Insights into the expansion of Oropouche virus in Brazil: epidemiological and environmental aspects

Abstract

The Oropouche virus (OROV), an arbovirus transmitted primarily by the Culicoides paraensis midge, has caused significant outbreaks in the Americas, especially in the Amazon region. The virus's spread is closely linked to a combination of environmental, climatic, and ecological factors. These include deforestation, urbanization, and changes in rainfall patterns, which influence the proliferation of vectors, and, consequently, increase the chances of mutations and reassortment events to occur. In 2024 and 2025, the number of OROV cases increased significantly, with outbreaks extending beyond the traditionally endemic Amazon region, highlighting the growing geographic expansion of the disease throughout Brazil. Despite its growing dispersion, diagnostic and therapeutic tools for OROV remain limited. Current diagnostic strategies rely almost exclusively on molecular detection methods, and there are no vaccines for effective prevention. Additionally, immunological responses to OROV infection are not fully understood, and further studies are needed. The ecological dynamics influencing OROV transmission, particularly the role of environmental changes in shaping vector populations, highlight the need for more integrated surveillance and control strategies. The ongoing expansion of OROV outside its traditional hotspots may be indicative of broader environmental shifts that facilitate viral spread. Therefore, continuous monitoring of both environmental and epidemiological data is crucial to understanding and mitigating the impact of OROV in the future. Collaborative efforts among researchers, policymakers, and local communities will be essential to prevent further outbreaks and minimize the health burden caused by OROV. This review summarizes important and up-to-date data information to the ongoing epidemic of Oropouche fever, focusing on topics that are particularly important to Public Health.

Keywords: Culicoides paraensis; Oropouche fever; Orthobunyavirus oropoucheense; climate change; environmental impacts; epidemiology.

FIGURE 1

OROV transmission dynamics and main vectors. (A) Culicoides paraensis general aspect and taxonomic classification. Scale bar = 1 mm. Watercolor Illustration by F. da Fonseca. (B) Schematic representation of OROV transmission cycles. The sylvatic cycle involves primates, sloths, and other mammals as hosts, as well as some bird species (not shown). All possible arthropod vectors are not yet well known. The interaction between sylvatic and peri-urban environments primarily occurs due to deforestation and agricultural activities, which favor the transmission of diseases to humans. In the urban cycle, the virus is maintained by vectors such as Culicoides paraensis and possibly Culex quinquefasciatus, allowing dissemination in densely populated areas. Original figure created with Biorender.

FIGURE 2

Main symptoms of Oropouche fever. Oropouche fever is characterized by acute clinical symptoms, including high fever (above 39°C), intense headache, retro-orbital pain, myalgia, arthralgia, chills, general malaise, nausea, vomiting, diarrhea, and abdominal pain. Additionally, maculopapular rashes are common, typically starting on the trunk and spreading to the limbs. In some cases, hemorrhagic signs such as epistaxis, gum bleeding, and spontaneous bleeding may occur. Additional symptoms such as photophobia, dizziness, drowsiness, and a burning sensation are frequently observed, especially in more severe infections. Patients with severe forms of the disease may develop coagulopathies, hemorrhagic phenomena, acute kidney failure, and, in extreme cases, death. Infection may also affect the central nervous system, leading to meningitis or encephalitis. Original figure created with Biorender.

FIGURE 3

Geographical distribution of Oropouche fever cases in Brazil in 2024 and 2025. Confirmed cases of Oropouche fever in epidemiological week 1–52 of 2024 (left panel). Confirmed cases of Oropouche fever in epidemiological week 1–22 of 2025 (right panel). The Amazon region stands out in 2024, accounting for over 50% of the cases. The spread of the disease beyond the Amazon region reflects the geographical expansion of the disease. In 2025, the state of Espírito Santo accounted for the majority of cases, indicating an early epicenter outside the Amazon region. Epidemiological data on OROV in Brazil were obtained from the Brazilian Ministry of Health [67].

FIGURE 4

Projection of OROV case numbers across the four-quarters of 2024 concerning temperature and accumulated precipitation. (A,E) Relationship between temperature and number of cases in the first trimester/relationship between precipitation accumulation and number of cases in the first trimester. (B,F) Relationship between temperature and number of cases in the second trimester/relationship between precipitation accumulation and number of cases in the second trimester. (C,G) Relationship between temperature and number of cases in the third trimester/relationship between precipitation accumulation and number of cases in the third trimester. (D,H) Relationship between temperature and number of cases in the fourth trimester/relationship between precipitation accumulation and number of cases in the fourth trimester. The color scale determines the temperature gradient (A–E) and the accumulated precipitation gradient (F–G), and the size of the circles represents the number of cases.