psorophora cingulata and Haemagogus tropicalis, suggesting their potential role as urban and sylvatic vectors. Specifically, Ceratopogonids Cu. paraensis and Cu sonorensis consistently demonstrate high transmission capacity (~30%), while mosquitoes (including Aedes, Culex and Psorophora spp.) exhibit low infection rates (<20%), and limited OROV transmission, implying midgut-level barriers. Furthermore, transmission was recently demonstrated in European lineages of Ae. albopictus (~12.5%), in specimens kept at 27 °C, 21 days post-infection, highlighting the need for temperature-based risk assessment, particularly in the Mediterranean basin. Conclusions: These findings suggest that OROV remains a neglected virus, despite the scale of its epidemiological impact. Expanded genomic surveillance and vector competence research are needed to better understand OROV ecology at the sylvatic-urban interface, and to assess the risk of spread and establishment in non-endemic regions, especially beyond the Americas.

Oropouche virus (OROV) is a neglected and emerging arbovirus that infects humans and animals in South and Central America. OROV is primarily transmitted to humans through the bites of infected midges and possibly some mosquitoes. It is the causative agent of Oropouche fever, which has high morbidity but low mortality rates in humans. The disease manifests in humans as high fever, headache, myalgia, arthralgia, photophobia, and, in some cases, meningitis and encephalitis. Additionally, a recent report suggests that OROV may cause fetal death, miscarriage, and microcephaly in newborns when women are infected during pregnancy, similar to the issues caused by the Zika virus (ZIKV), another mosquito-borne disease in the same regions. OROV was first reported in the mid-20th century in the Amazon basin. Since then, over 30 epidemics and more than 500,000 infection cases have been reported. The actual case numbers may be much higher due to frequent misdiagnosis, as OROV infection presents similar clinical symptoms to other co-circulating viruses, such as dengue virus (DENV), chikungunya virus (CHIKV), ZIKV, and West Nile virus (WNV). Due to climate change, increased travel, and urbanization, OROV infections have occurred at an increasing pace and have spread to new regions, with the potential to reach North America. According to the World Health Organization (WHO), over 10,000 cases were reported in 2024, including in areas where it was not previously detected. There is an urgent need to develop vaccines, antivirals, and specific diagnostic tools for OROV diseases. However, little is known about this surging virus, and no specific treatments or vaccines are available. In this article, we review the most recent progress in understanding virology, transmission, pathogenesis, diagnosis, host-vector dynamics, and antiviral vaccine development for OROV, and provide implications for future research directions.

The Oropouche virus (OROV) is emerging as a major public health threat worldwide, yet for the Americas, it raises complex challenges that intersect with other existing arboviral threats such as Zika (ZIKV), dengue (DENV) and Chikungunya (CHIKV) viruses. Originating from Trinidad and Tobago in 1955, it has spread across the Amazonian Basin and more recently into the Caribbean (Cuba and Haiti) and Europe, highlighting the importance of air travel in its dissemination. OROV and the less studied Melao virus (MELV), pose significant laboratory diagnostic challenges particularly in regions co-endemic with other arboviral diseases, such as dengue and Zika fever. The effects of climate change, particularly in the Caribbean, may exacerbate the transmission of these viruses by exposing human exposure risk to vectors. Public health systems in the Americas are under strain due to complex clinical management of these infections necessitating enhanced surveillance, clinical vigilance, diagnostics and vector control. Vulnerable populations, including pregnant women, elderly, and young children, are at a heightened risk, which raises concerns about the impact on medical tourism in the region. To mitigate the spread and impact of OROV and MELV, recommendations include increased clinical surveillance, improved laboratory diagnostics, public health communication, and strengthened vector controls. Robust research and capacity building (including training and education) efforts are essential to address knowledge gaps and effectively manage future OROV and MELV outbreaks in the Americas.

Oropouche virus (OROV) is an emerging orthobunyavirus responsible for widespread outbreaks across South and Central America. The recent surge in congenital infections has raised urgent concerns about OROV’s threat to maternal and fetal health. Here, we establish an in vivo model of OROV vertical transmission using the ancestral (prototype) strain BeAn19991 in immunocompetent C57BL/6J mice. We demonstrate that OROV efficiently replicates in maternal tissues, crosses the maternal–fetal interface, and infects both placental and fetal tissues. Parallel infections in human trophoblast-derived cell lines confirm conserved placental tropism across the ancestral strain and a contemporary (outbreak) isolate from the current outbreak. Importantly, we show that vertical transmission is not a recently acquired trait but a long-standing feature of OROV biology. Offspring born to infected dams mount neutralizing antibody responses and exhibit partial protection upon challenge. These findings conclusively confirm OROV as a vertically transmissible arbovirus, highlighting the urgent need to integrate OROV into surveillance, diagnostic, and vaccine preparedness efforts.

