Re-emerging Oropouche virus infections: insights into maternal-fetal crosstalk, coinfections, and expanding public health threats.

Purpose To synthesize current evidence on Oropouche virus infection during pregnancy, with particular emphasis on transmission dynamics, clinical presentation, diagnostic challenges, and emerging data on vertical transmission and adverse fetal and perinatal outcomes. Materials and Methods A narrative review of the literature was conducted to summarize available data on Oropouche virus infection in pregnancy. Searches were performed in PubMed/MEDLINE, Scopus, Web of Science, Embase, SciELO, and LILACS, complemented by official reports from the World Health Organization (WHO), Pan American Health Organization (PAHO), Centers for Disease Control and Prevention (CDC), and the Brazilian Ministry of Health. The search strategy included combinations of the following keywords: “Oropouche virus”, “Oropouche fever”, “pregnancy”, “vertical transmission”, “congenital infection”, “fetal outcomes”, “arbovirus”, and “perinatal outcomes”. Original studies, case reports, case series, reviews, surveillance reports, and clinical guidelines published in English, Portuguese, or Spanish were considered. No formal quality assessment or meta-analysis was performed, consistent with a narrative review design. Results Oropouche virus is an emerging arboviral infection in Latin America, with a rapidly increasing number of cases reported in Brazil and neighboring countries. Transmission occurs mainly via Culicoides paraensis midges and Culex mosquitoes. Although infection is usually self-limiting, clinical manifestations frequently overlap with other arboviral diseases, complicating diagnosis. Growing evidence indicates that vertical transmission can occur, with confirmed cases associated with fetal demise and congenital anomalies, including microcephaly, ventriculomegaly, corpus callosum dysgenesis, cerebral atrophy, posterior fossa abnormalities, and arthrogryposis. Viral neurotropism and detection of viral RNA in placental and fetal tissues support a plausible teratogenic potential. Diagnostic confirmation relies on RT-PCR during the acute phase and serological testing thereafter. In pregnancy, management requires referral to high-risk obstetric care, serial fetal imaging, particularly focused on central nervous system evaluation, and multidisciplinary perinatal planning. Conclusion Oropouche virus infection should be recognized as an emerging threat to maternal and fetal health. Accumulating evidence of vertical transmission and congenital involvement underscores the need to include Oropouche virus in the differential diagnosis of febrile illness during pregnancy in endemic areas. In the absence of specific treatment or licensed vaccines, prevention relies on vector control and personal protective measures. Strengthened surveillance systems, standardized diagnostic protocols, and prospective studies are urgently needed to clarify the magnitude of fetal risk, mechanisms of vertical transmission, and long-term outcomes of congenitally exposed infants.

Interferon (IFN)-regulatory factor 5 (IRF-5) is a transcription factor that induces inflammatory responses after engagement and signaling by pattern recognition receptors. To define the role of IRF-5 during bunyavirus infection, we evaluated Oropouche virus (OROV) and La Crosse virus (LACV) pathogenesis and immune responses in primary cells and in mice with gene deletions in Irf3, Irf5, and Irf7 or in Irf5 alone. Deletion of Irf3, Irf5, and Irf7 together resulted in uncontrolled viral replication in the liver and spleen, hypercytokinemia, extensive liver injury, and an early-death phenotype. Remarkably, deletion of Irf5 alone resulted in meningoencephalitis and death on a more protracted timeline, 1 to 2 weeks after initial OROV or LACV infection. The clinical signs in OROV-infected Irf5(-/-) mice were associated with abundant viral antigen and terminal deoxynucleotidyltransferase-mediated dUTP-biotin nick end labeling (TUNEL)-positive cells in several regions of the brain. Circulating dendritic cell (DC) subsets in Irf5(-/-) mice had higher levels of OROV RNA in vivo yet produced lower levels of type I IFN than wild-type (WT) cells. This result was supported by data obtained in vitro, since a deficiency of IRF-5 resulted in enhanced OROV infection and diminished type I IFN production in bone marrow-derived DCs. Collectively, these results indicate a key role for IRF-5 in modulating the host antiviral response in peripheral organs that controls bunyavirus neuroinvasion in mice. Oropouche virus (OROV) and La Crosse virus (LACV) are orthobunyaviruses that are transmitted by insects and cause meningitis and encephalitis in subsets of individuals in the Americas. Recently, we demonstrated that components of the type I interferon (IFN) induction pathway, particularly the regulatory transcription factors IRF-3 and IRF-7, have key protective roles during OROV infection. However, the lethality in Irf3(-/-) Irf7(-/-) (DKO) mice infected with OROV was not as rapid or complete as observed in Ifnar(-/-) mice, indicating that other transcriptional factors associated with an IFN response contribute to antiviral immunity against OROV. Here, we evaluated bunyavirus replication, tissue tropism, and cytokine production in primary cells and mice lacking IRF-5. We demonstrate an important role for IRF-5 in preventing neuroinvasion and the ensuing encephalitis caused by OROV and LACV.

