A list of tropical destinations with Zika virus infections expanded to eight more places, the U.S. Centers for Disease Control and Prevention says.

The CDC updated its travel alert on Friday to 22 countries and regions, adding Barbados, Bolivia, Ecuador, Guadeloupe, Saint Martin, Guyana, Cape Verde, and Samoa.

About 80 per cent of those infected have no symptoms. The virus, which is spread by day-biting mosquitoes, can cause fever, rash, joint pain and red eyes.

In Brazil, the Zika virus has been associated with a large increase in the number of cases of microcephaly — babies born with abnormally small heads and underdeveloped brains.

Canadian and American health officials say pregnant women and those trying to conceive consider postponing travel to areas where the virus is circulating.

Zika virus

An army soldier checks for mosquito larvae to try to limit transmission of the Zika virus in Sao Paulo, Brazil. (Miguel Schincariol/AFP/Getty)

Such women should also talk to their health care provider to assess their risk and strictly follow precautions to avoid mosquito bites if they can't postpone the trip.

On Friday, Brazilian researchers writing in the CDC's Morbidity and Mortality Weekly Report provided some details on 35 infants with microcephaly born to women who lived or travelled to areas where the virus circulates.

Meanwhile in El Salvador, health officials are piecing together whether the virus is also associated with a jump in cases of Guillain Barré syndrome. The nerve disease leads to tingling or weakness in the legs, muscular weakness and progressive paralysis.

Guillain-Barré usually occurs a few days or weeks after someone has had symptoms of a respiratory or gastrointestinal viral infection, the U.S. National Institutes of Health says.

The syndrome has also been reported in patients with probable Zika virus infection in French Polynesia and Brazil, the CDC says. 

With files from The Associated Press