The World Health Organization has announced that the explosive spread of the Zika virus in the Americas is an "extraordinary event" that merits being declared an international emergency.
The agency convened an emergency meeting of independent experts on Monday to assess the outbreak after noting a suspicious link between Zika's arrival in Brazil last year and a surge in the number of babies born with abnormally small heads.
Although WHO Director-General Dr. Margaret Chan said there was no definitive proof that the Zika virus, spread by mosquitoes, is responsible for the birth defects, she acknowledged on Thursday that "the level of alarm is extremely high."
The last such public health emergency was declared for the devastating 2014 Ebola outbreak in West Africa, which killed more than 11,000 people.
WHO estimates there could be up to 4 million cases of Zika in the Americas in the next year.
Who is at risk for Zika infection?
Most people in the contiguous United States are unlikely to ever come into contact with the Zika virus, but two groups need particular attention. First, people living in the Commonwealth of Puerto Rico, a U.S. territory, the U.S. Virgin Islands, Caribbean or Pacific territories, and Central and South America are likely to see an increasing spread of Zika. In these areas, women who are pregnant need to protect themselves from mosquito bites by using repellants, permethrin-coated clothing, long sleeves and pants, and by staying indoors (ideally in places with air conditioning) as much as is practical. We advise pregnant women to postpone travel to areas where Zika is spreading.
The spread of the virus through blood transfusion and sexual contact have been reported in isolated cases. However, for most of the nonpregnant population, there is no reason to think Zika presents a particular risk.
Will we see Zika in the U.S.?
We have already seen the Zika virus in travelers returning from places where Zika is spreading, including, sadly, one woman in Hawaii who delivered an infant with microcephaly after being infected with the virus in Brazil last year. We will certainly see more travelers returning to the United States with Zika after being infected in parts of the world where the virus is spreading. But the big question many people have is whether Zika will spread widely within the United States.
Science doesn't have a crystal ball, but the CDC has great laboratories and the world's best disease detectives. For a disease such as Zika to spread widely, two things are necessary. The first is the specific mosquito species that spreads the virus. The second is the conditions in communities; places that are crowded and don't have air conditioning enable viruses such as Zika to spread.
So we do expect, unfortunately, that Puerto Rico and the U.S. Virgin Islands could have many infections with the Zika virus, and we will certainly see U.S. travelers returning with Zika infections, just as we saw travelers returning with dengue and chikungunya infections. We could see isolated cases and small clusters of infections in other parts of the country where the mosquito is present. But from the information we know now, widespread transmission in the contiguous United States appears to be unlikely.
What is the government doing?
Since the first large Zika outbreak ever recognized, in 2007, the CDC has had boots on the ground responding. Our laboratories have developed a test that can confirm Zika in the first week of illness or in a sample from an affected child. Diagnosing prior infection with Zika is much more challenging, and CDC scientists as well as private companies are working to develop tests that can do this accurately. This is a priority, and we are working to do in weeks what would usually take months or years.
We are supporting laboratories in Puerto Rico and around the United States to provide testing, and we are using cutting-edge genomic methods in this effort. We are also working with Puerto Rico and other places at risk around the country to improve mosquito control efforts before we head into warmer weather when mosquitoes become a bigger problem. The CDC also provides support and guidance for health care providers and the public. You'll know of any new developments as soon as we do.
Across the Department of Health and Human Services, there is also important work related to Zika, particularly to speed the development of tests, treatments and vaccines.
Prevention will be key. Mosquito control is hard. States and cities that invest in mosquito control can track and fix many places where mosquitoes can breed to drive down mosquito populations. But this takes hard, meticulous work -- and money. We must maximize the use of today's tools to reduce the mosquitoes that can spread Zika and other diseases. We must also advance innovative mosquito control tools of tomorrow, such as promising new products that may be safer and more effective than today's methods.
There is no way to predict when or where health threats will emerge, but the plain fact is that we will continue to see new infectious disease threats such as Zika. The CDC's laser focus is protecting the health, safety and security of Americans; learning more about Zika and fighting it is a top priority.