The world’s first deaths from Oropouche fever, a mosquito-borne virus, have been recorded in Brazil, sparking alarm among scientists. Brazilian authorities reported the deaths of two women, aged 21 and 24, on July 25. Both women experienced severe abdominal pain, bleeding, and hypotension.
Prior to these fatalities, no deaths from Oropouche fever had been documented in scientific literature, as confirmed by Brazil’s Ministry of Health. The cases occurred in Bahia state, far from the Amazon rainforest where the virus is typically found.
Eurico Arruda, a virology professor at the University of Sao Paulo, emphasized the gravity of these deaths: “No mortality had been recorded—these deaths change history. The virus, which used to circulate almost exclusively in the Amazon region, is now circulating in other regions, and this is very worrying.”
Discovered in 1955 in Trinidad and Tobago, the Oropouche virus has since infected approximately half a million people, mainly in the Amazon basin. However, the virus has now spread beyond its traditional confines. In 2024, 7,236 cases were confirmed across 20 Brazilian states, a stark rise from 835 cases in 2023.
The disease typically presents symptoms similar to dengue and chikungunya, including sudden fever, headache, muscle, and joint pain. However, Arruda, who has studied the virus for three decades, suggests that a deadly mutation may have emerged through recombination, wherein two strains infect the same cell and produce a new, more aggressive virus.
This possibility was explored in a recent study by Brazilian scientists, which linked a new strain of the virus to a 2022 outbreak in the western Amazon. The study, which analyzed the Oropouche virus genome in 383 samples from 2022 to 2024, found that the new strain combined segments from various geographical origins, resulting in a genetic rearrangement.
Felipe Naveca, head of the Laboratory of Arboviruses and Hemorrhagic Viruses at the Oswaldo Cruz Institute, indicated that the Bahía cases are likely connected to this new strain. “The deaths demonstrate that infection by the virus can be lethal, confirming previous suspicions. But it is necessary to further investigate the exact mechanism by which this occurs.”
The study, published as a preprint in the MedRxiv repository, suggests that the virus’s spread was influenced by factors like mosquito movement, human travel, deforestation, agricultural invasion, and extreme weather events such as El Niño.
The virus’s silent spread from the Brazilian Amazon to other regions and countries has been particularly concerning. Outbreaks have already been recorded in Bolivia, Cuba, Colombia, French Guiana, and Peru. Additionally, a report by the European Centre for Disease Prevention and Control noted that Italy and Spain reported three cases in travelers returning from Cuba.
The virus’s ability to pass through the placenta and infect fetuses has led to six cases of mother-to-child transmission in Brazil. These included two fetal deaths, one miscarriage, and three cases of congenital abnormalities such as microcephaly.
The potential adaptation of the virus to urban mosquitoes, such as Aedes aegypti, remains a significant concern. “The situation is worrying because there is no vaccine or specific treatment,” Arruda stated.
International scientists recently convened at the University of Leeds in the UK to address this emerging threat, aiming to develop a rapid diagnostic method and test potential treatments for Oropouche fever.