Oropouche virus (OROV) is a midge-borne human pathogen with a geographic distribution in South America. OROV was first isolated in 1955, and since then, it has been known to cause recurring outbreaks of a dengue-like illness in the Amazonian regions of Brazil. OROV, however, remains one of the most poorly understood emerging viral zoonoses. Here we describe the successful recovery of infectious OROV entirely from cDNA copies of its genome and generation of OROV mutant viruses lacking either the NSm or the NSs coding region. Characterization of the recombinant viruses carried out in vitro demonstrated that the NSs protein of OROV is an interferon (IFN) antagonist as in other NSs-encoding bunyaviruses. Additionally, we demonstrate the importance of the nine C-terminal amino acids of OROV NSs in IFN antagonistic activity. OROV was also found to be sensitive to IFN-α when cells were pretreated; however, the virus was still capable of replicating at doses as high as 10,000 U/ml of IFN-α, in contrast to the family prototype BUNV. We found that OROV lacking the NSm protein displayed characteristics similar to those of the wild-type virus, suggesting that the NSm protein is dispensable for virus replication in the mammalian and mosquito cell lines that were tested. Oropouche virus (OROV) is a public health threat in Central and South America, where it causes periodic outbreaks of dengue-like illness. In Brazil, OROV is the second most frequent cause of arboviral febrile illness after dengue virus, and with the current rates of urban expansion, more cases of this emerging viral zoonosis could occur. To better understand the molecular biology of OROV, we have successfully rescued the virus along with mutants. We have established that the C terminus of the NSs protein is important in interferon antagonism and that the NSm protein is dispensable for virus replication in cell culture. The tools described in this paper are important in terms of understanding this important yet neglected human pathogen.

Oropouche fever caused by Oropouche virus (OROV) is a significant zoonosis in Central and South America. Despite its public health significance, we lack high-throughput diagnostics, therapeutics, and a comprehensive knowledge of OROV biology. Reporter viruses are valuable tools to rapidly study virus dynamics and develop neutralization and antiviral screening assays. OROV is a tri-segmented bunyavirus, which makes generating a reporter virus challenging, as introducing foreign elements into the viral genome typically affects fitness. We previously demonstrated that the non-structural gene NSm on the OROV medium (M) segment is non-essential for replication in vitro. Taking advantage of this, we have now generated a recombinant OROV expressing fluorescent protein ZsGreen in place of NSm. This reporter OROV is both stable and pathogenic in IFNAR-/- mice and provides a powerful tool for OROV pathogenesis studies and assay development.IMPORTANCEEmerging and reemerging infectious agents such as zoonotic bunyaviruses are of global health concern. Oropouche virus (OROV) causes recurring outbreaks of acute febrile illness in the Central and South American human populations. Biting midges are the primary transmission vectors, whereas sloths and non-human primates are their reservoir hosts. As global temperatures increase, we will likely see an expansion in arthropod-borne pathogens such as OROV. Therefore, developing reagents to study pathogen biology to aid in identifying druggable targets is essential. Here, we demonstrate the feasibility and use of a fluorescent OROV reporter in mice to study viral dynamics and pathogenesis. We show that this reporter OROV maintains characteristics such as growth and pathogenicity similar to the wild-type virus. Using this reporter virus, we can now develop methods to assist OROV studies and establish various high-throughput assays.

Oropouche virus is an arthropod-borne virus that has caused outbreaks of Oropouche fever in central and South America since the 1950s. This study investigates virological factors contributing to the re-emergence of Oropouche fever in Brazil between 2023 and 2024. In this observational epidemiological study, we combined multiple data sources for Oropouche virus infections in Brazil and conducted in-vitro and in-vivo characterisation. We collected serum samples obtained in Manaus City, Amazonas state, Brazil, from patients with acute febrile illnesses aged 18 years or older who tested negative for malaria and samples from people with previous Oropouche virus infection from Coari municipality, Amazonas state, Brazil. Basic clinical and demographic data were collected from the Brazilian Laboratory Environment Management System. We calculated the incidence of Oropouche fever cases with data from the Brazilian Ministry of Health and the 2022 Brazilian population census and conducted age-sex analyses. We used reverse transcription quantitative PCR to test for Oropouche virus RNA in samples and subsequently performed sequencing and phylogenetic analysis of viral isolates. We compared the phenotype of the 2023-24 epidemic isolate (AM0088) with the historical prototype strain BeAn19991 through assessment of titre, plaque number, and plaque size. We used a plaque reduction neutralisation test (PRNT50) to assess the susceptibility of the novel isolate and BeAn19991 isolate to antibody neutralisation, both in serum samples from people previously infected with Oropouche virus and in blood collected from mice that were inoculated with either of the strains. 8639 (81·8%) of 10 557 laboratory-confirmed Oropouche fever cases from Jan 4, 2015, to Aug 10, 2024, occurred in 2024, which is 58·8 times the annual median of 147 cases (IQR 73-325). Oropouche virus infections were reported in all 27 federal units, with 8182 (77·5%) of 10 557 infections occurring in North Brazil. We detected Oropouche virus RNA in ten (11%) of 93 patients with acute febrile illness between Jan 1 and Feb 4, 2024, in Amazonas state. AM0088 had a significantly higher replication at 12 h and 24 h after infection in mammalian cells than the prototype strain. AM0088 had a more virulent phenotype than the prototype in mammalian cells, characterised by earlier plaque formation, between 27% and 65% increase in plaque number, and plaques between 2·4-times and 2·6-times larger. Furthermore, serum collected on May 2 and May 20, 2016, from individuals previously infected with Oropouche virus showed at least a 32-fold reduction in neutralising capacity (ie, median PRNT50 titre of 640 [IQR 320-640] for BeAn19991 vs <20 [ie, below the limit of detection] for AM0088) against the reassortant strain compared with the prototype. These findings provide a comprehensive assessment of Oropouche fever in Brazil and contribute to an improved understanding of the 2023-24 Oropouche virus re-emergence. Our exploratory in-vitro data suggest that the increased incidence might be related to a higher replication efficiency of a new Oropouche virus reassortant for which previous immunity shows lower neutralising capacity. São Paulo Research Foundation, Burroughs Wellcome Fund, Wellcome Trust, US National Institutes of Health, and Brazilian National Council for Scientific and Technological Development. For the Portuguese translation of the abstract see Supplementary Materials section.

