two people may have contracted the virus from transfusions, but this has not been confirmed by national authorities, the World Health Organization or other agencies.

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Meanwhile, health officials in a growing number of countries are taking precautions to prevent contamination of the blood supply by urging potential donors to delay giving blood for about a month if they have been traveling in Zika-affected regions.

What is Zika?

A summary of the history of the virus from our Health section:

The virus was discovered in 1947 in a feverish rhesus monkey living in the Zika Forest of Uganda, but until 2007 scientists knew of only 14 human cases of the disease. That year it arrived on the travel-brochure-perfect Yap Island in the southwestern Pacific Ocean. Within a few months, nearly three-quarters of theisland’s 11,000 or so residents older than 3 had been infected. At first, those sick with Zika developed fever, joint pains and eye inflammation; then a red, bumplike rash erupted, sometimes followed by painful swelling of hands and feet. Some people vomited. Others were sensitive to light. But the symptoms usually resolved a couple of days later, and no one died.

In 2013, Zika popped up again, this time in Tahiti and other parts of French Polynesia. An estimated 28,000 people (about 11 percent of the population of those islands) felt sick enough with the virus to seek medical care. By 2014 it was showing up in several other South Pacific spots: New Caledonia, east of Australia; the Cook Islands; and, early this year, Easter Island, which marked the