Ilhéus virus

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Ilhéus virus (ILHV) is a positive‑sense RNA virus in the Flaviviridae family. It was first found in 1944 in mosquitoes in Ilhéus, Bahia, Brazil, and it is now known to be widespread in much of South and Central America and the Caribbean.

Vectors and transmission
ILHV is carried mainly by mosquitoes. Aedes and Culex species are among the insects involved, but other mosquito genera can also harbor the virus. Some studies suggest Aedes mosquitoes may be more important in spreading ILHV than previously thought, while the common mosquito Culex quinquefasciatus might be resistant.

Host range and cycles
The virus is believed to maintain itself in a cycle involving Culex mosquitoes and wild birds, but it can also infect a wide range of animals, including monkeys, coatis, sloths, horses, rodents, bats, and tortoises, as well as humans. It is not always clear whether these other animals can pass the virus back to mosquitoes.

Disease in humans
Ilhéus fever is the illness caused by ILHV in people. It typically presents with fever, muscle pain, headache, and general malaise, and can also include encephalitis (brain inflammation), joint pain, cough, and diarrhea. Because these symptoms resemble many other febrile illnesses, ILHV infections are often missed or mistaken for something else. Most infections are mild or asymptomatic, but rare cases of severe illness, including encephalitis and brain hemorrhage, have been reported.

Outlook and concern
ILHV can replicate quickly in mammalian cells, which raises concern about the potential for spillover to humans, especially as people encroach on wild habitats in the Neotropics. While ILHV has not caused widespread outbreaks, its close relatives have caused significant disease in the past, highlighting the importance of monitoring and controlling mosquito exposure.