PORTLAND, Ore. (KOIN/AP) — A rare tropical disease that is spreading throughout parts of Latin America and the Caribbean is likely heading to the Americas, the World Health Organization announced Sunday.

The mosquito-borne Zika virus usually causes mild illness, but Brazilian officials say it’s associated with a recent wave of birth defects.

A female Aedes albopictus mosquito acquiring a blood meal from a human host. (James Gathany/Centers for Disease Control and Prevention via AP)

Now, health officials say the virus is likely to spread to every country in the Americas where the mosquito that carries it can be found. That includes every country except Canada and continental Chile.

Women in a number of Latin American countries are being asked to consider postponing pregnancies due to the Zika outbreak. U.S. health officials are also warning pregnant women to avoid traveling to 22 destinations affected by the virus:

Latin America: Bolivia, Brazil, Colombia, Ecuador, El Salvador, French Guiana, Guatemala, Guyana, Honduras, Mexico, Panama, Paraguay, Suriname and Venezuela.

In the Caribbean: Barbados, Guadeloupe, Haiti, Martinique, St. Martin and Puerto Rico. Also, Cape Verde, off the coast of western Africa; and Samoa in the South Pacific.

Mounting evidence links the Zika infection in pregnant women to a rare birth defect called microcephaly, in which a newborn’s head is smaller than normal and the brain may not have developed properly.

“Microcephaly, which means the brain has not developed adequately to make the brain casing — the skull — grow enough, and it’s not just 1 or 2 cases,” OHSU Dr. Aaron Caughey told KOIN 6 News. “They’ve described something in the several thousand cases, so it’s made everybody nervous enough to say ‘Hey, if you’re pregnant, if you don’t have to go to these countries, don’t go.'”

Dejailson Arruda holds his daughter Luiza at their house in Santa Cruz do Capibaribe, Pernambuco state, Brazil. (AP Photo/Felipe Dana)

The virus emerged in Africa in the 1940s, spread to Asia and was confirmed in the Americas only last May, though it likely appeared months earlier.

Some U.S. travelers have been infected abroad with Zika and other viruses spread by the Aedes aegypti mosquito, but there have been no cases of local infection with Zika in the U.S. so far.

Experts think most people infected with the Zika virus don’t get sick. Those who do usually develop mild symptoms like fever, rash, joint pain and red eyes that typically last no more than a week.

There is no specific medicine to treat the mosquito-borne virus and there hasn’t been a vaccine developed for it.

People can protect themselves from mosquito bites by using insect repellents and wearing long sleeves and long pants, especially during daylight when mosquitoes tend to be most active.The Associated Press contributed to this report