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An Aedes aegypti mosquito, the vector of Zika virus. Photograph by James Gathany, CDC.

For Fear of Zika, CDC Recommends Pregnant Women Not Travel

(This post has been updated with news of the first Zika birth defects case found in the United States.)

In an extraordinary statement likely to launch international controversy, the US Centers for Disease Control and Prevention recommended Friday evening that pregnant women not travel to 14 countries and territories—the commonwealth of Puerto Rico, and Brazil, Colombia, El Salvador, French Guiana, Guatemala, Haiti, Honduras, Martinique, Mexico, Panama, Paraguay, Suriname, and Venezuela—for fear of birth defects associated with infection by mosquito-borne Zika virus.

The recommendation comes in the form of a “Level 2 travel alert,” which in the agency’s lingo represents a warning to “practice enhanced precautions.” In the Zika announcement, the CDC says that pregnant women “should consider postponing travel,” adding, “pregnant women who must travel to one of these areas should talk to their doctor or other healthcare provider first and strictly follow steps to avoid mosquito bites.” Women planning to become pregnant, it says, “should consult with their healthcare provider before traveling to these areas.”

Zika virus has been exploding in South and Central America. In Brazil, where the virus arrived just seven months ago, there have been more than 1 million cases of infection, and more than 3,500 cases of a rare birth defect called microcephaly, babies born with smaller than normal skulls and brains.

The warning follows the CDC’s own analysis of samples from two stillborn children and two who died after birth who suffered microcephaly. The agency said:

“For the two full-term infants, tests showed that Zika virus was present in the brain. Genetic sequence analysis showed that the virus in the four cases was the same as the Zika virus strain currently circulating in Brazil.  All four mothers reported having experienced a fever and rash illness consistent with Zika virus disease during their pregnancies.”

The countries and territories named by the CDC Friday are jurisdictions where Zika virus transmission has been confirmed. (On Friday, one other country not mentioned in the CDC’s list, Guyana, also reported cases, according to Caribbean media.)

The warning not to travel—made, the CDC said, “out of an abundance of caution”— is likely to be controversial. It warns women away from the site of the Olympics, which take place in Rio de Janeiro in August, as well as from most of the beach and tourist economies of Central and South America. In what may be a first, it warns citizens of the United States from entering a part of the United States, the unincorporated territory of Puerto Rico.

Puerto Rico is part of the advisory because Zika infections have occurred there. Zika has also landed in Texas, via a local resident who was infected in Latin America and returned there, but has not been transmitted locally.

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How far the risk of imported Zika might be spread by local mosquitoes. Graphic from Bogoch et al., The Lancet.

But researchers from several countries said in The Lancet Thursdaysaid in The Lancet Thursdaysaid in The Lancet Thursday that infected travelers should also be considered a risk to their home countries, because virus levels in their blood could be high enough to pass Zika back to local mosquitoes when they return.

As a result, they said, some among the 9.9 million travelers who leave from Brazilian airports every year could bring the disease with them and establish it at their destinations. The US receives 2.7 million travelers yearly from Brazil; Italy, 419,000; France, 404,000; and China, 84,000.

The main mosquito species responsible for spreading Zika, Aedes aegypti, flourishes in the far Southern US, and a second species that may transmit the virus, Aedes albopictus, ranges as far north as New York. Thus, the researchers said, if Zika virus came to the United States, 22.7 million people — primarily in Southern California, South Texas and Florida — would be at risk of contracting the disease year-round, and possibly 60 million seasonally if both mosquito species were involved.

Update: Late Friday evening, the CDC also sent out a HAN, a Health Alert Network advisory to health care workers to help them recognize possible cases of Zika. It’s here.

Update 2: Also late Friday, the Hawaii State Department of Health announced that it has identified the first case of Zika-related birth defects in the US, in a baby born on Oahu to a woman who became pregnant while living in Brazil last summer.

“This case further emphasizes the importance of the CDC travel recommendations released today,” state epidemiologist Dr. Sarah Park said in the announcement. “An astute Hawaii physician recognized the possible role of Zika virus infection, immediately notified the Department of Health, and worked with us to confirm the suspected diagnosis.”

So far six Hawaii residents have been found infected with Zika, the announcement said, but all caught the disease outside the state. Hawaii has made Zika a reportable disease, which means physicians who recognize a case are obliged to inform the state department.

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