There is "accumulating evidence" of a link between the Zika virus and two neurological disorders, microcephaly and Guillain-Barre syndrome, says the World Health Organisation.
The WHO's Emergency Committee will meet next week to review "evolving information" and its recommendations on travel and trade in what is thought to be high season for transmission of the mosquito-borne virus in the southern hemisphere, it said on Friday.
Dr Bruce Aylward, WHO Executive Director for Outbreaks and Health Emergencies, said that recently published studies in the Lancet on microcephaly and by the US Centers for Disease Control (CDC) on Guillain-Barre had strengthened the case that the Zika virus is responsible.
"Since the public health emergency of international concern was declared (by WHO) back in February, the evidence that there may be a causal relationship has continued to accumulate," Aylward told a news briefing in Geneva.
French scientists, in a retrospective study of a Zika outbreak in French Polynesia in 2013-2014, said last week they had proved a link between Zika and Guillain-Barre, suggesting countries hit by the Zika epidemic will see a rise in cases of the serious neurological condition.
A study of nine pregnant women from the United States who travelled to countries where the Zika virus was circulating showed a greater-than-expected number of fetal infections and brain abnormalities, US health officials said last week.
Much remains unknown about Zika, including whether the virus actually causes microcephaly in babies, a condition defined by unusually small heads that can result in developmental problems.
Brazil said it has confirmed more than 640 cases of microcephaly, and considers most of them to be related to Zika infections in the mothers. Brazil is investigating more than 4200 additional suspected cases of microcephaly.
"We're now in the high season for dengue virus transmission in the southern hemisphere, that started a month or so ago. We believe because it's the same vector, that this would be the high season obviously for Zika transmission as well," Aylward said.
