Brazil, which has recently suffered serious outbreaks of Zika virus and yellow fever, now faces a new threat, according to reports from local scientists: Oropouche fever.
The Oropouche virus, named for a river in Trinidad, where it was first isolated in 1955, circulates in monkeys and sloths in the Amazon jungle. The virus has caused occasional outbreaks, short but intense, in towns in tropical areas of Brazil, Peru and Panama, and on some Caribbean islands.
But in the last few years, Oropouche cases have turned up more often in urban areas, including some in northeast Brazil, where Zika began its explosive spread in this hemisphere.
Oropouche causes symptoms resembling those of dengue: high fever, headaches and joint pain, nausea and malaise. The infection is not normally fatal, although it can cause meningitis — dangerous brain stem swelling — if it reaches the spinal fluid. There is no vaccine.
The virus is typically transmitted by a biting midge, Culicoides paraensis, that ranges from Argentina to as far north as Wisconsin. The insects are known variously as no-see-ums, because of their size, or gunpowder midges, because they resemble black gunpowder grains.
Smaller than mosquitoes, they can slip through some screens; their sharp bites raise small, intensely itchy bumps.
In a statement by the São Paulo Research Foundation, picked up by American disease-alert news services, Dr. Luiz Tadeu Moraes Figueiredo, an emerging-disease specialist at the University of São Paulo, warned that Oropouche could soon be a serious public health problem in Brazil.
In the Brazilian news media, Dr. Figueiredo has been quoted saying Oropouche can also be spread by Aedes aegypti mosquitoes, which infest the country’s vast urban slums. The mosquitoes aggressively bite humans, transmitting Zika, dengue, yellow fever and chikungunya.
Since the 1980s, the Oropouche virus has occasionally been detected in both Culex and Aedes mosquitoes in forests, but it is not clear that these insects were involved in any human outbreaks.