New study in Nature Ecology & Evolution on the dynamics and ecology of the Oropouche virus expansion in Brazil

Published on April 16, 2026, by Simon Dellicour

In March 2024, Brazil reported an unprecedented Oropouche fever outbreak, driven by the emergence of a novel reassortant lineage of the Oropouche virus expanding beyond the Amazon Basin. Oropouche virus (OROV) is an arthropod-borne virus first identified in 1955 in Oropouche, a village in Trinidad and Tobago. OROV typically causes a febrile illness with symptoms such as fever, headache, myalgia, arthralgia, photophobia, nausea, vomiting, and dizziness. In some cases, the illness can progress to severe neurological complications, including meningo-encephalitis.

To investigate the expansion dynamics of OROV, we implemented complementary phylogeographic and ecological niche modelling approaches that aimed to characterise the environmental factors associated with the range expansion and the risk of local circulation, respectively. Our analyses reveal a multi-scale expansion process with both short and long-distance dispersal events, and diffusion velocities in line with air traffic-mediated jumps. We identify banana and cocoa cultivation, temperature, the predicted suitability of the primary vector Culicoides paraensis, and human population density as key environmental factors associated with OROV range expansion in new areas. We further show that OROV circulated in areas of enhanced ecological suitability immediately preceding its explosive epidemic expansion in the Amazon. Our study provides valuable insights into the dispersal and ecological dynamics of OROV, highlighting the likely role of human mobility in the long-distance colonisation of new areas, and raising concern over high viral suitability along the Brazilian coast. Read the whole study here.

Figure 1. Dispersal history and dynamics of OROV lineages in Brazil. (A) Dispersal history of OROV lineages inferred through continuous phylogeographic reconstructions. Lineage dispersal events between Brazilian states with a posterior probability ≥0.95 are displayed by solid arrows, and dispersal events with a posterior probability <0.95 are displayed by dashed arrows. Additionally, the location of the different areas is represented by transparent grey dots whose surface is proportional to the number of local lineage dispersal events, i.e. phylogenetic branches inferred as remaining in that state. Brazilian states are coloured according to the estimated date of the first invasion event (median date computed from the 100 trees sampled from the posterior distribution), and are labelled with their abbreviated names (AM: Amazonas, AC: Acre, RO: Rondonia, MT: Mato Grosso, MG: Minas Gerais, BA: Bahia, SC: Santa Catarina). Time to the most recent sampling ancestor (tMRCA) estimated for each segment are associated with large and overlapping 95% highest posterior density (HPD) intervals: from March 2017 to September 2020 for segment L, from August 2016 to December 2019 for segment M, and from July 2015 to April 2018 for segment S. (B) Evolution through time of the spatial wavefront distance, representing the maximal distance from the epidemic origin over time. The solid curve corresponds to the median estimate and the surrounding ribbon - coloured according to time - to the corresponding 95% highest posterior density (HPD) interval. (C) Evolution through time of the weighted diffusion coefficient, a dispersal metric that measures the dispersal capacity of viral lineages. As in panel B, the solid curve corresponds to the median estimate and the surrounding ribbon to the 95% HPD interval. (D) Kernel density plots with the branch-weighted diffusion coefficient against the geographic distance travelled by each branch (both axes being log-transformed).

Reference: Tegally H*, Dellicour S*, Poongavanan J*, Mavian C*, Dor G, Fonseca V, Tagliamonte M, Dunaiski M, Moir M, Wilkinson E, Melo CF, Vinhal Frutuoso LC, Holmes E, Baxter C, Lessells R, Kraemer MUG, Lourenço J, Alcantara L, de Oliveira T, Giovanetti M (2026). Dynamics and ecology of a multi-stage expansion of Oropouche virus in Brazil. Nature Ecology & Evolution, in press