LONDON -- The World Health Organization says women in countries hit by the Zika virus should breastfeed their babies and there is no proof the disease can spread to their infants that way.

Zika has been declared a global emergency because of its links to a spike in babies born with abnormally small heads in Brazil and an increase in cases of a rare syndrome that can cause paralysis. Brazil has more than 1 million infections and the virus, which is now found in 36 countries, is exploding across the Americas.

In guidance issued Thursday, WHO said while Zika has been detected in breast milk from two mothers, there are no reports of Zika being transmitted to babies via breastfeeding.

But the U.N. health agency acknowledged there were many unanswered questions, including how much Zika virus is contained in breast milk, whether mothers may pass on protective antibodies to their children from a previous Zika infection and how long the virus might persist in breast milk.

WHO said there have been no cases of babies suffering severe neurological problems or brain damage after being infected with Zika after birth. The agency said its current breastfeeding recommendations remain valid despite Zika's alarming spread.

"The benefits of breastfeeding for the infant and mother outweigh any potential risk of Zika virus transmission through breast milk," WHO said.

Zika is mostly spread to people by mosquito bites, although there have been rare cases of sexual transmission. WHO has also warned that Zika "may present a risk to blood safety" and noted two probable cases of Zika spread by blood transfusions.

Until recently, WHO recommended that women with HIV -- which is spread by bodily fluids -- avoid breastfeeding, although they now say the risk can be managed if a woman takes antivirals.

WHO said it will review the latest evidence next month to update these recommendations.