Oropouche virus (OROV) is an emerging arbovirus in South and Central Americas with high spreading potential. OROV infection has been associated with neurological complications and OROV genomic RNA has been detected in cerebrospinal fluid from patients, suggesting its neuroinvasive potential. Motivated by these findings, neurotropism and neuropathogenesis of OROV have been investigated in vivo in murine models, which do not fully recapitulate the complexity of the human brain. Here we have used slice cultures from adult human brains to investigate whether OROV is capable of infecting mature human neural cells in a context of preserved neural connections and brain cytoarchitecture. Our results demonstrate that human neural cells can be infected ex vivo by OROV and support the production of infectious viral particles. Moreover, OROV infection led to the release of the pro-inflammatory cytokine tumor necrosis factor-alpha (TNF-α) and diminished cell viability 48 h post-infection, indicating that OROV triggers an inflammatory response and tissue damage. Although OROV-positive neurons were observed, microglia were the most abundant central nervous system (CNS) cell type infected by OROV, suggesting that they play an important role in the response to CNS infection by OROV in the adult human brain. Importantly, we found no OROV-infected astrocytes. To the best of our knowledge, this is the first direct demonstration of OROV infection in human brain cells. Combined with previous data from murine models and case reports of OROV genome detection in cerebrospinal fluid from patients, our data shed light on OROV neuropathogenesis and help raising awareness about acute and possibly chronic consequences of OROV infection in the human brain.

Oropouche virus (OROV) is an emerging arbovirus in South and Central Americas with high spreading potential. OROV infection has been associated with neurological complications and OROV genomic RNA has been detected in cerebrospinal fluid from patients, suggesting its neuroinvasive potential. Motivated by these findings, neurotropism and neuropathogenesis of OROV have been investigated in vivo in murine models, which do not fully recapitulate the complexity of the human brain. Here we have used slice cultures from adult human brains to investigate whether OROV is capable of infecting mature human neural cells in a context of preserved neural connections and brain cytoarchitecture. Our results demonstrate that human neural cells can be infected ex vivo by OROV and support the production of infectious viral particles. Moreover, OROV infection led to the release of the pro-inflammatory cytokine tumor necrosis factor-alpha (TNF-α) and diminished cell viability 48 h post-infection, indicating that OROV triggers an inflammatory response and tissue damage. Although OROV-positive neurons were observed, microglia were the most abundant central nervous system (CNS) cell type infected by OROV, suggesting that they play an important role in the response to CNS infection by OROV in the adult human brain. Importantly, we found no OROV-infected astrocytes. To the best of our knowledge, this is the first direct demonstration of OROV infection in human brain cells. Combined with previous data from murine models and case reports of OROV genome detection in cerebrospinal fluid from patients, our data shed light on OROV neuropathogenesis and help raising awareness about acute and possibly chronic consequences of OROV infection in the human brain.

In March 2024, the Pan American Health Organization (PAHO) issued an alert in response to a rapid increase in Oropouche fever cases across South America. Brazil has been particularly affected, reporting a novel reassortant lineage of the Oropouche virus (OROV) and expansion to previously non-endemic areas beyond the Amazon Basin. Utilising phylogeographic approaches, we reveal a multi-scale expansion process with both short and long-distance dispersal events, and diffusion velocities in line with human-mediated jumps. We identify forest cover, banana and cocoa cultivation, temperature, and human population density as key environmental factors associated with OROV range expansion. Using ecological niche modelling, we show that OROV circulated in areas of enhanced ecological suitability immediately preceding its explosive epidemic expansion in the Amazon. This likely resulted from the virus being introduced into simultaneously densely populated and environmentally favourable regions in the Amazon, such as Manaus, leading to an amplified epidemic and spread beyond the Amazon. Our study provides valuable insights into the dispersal and ecological dynamics of OROV, highlighting the role of human mobility in colonisation of new areas, and raising concern over high viral suitability along the Brazilian coast.