In the current outbreak, the rough estimate of cases in Brazil is 500,000 to 1.5 million, although it could be higher because many people who are infected show no symptoms.
The current list of countries and territories with reports of ongoing transmission in the Americas is as follows:
Barbados, Bolivia, Brazil, Colombia, Costa Rica, Curacao, Dominican Republic, Ecuador, El Salvador, French Guiana, Guadeloupe, Guatemala, Guyana, Haiti, Honduras, Jamaica, Martinique, Mexico, Nicaragua, Panama, Paraguay, Puerto Rico, St. Martin, Suriname, U.S. Virgin Islands and Venezuela.
Also on the list are American Samoa, Samoa and Tonga in the Pacific and Cape Verde off the west coast of Africa.
An imported case refers to an individual who contracted Zika in one country, then traveled to another country and was diagnosed with the virus there. In 2015 and so far this year, more than a dozen such cases have been reported in the U.S.
Vasilakis cites four or five cases in Florida, in individuals returning mainly from Venezuela and Colombia. There were several cases in Texas of people traveling from Latin America as well as a case where a person who contracted Zika outside the U.S. transmitted it to another person through sexual contact. And there was "the famous case in Hawaii," Vasilakis says, of a woman who was in Brazil while pregnant. Her baby was born with microcephaly, the birth defect that has been linked to Zika.
On Jan. 19, 2016, the first imported case of Zika virus was identified in Taiwan in a man from Thailand whose fever was detected upon arrival in Taiwan on Jan. 10 and who was subsequently tested. He likely caught the virus from a mosquito in Thailand, where there have been cases in the past. Spain has also confirmed that a pregnant woman, traveling from Colombia, has Zika.
But there has not been ongoing transmission in these countries (with the exception of the U.S. territories of Puerto Rico and the U.S. Virgin Islands).