What Threat Does Zika Pose to the United States?

Fearful of the effects of the Zika virus on unborn children, El Salvador has urged women to stop having kids altogether. Colombia and Ecuador have dispensed similar warnings amid an outbreak of a virus that has resulted in thousands of children in Latin America being born with a condition known as microcephaly — which leaves them with abnormally small brains.

So when the World Health Organization said on Monday that the Zika virus, which is transmitted by a certain mosquito species, was likely to spread to the entire Americas, the reaction among expectant mothers was one of panic. There is no medicine or vaccine to prevent Zika infection — besides not getting bit by an infected mosquito — and the link between the virus and birth defects remains poorly understood. The U.S. Centers for Disease Control issued treatment guidelines for expectant mothers on Tuesday, and the head of the National Institutes of Health called for an aggressive effort to study the disease more closely. CDC did not respond to a request for comment Tuesday.

The awful birth defects associated with the virus and the lack of preventative treatments have resulted in authorities taking drastic measures in several Latin American countries. Medical historians say El Salvador’s recommendation that women not get pregnant is historically unprecedented and raises the possibility that this Zika outbreak may become a generationally defining event for parts of Latin America. Brazil will deploy 220,000 troops to spread awareness about Zika next month.

But what risk does the virus actually pose to the United States? Scientists who have studied the disease say that it is unlikely that the United States will see a mass outbreak like the one in Brazil, which has been hardest hit by the virus, linked to more than 3,800 cases of microcephaly.

The virus has already turned up in the United States, but there have so far been no confirmed cases of transmission inside the country, with cases limited to individuals who had traveled in the region and returned with Zika. Authorities in Arkansas said Tuesday that a person who had traveled in Central America had tested positive for Zika. A child born in Hawaii earlier this month with microcephaly tested positive for Zika. Her mother had lived in Brazil early in her pregnancy.

According to the World Health Organization, at least 22 countries and territories in Central and South America and the Caribbean have seen cases of the virus, including the American territories of the U.S. Virgin Islands and Puerto Rico, which has 19 cases of Zika.

In order for the Zika virus to spread, it requires a favorable climate and the help of a certain type of mosquito — the virus cannot spread through human-to-human contact. That combination of right temperature and correct mosquito is found in parts of southern Florida, the Gulf Coast, and pockets of Southern California, said Kamran Khan, an infectious disease physician and scientist at St. Michael’s Hospital in Toronto.

Khan said he believes the United States may see sporadic outbreaks but nothing on the scale of the more widespread outbreaks in Latin America.

But that doesn’t mean that the disease won’t establish itself in the United States. According to research carried out by Khan and a team of scientists and published in the medical journal Lancet, some 2.7 million people left Brazilian airports in areas affected by Zika and traveled to the United States from September 2014 to August 2015. Khan’s team estimates that 200 million Americans live in areas that could see Zika spread through mosquitos during the warmer months.

On Tuesday, President Obama met with his health and national security advisers to discuss steps being taken to prevent Zika’s spread to the United States, according to a White House readout of the meeting.

For the disease to establish itself in the United States, a person infected with the virus would have to arrive in the United States and be bit by a mosquito that would pick up the virus. That mosquito would then need to bite another person in order for the disease to be passed on.

Khan pointed out that U.S. authorities would likely be far more effective in carrying out mosquito extermination efforts than their Latin American counterparts, and would likely be better able to stem the disease’s spread. The widespread use of air conditioning in the United States would likely further mitigate Zika’s spread because mosquitoes capable of carrying Zika do not like the cold. Robust public health systems in the United States would likely be better equipped to counter a widespread outbreak, Khan said.

For now, doctors know little about the connection between Zika and microcephaly, but that hasn’t stopped intense fears among expecting mothers that they could be affected. Isaac Bogoch, a doctor at the University of Toronto who worked on Khan’s study, says he has been inundated with phone calls from expectant mothers who have traveled in Latin America in recent days, as news of the virus has spread. “If it wasn’t for the potential association with birth defects, this virus wouldn’t be given nearly as much attention,” Bogoch said.

Those infected with the virus will exhibit only mild symptoms — a fever, perhaps a rash, and joint pain. For most, it will pass in several days. The possibility that the virus may be linked to awful birth defects has led many expectant mothers to put off traveling to Latin America, Bogoch said. That precaution may be reasonable for expectant mothers he said, but others shouldn’t need to cancel travel plans to affected regions, as long as they take precautions to reduce their chances of being bit by a mosquito.

Studies have found links between Zika and microcephaly, but no scientists have identified a causal relationship between the two. In Brazil, doctors have observed a surge in microcephaly cases in areas hard hit by Zika. Doctors have found the virus in the amniotic fluid of mothers whose children were affected by microcephaly. Tissue samples from fetuses that were not carried to completion and exhibited signs of microcephaly have also revealed the presence of Zika.

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