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.

Re-emergence of Oropouche virus between 2023 and 2024 in Brazil: an observational epidemiological study

Oropouche virus (OROV), a neglected arbovirus, has historically been considered a self-limiting infection associated with febrile illness. However, the recent surge in cases since late 2023 has been marked by atypical outcomes, highlighting its underestimated clinical impact. Gastrointestinal symptoms such as diarrhea have also been reported, but the prevalence and mechanistic insight remain largely elusive. Here, through a meta-analysis of 12 identified clinical studies, we revealed a pooled prevalence of diarrhea as 15% (95% CI, 10%-20%) among the Oropouche patient population. In primary human intestinal organoid-based experimental models, we demonstrated productive infection by both a recent patient isolate (OROV-2024) and a historical strain (Be An19991). This is shown by the accumulation of intracellular OROV RNA, release of infectious particles, and immunostaining of OROV glycoprotein Gc. Interestingly, OROV infection mildly triggered the expression of type III interferons, but this endogenous response was insufficient to limit viral replication. In contrast, exogenous treatment with type I and III interferons strongly inhibited OROV replication, with interferon-alpha completely abolishing infectious virus production. Together, these results suggest the human intestine as a potential target organ for OROV infection and highlight interferons as potential therapeutic candidates.IMPORTANCEOropouche virus (OROV) is an emerging arbovirus with rapidly increasing incidence and recent reports of severe disease outcomes. While gastrointestinal symptoms have been described, the intestinal tropism of OROV has not been experimentally explored. By combining meta-analysis of clinical data with human intestinal organoid infection models, we demonstrate that OROV can replicate in intestinal epithelial cells. We further show that, in a human intestinal organoid model, endogenous interferon responses are insufficient to restrict replication, while treatment with interferons exerts potent antiviral activity. These findings highlight the susceptibility of intestinal epithelial cells to OROV infection and the therapeutic potential of interferons.

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 2024 Oropouche virus (OROV) outbreak in Brazil raised public health concerns due to its unprecedented rapid spread, high incidence, and potential neurological complications. OROV symptoms overlap with locally endemic arbovirus diseases, like dengue virus (DENV), complicating diagnosis. The study aimed to compare clinical, laboratory, and immunological profiles in OROV and DENV cases, crucial for improving diagnosis and management. This study analyzed 51 OROV and 78 of DENV cases consecutively enrolled in Manaus, Amazonas, Brazil, and monitored for 28 days. OROV diagnosis was performed by real-time PCR (RT-PCR) using serum and urine samples. OROV RT-PCR positive samples were genotyped. A paired Plaque Reduction Neutralization Test (PRNT) was conducted on samples collected at D1 and D28. Patients with a ≥ 4-fold increase in neutralizing antibody titer between D1 and D28 were considered OROV-positive. Clinical manifestations, hematology, biochemistry, and cytokine profiles were analyzed. Statistical analysis included comparison between OROV and DENV patients. Genome sequencing of OROV isolates confirmed presence of a previously reported novel reassortment event, consistent with ongoing localized transmission. Urine RT-PCR demonstrated low positivity compared to serum samples. The paired PRNT increased sensitivity in 45%. Clinically, OROV infection was associated with significantly higher frequencies of severe headache, myalgia, arthralgia, and rash compared to DENV infection (p < 0.001). Elevated alanine aminotransferase (ALT) levels were also observed in OROV patients (p < 0.001). Immunologically, OROV infection induced significantly increased levels of acute-phase CCL11 (eotaxin), CXCL10, IFN-γ, IL-1RA, and IL-10, which declined by day 28, while IL-5 increased during recovery. In contrast, DENV patients exhibited elevated levels of CCL2, G-CSF, and CCL3 in recovery phase. OROV symptoms overlap with DENV underscores the need for syndromic diagnostic approach in endemic regions. Continued genomic surveillance and expanded clinical studies are vital to assess long-term consequences. Given OROV's expanding geographic range, targeted public health measures are essential to mitigate future outbreaks and better understand its pathophysiology.

