Health officials around the world are on high alert after the Zika virus, which has been around for decades, has suddenly become the source of an outbreak, and three cases, including one in Calgary, have made it to Canada.

The mosquito-borne Zika virus only posed a mild threat until a wide number of cases of the illness were recently discovered in Brazil.

Three Canadians, including one Calgarian, have now contracted the disease, which only has mild symptoms such as fever, rash, red eyes, and joint pain which lasts from several days to a week.

But the bigger concern is the threat posed to pregnant women or women at risk of being pregnant.

Zika can cause micro encephalitis, a condition that results in babies being born with abnormally small head and brains, and brain damage.

Mosquitoes carrying the disease aren’t able to survive in Canada, but they are spreading in Central and South America.

The World Health Organization says that Zika could end up infecting four million people in those areas as well as the Caribbean by next year.

“It is now spreading explosively,” said Dr. Margaret Chan with the WHO. “As of today, cases have been reported in 23 countries.”

While Alberta Health Services haven’t confirmed the findings, an infectious disease expert CTV spoke to on Thursday says there is a case in the city.

“Calgary had another case just a couple weeks ago,” said Stan Houston, a professor of medicine and public health at the University of Alberta. “These are returned travelers.”

“If you’re pregnant or at risk of being pregnant, you should avoid endemic areas. If you have to go, be super strict about preventing exposure.”

Experts say the best way is to avoid being bitten by wearing insect repellent with DEET and cover up exposed skin.

A Calgary restaurant manager, whose parents and sister live in Brazil, says he is very concerned about the disease, especially with many of his staff visiting the South American country.

“It’s about time that it will be spearing through the country, and we are worried about family and friends that are there. We are here, calling them and making sure they are okay,” said Evandro Pelegrini, front house manager of Gaucho Brazilian BBQ.

Pelegrini says he is not planning on travelling back there anytime soon. “I feel for my family that is all there, but here in Canada I think we’re safe for now.”

There is some concern that the Zika virus can be spread through blood, so the Canadian Blood Services says it is considering changes to some policies, such as denying donations from anyone who have recently visited the affected countries.

Canadian airlines are also allowing passengers to change their bookings to Central and South America to avoid those countries.

Refunds and changes will be made under certain conditions.

(With files from Ina Sidhu)