If and when a mosquito infects a person in the continental United States or Hawaii with the Zika virus, US health officials will deploy a strike team to further limit the virus’s spread, with the ultimate goal of protecting pregnant women.
The rapid-response teams — which will help local officials with surveillance, mosquito control, and lab testing — were highlighted in a draft plan released Tuesday by the Centers for Disease Control and Prevention. The 58-page plan outlines how the agency will respond to even a single suspected case of local transmission, which experts say could occur for the first time this summer as mosquitoes grow more active and expand their habitats.
The CDC says it will update its plan if new information emerges about the virus’s possible spread.
These CDC Emergency Response Teams will offer support to local agencies, and once in the field will help track the source of infection. They will also reach out to pregnant women in the area to help them avoid mosquito bites and secure the local blood supply in cooperation with the Food and Drug Administration.
States in the south and southwest, as well as Hawaii, are already on the lookout for locally acquired cases, because they are home to the largest populations of the mosquito species, Aedes aegypti, thought to be responsible for the wave of cases that has swept through Latin American and Caribbean countries, as well as Puerto Rico. The large majority of the roughly 700 cases so far in the 50 states and Washington, D.C. are in people who contracted the virus while traveling. The virus can be sexually transmitted as well.
The Zika virus rarely triggers anything more than a mild illness. But it can cause a range of severe birth defects when it infects pregnant women and their fetuses, including a condition called microcephaly, which is characterized by abnormally small heads and underdeveloped brains. More than 200 pregnant women in the 50 states and Washington have had some evidence of a Zika infection, and officials have been saying for months their top priority is to prevent pregnant women from being infected.
The most likely scenario for local transmission is that a mosquito bites a person who contracted the virus while traveling and has returned home. If the mosquito in turn becomes infectious, it can then spread the virus to the person’s relatives or neighbors when it bites them.
But most experts expect only limited transmission and small clusters of cases in the continental United States and Hawaii. Cities in the US are generally less dense than in the rest of the Americas, where infectious mosquitoes can easily bite several people without traveling far. Air conditioning and screened windows are also much more common, reducing residents’ exposure to mosquitoes.
Plus, the continental United States has only seen a handful of locally contracted cases of viruses like dengue and chikungunya, which are transmitted by the same mosquitoes and have spread widely in Central and South America. If those viruses have been limited here, the thinking goes, then it should be the same with Zika.
The mosquito control aspect is an important component of the CDC’s plan. Many cities and counties around the country do not have a dedicated vector control agency and depend on public works crews to target the insects. A surge in mosquito control efforts directed at the area immediately surrounding the site of local transmission could stall any wider spread because Aedes aegypti do not travel more than a few hundred yards in their lifetimes.
The response teams will “stand down” after 45 days if there is no wider transmission, the CDC draft plan says. The response will be more intensive depending on the number of people infected and if the chain of transmission isn’t cut quickly.
Experts will have to first rule out sexual transmission and wait for definitive lab tests before confirming a case of local transmission. Another challenge: many people with Zika do not show symptoms or seek medical care.
“It’s really going to depend on the provider community thinking about it early and asking the right questions and getting public health [officials] involved,” said Dr. Jeff Engel, the executive director of the Council of State and Territorial Epidemiologists.
Engel said the CDC’s plan was comprehensive and, given the situation, provided an outline for protecting pregnant women and controlling local transmission.
“Like with all new problems, you have to start somewhere,” he said. “I think the epidemiology community is fairly pleased with what the CDC has proposed — it makes a lot of sense.”
The fear of what the virus can do to fetuses has galvanized a response among agencies at all levels. The CDC has been talking with state and local agencies for months about how to prepare, encouraging them to bolster mosquito control programs and working with clinicians to be on the lookout for symptoms, which include fever and rashes.
States most at risk for the spread of Zika have also been working to limit its impact and have been calling on Congress to fund a Zika plan. Florida is investigating suspected cases even before lab results determine whether someone has Zika, Engel said. Last week, Florida Governor Rick Scott requested an additional 1,300 Zika antibody tests from the CDC.
Alabama, meanwhile, has upgraded its lab so it doesn’t have to outsource Zika testing to the CDC, said Jim McVay, the director of health promotion and chronic disease at the Alabama Department of Public Health.
States have also been enlisting the public to control mosquitoes by encouraging them to dump standing water that mosquitoes use to breed. McVay said Alabama distributed more than 240,000 educational coloring books to elementary school students about Zika in both English and Spanish.
“It has to be a local response, and even when the CDC sends someone in, you’re going to have to work with the local medical community and the local community,” McVay said. “It’s always going to come to what you’re doing locally.”