Oropouche Fever Outbreak, Manaus, Brazil, 2007–2008

BackgroundThe 2024 Oropouche virus (OROV) outbreak in Brazil raised public health concerns due to its unprecedented rapid spread, high incidence, and potential neurological complications. OROV symptoms overlap with locally endemic arbovirus diseases, like dengue virus (DENV), complicating diagnosis. The study aimed to compare clinical, laboratory, and immunological profiles in OROV and DENV cases, crucial for improving diagnosis and management.MethodsThis study analyzed 51 OROV and 78 of DENV cases consecutively enrolled in Manaus, Amazonas, Brazil, and monitored for 28 days. OROV diagnosis was performed by real-time PCR (RT-PCR) using serum and urine samples. OROV RT-PCR positive samples were genotyped. A paired Plaque Reduction Neutralization Test (PRNT) was conducted on samples collected at D1 and D28. Patients with a ≥ 4-fold increase in neutralizing antibody titer between D1 and D28 were considered OROV-positive. Clinical manifestations, hematology, biochemistry, and cytokine profiles were analyzed. Statistical analysis included comparison between OROV and DENV patients.ResultsGenome sequencing of OROV isolates confirmed presence of a previously reported novel reassortment event, consistent with ongoing localized transmission. Urine RT-PCR demonstrated low positivity compared to serum samples. The paired PRNT increased sensitivity in 45%. Clinically, OROV infection was associated with significantly higher frequencies of severe headache, myalgia, arthralgia, and rash compared to DENV infection (p < 0.001). Elevated alanine aminotransferase (ALT) levels were also observed in OROV patients (p < 0.001). Immunologically, OROV infection induced significantly increased levels of acute-phase CCL11 (eotaxin), CXCL10, IFN-γ, IL-1RA, and IL-10, which declined by day 28, while IL-5 increased during recovery. In contrast, DENV patients exhibited elevated levels of CCL2, G-CSF, and CCL3 in recovery phase.ConclusionOROV symptoms overlap with DENV underscores the need for syndromic diagnostic approach in endemic regions. Continued genomic surveillance and expanded clinical studies are vital to assess long-term consequences. Given OROV’s expanding geographic range, targeted public health measures are essential to mitigate future outbreaks and better understand its pathophysiology.

The discovery that the Oropouche virus (OROV) can be transmitted vertically from an infected pregnant mother to the fetus, resulting in fetal and placental OROV infection, miscarriage, stillbirth, and congenital malformations including microcephaly, has emphasized its public health significance. Because of the importance of breastfeeding in those areas affected by the Oropouche fever outbreak, public health agencies have continued to encourage nursing among mothers who have had OROV infection or who reside or travel in endemic regions. However, the basis for this recommendation has not been stated. At the present time, there have been no reports of the OROV being transmitted from mothers having had Oropouche fever during pregnancy to their infants through breast milk. To further evaluate the potential risk of OROV transmission through breastfeeding, we have examined the peer-reviewed literature to determine if related Orthobunyavirus species infecting humans and animals are transmissible via breast milk. Bibliographic search engines, including PubMed, Scopus, and Google Scholar, were extensively reviewed using keywords, MeSH terms, and other sources cited in the articles examined. Studies investigating Orthobunyavirus species that infect humans and animals, including reassortant strains of OROV and viruses within the Simbu serogroup, were reviewed. We found that there have been no reported events of vertical transmission of any Orthobunyavirus through breast milk. Based on these results, we believe that the advantages of breastfeeding following maternal OROV infection outweigh any negligible risk for vertical transmission.

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.

Oropouche virus (OROV) is emerging as a growing public health concern, with increasing numbers of case, an expanding global spread and the potential for severe clinical outcomes. However, despite the increasing incidence, the clinical features of OROV infections have not yet been thoroughly examined. The present systematic review and meta-analysis aimed to investigate the prevalence of clinical manifestations in OROV infections. For this purpose, a comprehensive search across PubMed, Web of Science and Embase was conducted up to April 9, 2025, to identify relevant studies. A random effects model was employed to calculate the pooled prevalence and 95% confidence intervals were calucalted. Heterogeneity was assessed using the I2 statistic. Additionally, sensitivity analyses and publication bias assessments were conducted to ensure the robustness of our findings. The present study included 28 articles and assessed 4,196 patients with OROV infection from 6 countries across the globe. The pooled prevalence of clinical manifestations of OROV included fever (97%), headache (86.5%), myalgia (72.3%), malaise or fatigue (56.4%), arthralgia (50.3%), chills (49.6%), loss of appetite (44.3%), eye pain (43.2%), back pain (31.7%), pallor (31.7%), dizziness (30.2%), photophobia (30.9%), nausea/vomiting (28.9%), sore throat (26.1%), odynophagia (22.9%), diarrhea (18.4%), skin rash (18.2%), conjunctival injection (15.4%), abdominal pain (16.3%), petechiae (2.3%), cough (12.9%), and chest pain (0.7%). High heterogeneity was detected among the included studies, which may be attributed to differences in geographic locations and diagnostic methodologies. Sensitivity analyses further supported the robustness of our findings. On the whole, the present systematic review provides a comprehensive analysis of the clinical manifestations of OROV infection, highlighting key symptoms that may aid in differential diagnosis in arbovirus-endemic regions. The findings may provide critical insight for clinicians and public health professionals and lay the groundwork for future research on the pathogenesis and epidemiology of OROV.

Cytokine profiling in oropouche fever highlights dissociation between systemic immunity and viral load.

Oropouche virus infection induces pyroptosis in human THP-1 macrophages.