Scientists suspect an outbreak of the Zika virus is behind a surge in a rare birth defect in Brazil. But how are they going to prove it?
Authorities in the South American country were quick to make the link last fall. The health minister last week said he was “absolutely sure” that the mosquito-borne virus is a cause.
But others aren't so certain. While the evidence has been mounting, so far it is circumstantial.
“The simple presence of the virus doesn't mean it caused the birth defect. It means there's a probability,” said Dr. Arnold Monto, a University of Michigan epidemiologist.
The investigation is still in its early stages. It began after Brazilian doctors noticed an increase last fall in babies with a birth defect called microcephaly, which has a number of causes. The cases closely followed the country's first outbreak of the tropical virus Zika, which was thought to cause no more than a mild illness that clears up in a week.
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