A virus spread by tiny insects is on the rise in Brazil and Cuba. Here's how to protect yourself

Canadians flying to popular locales like Cuba are being warned to take precautions against insects that spread the rare and potentially deadly Oropouche virus, also called Oropouche fever.

This week, U.S. officials announced 21 cases of Oropouche virus disease among travellers returning from Cuba as of Aug. 16. Most got better without treatment, while three patients recovered after hospitalization.

The virus is most commonly spread through bites from some types of midges (and some mosquitoes) that are not found in Canada. 

But doctors here are asked to watch for infections in returning travellers. While Oropouche virus disease has previously been found to circulate in Central and South America as well as in the Caribbean, this year's cases have been higher than expected, with human infections reported in places they haven't been detected before, in new areas of Brazil, Bolivia and Cuba.

It's unclear how the virus impacts the health of a fetus, and precautions are recommended during pregnancy. 

"It's generally historically been reported as fairly mild, but with some of this emerging data around neurologic complications and even fatality — it's something that needs to be watched," said Dr. Zain Chagla, an infectious diseases physician and associate professor of medicine at McMaster University who has tropical medicine training.

"These are areas of the world where Canadians visit, and even though there's not local circulation [in mosquitoes], it still means that travellers are going to have to be assessed for this as they return," Chagla said.

Here's a look at the illness that's sparked updated travel health alerts in Canada, the U.S. and Europe.

Oropouche virus is endemic or naturally occurring in forested tropical areas. It was first identified in 1955 on the island of Trinidad and takes its name from a nearby village and wetlands.

It has sometimes been called sloth fever, since it was first detected in Brazil from a blood sample taken from the animal.

The Oropouche virus is mainly spread through the bite of a tiny fly known as a midge, often called "no-see-ums," as well as some types of mosquitoes.

"While the species of midge (Culicoides paraensis) and mosquito (Culex quinquefasciatus) that are known to transmit Oropouche virus disease are not known to be established in Canada, they have been detected in the United States," the Public Health Agency of Canada (PHAC) said in response to questions from CBC News.

Scientists say high temperatures, humidity and the season affect the midge populations.

Human-to-human transmission hasn't been documented.