Brazilian Army soldiers distribute pamphlets with information to combat the Aedes aegypti mosquito during the National Day of Mobilization Zika Zero at Central train station in Rio de Janeiro, Brazil, February 13, 2016. [Photo/Agencies]

GENEVA - The World Health Organization (WHO) called on Wednesday for $56 million to combat the Zika virus, a disease that has been linked to severe birth defects in Brazil and has spread to 39 other countries.

The funds sought would be used until June to fast-track vaccines, carry out diagnostics and research into how the mosquito-borne virus spreads, as well as virus control, the WHO said.

A public health expert, Lawrence Gostin, said the United Nations health agency had "grossly underestimated" the need as the virus, which has spread rapidly across the Americas, will likely spread to many other regions.

The WHO declared the outbreak a global public health emergency on Feb. 1, noting the association of the virus with two neurological disorders: microcephaly in babies and Guillain-Barre syndrome that can cause paralysis.

"Possible links with neurological complications and birth malformations have rapidly changed the risk profile for Zika from a mild threat to one of very serious proportions," WHO Director-General Margaret Chan said in a WHO strategy paper on Wednesday.

The funds sought include $25 million for the agency and its regional office and the rest for aid partners such as UNICEF. The WHO expects the money to come from states and other donors. In the meantime it has tapped a new emergency contingency fund for $2 million for initial operations.

Gostin, a professor at Georgetown University in Washington, said the WHO should have a much larger emergency contingency fund. He compared the funding plan to the WHO's initial slow response to the outbreak of Ebola, a virus that killed more than 11,300 people in two years, mostly in West Africa.