Researchers and public-health officials don’t know enough about Zika because the virus is new to the Western Hemisphere, and they readily acknowledge the gaps in their understanding. It’s part of a family of viruses, called flaviviruses, that infect mosquitos, ticks, and their ilk. Some have familiar names: the aforementioned West Nile, dengue, yellow fever, and chikungunya. The Zika virus is transmitted by Aedes mosquitoes, which are found in roughly 30 states, including all of the American South. (The New York Times has a handy explainer on the virus and its history here.) Researchers at federal agencies are ramping up their investigations into the virus now, following a directive from President Obama. As it stands, there aren’t any diagnostic tests available commercially, nor are there vaccines or antiviral drugs available. Anthony Fauci, director of the National Institute for Allergy and Infectious Diseases, told reporters during a press call last week that a vaccine “probably” won’t be available “in the next few years.” Researchers in the Americas didn’t have any real motivation to develop these tools until recently, after an outbreak began in Brazil last year, infecting an estimated 1 million people, and then spread to 20-odd other countries, Puerto Rico, and the U.S. Virgin Islands.
The continental United States has seen cases in roughly a dozen states and Washington, D.C., but there’s a “big difference” between those cases and those seen in the Latin American outbreaks, Fauci said. The difference is that the U.S. cases are all associated with people who have traveled to affected regions; the United States hasn’t seen any locally transmitted cases, when “a mosquito bites a person infected with Zika and that mosquito passes that infection on to another person through a mosquito bite,” described Anne Schuchat, the CDC’s principal deputy director, on the same call.
That’s not to say local transmission won’t happen. But officials are saying—based on their encounters with other, similar viruses spread by mosquitoes—that it would be limited, as the United States is typically well-suited to containing mosquito-spread viruses. Common use of air conditioning and window screens help, and the United States doesn’t have the same kind of super-dense urban areas that have facilitated transmission in Latin America. For your average American not planning to travel to affected countries, Schuchat said, this shouldn’t be a worry. That said, a recent report in The Washington Post questions how limited the spread could be:
The South is seen as especially vulnerable because of its warm, humid climate and pockets of poverty where more people live without air conditioning or proper window screens. Plus, the region is already home to mosquitoes that can transmit the virus.
Some models estimate as many as 200 million people live in areas that might be conducive to the spread of Zika during summer months—including the East and West coasts and much of the Midwest. That makes for a huge target as researchers scramble to determine how the virus manifests itself in the human body, who is particularly at risk, and why.
The World Health Organization, which held an emergency meeting Monday on the virus, released preliminary estimates last week, based on the previous spread of dengue in Brazil, that 3 to 4 million people could be affected in the Western Hemisphere. Margaret Chan, the WHO’s director-general, said Monday that her organization can’t wait to move on a global response: “Can you imagine if we do not do all this work now and wait until all these scientific evidence to come out? People will say, Why didn’t you take action?”