The mosquito-borne Zika virus is spreading so quickly through the Western Hemisphere that it is soon expected to reach nearly every country in the Americas. The virus has already affected more than a million people in Brazil, and it's likely to reach the continental United States this year.
Health officials are increasingly alarmed at this prospect. Most of the time, Zika causes no symptoms at all — or at worst, a rash, fever, and achy body. But there's mounting evidence that Zika can harm fetuses. A worrisome number of pregnant women who contracted Zika in Brazil last year have given birth to babies with microcephaly, a condition that stops babies' heads from reaching full size.
The link between Zika and birth defects still isn't well understood (nor is the virus's association with Guillain-Barré, a neurological syndrome that can lead to paralysis). Until very recently, Zika had been a relatively rare disease and a remote threat to humans. In the absence of clarity, public health agencies around the world have been scrambling to respond, with some officials warning women in Latin America to avoid pregnancy if they live in places with Zika. In the US, the Centers for Disease Control and Prevention (CDC) issued an unprecedented travel advisory, warning pregnant women and women of childbearing age to avoid countries where Zika is currently circulating.
Right now we have no treatment or vaccine to stop the virus, and those may take years to develop. So what can we do to control Zika and avoid more outbreaks in the meantime? According to experts who study the disease, here are some of the key steps:
1) First, we need to get serious about tracking Zika
The CDC has said that future Zika outbreaks in the United States are likely to be caused by infected travelers returning home with the virus from elsewhere. But until now, there's been no way of knowing for sure who those infected people might be.
That's because Zika was only just officially labeled a "nationally notifiable disease" — a designation the CDC gives to serious diseases (like malaria or Ebola). This step should allow better tracking and surveillance in the future, helping public health officials coordinate their responses and have a more precise sense of where people with Zika are living and where local outbreaks are likely to happen.
This is only a start. Health professionals need to consider Zika in patients who have traveled in South and Central America and the Caribbean, and have symptoms of the disease. They need to report suspected cases to their local public health agencies. Doing this won't be easy. There are no commercially available tests for Zika, so all testing right now is done through state and federal labs. And the virus can look very similar to other diseases that are currently circulating in the south.
"Based on the typical clinical features, the differential diagnosis for Zika virus infection is broad," the CDC warns. "In addition to dengue, other considerations include leptospirosis, malaria, rickettsia, group A streptococcus, rubella, measles, and parvovirus, enterovirus, adenovirus, and alphavirus infections (e.g., Chikungunya, Mayaro, Ross River, Barmah Forest, O’nyong-nyong, and Sindbis viruses)."
For now, the CDC has issued information on diagnosis and testing for health providers, as well as interim guidance on looking for congenital Zika virus infection and how to care for pregnant women in an outbreak.
2) Next, educate the public about Zika and mosquitoes
In Brazil — which has seen more than a million cases of Zika and a worrisome rise in birth defects — the government has resorted to deploying troops to educate people about mosquitoes and how to reduce Zika exposure. Other countries should also start thinking about education.
Zika is carried by a specific type of mosquito called Aedes aegypti, which spreads the disease through bites. This mosquito, with distinctive white markings on its body, is remarkably effective at carrying viruses — it's also the primary vector of the yellow fever, dengue, and chikungunya viruses. There's some experimental evidence suggesting the Asian tiger mosquito (Aedes albopictus) can transmit the virus, too.
These Aedes mosquitoes can be found throughout America, and their range seems to be expanding in recent years:
People living in these areas should learn how to reduce their risk of bites.
The Aedes has adapted to breed and rest in small pools of water and moist environments around people's homes. (You can see examples of the mosquito's main aquatic habitats here, ranging from rain-filled cavities in trees to outdoor pots and animal drinking pans.)
"If you have a Styrofoam cup in your backyard that gets flooded when it rains, it won't have any predators in it," says Janet McAllister, a researcher in the division of vector-borne diseases at CDC. "So the Aedes aegypti will prefer that instead of a big, open pool that dragonflies might lay eggs in."
"Just generally keeping your yard clean and in shape, getting rid of debris or things stored outside that can hold water, or adjusting them so that they no longer hold water," McAllister said. "It's also important to maintain the vegetation in your yard — to keep the grass mowed and bushes trimmed, with good air flow." All these measures will make the space around your home less hospitable to mosquitoes.
Inside the home, the CDC recommends making sure you have screens on windows and doors that aren't punctured in any way. Wearing protective clothing, using insect repellents, and keeping your house cool with air conditioning also helps.
3) We need to start mosquito control programs now
Ultimately, however, there's only so much that individuals can do; organized eradication campaigns may also prove necessary.
In theory, we should be able to reduce the Aedes mosquito's range. In the mid-20th century, an eradication program had wiped out the species from much of the Western Hemisphere. The problem is that those programs weren't maintained, and so the mosquitoes have gained a foothold all over the Americas again.
Such mosquito control programs would involve a variety of strategies. They would entail launching public education campaigns about mosquitoes (as described above), treating certain bodies of water with larvicide, organizing neighborhood campaigns to clean up people's yards and work sites, and instituting tire pickup programs (old tires are a popular breeding place).
"The best way to do this is integrated pest management where you use multiple tactics and tools to address the control of mosquitoes," said McAllister.
"Effective health measures include fumigation to kill adult mosquitoes and elimination of mosquito breeding sites," adds Dr. Jose Luis San Martin, an adviser who works with the Pan American Health Organization's neglected, tropical, and vector-borne diseases unit.
Targeting communities with poorer sanitation may prove to be critical, added Martin. "This is a mosquito that has very successfully adapted to domestic life, and our countries [in Latin America] have great difficulty, especially with belts of poverty around cities, with poor housing, lack of access to clean water — which leads families to store water in tanks, which, if not properly covered or treated, then become breeding grounds."
Another, more controversial method would be to use genetically modified Aedes aegypti mosquitoes that can essentially help sterilize the population.
Still, if we want to minimize Zika's risks, these measures need to be implemented soon. Currently, about 22.7 million people live in humid areas where mosquitoes can be found. By the time the summer rolls around, as many as 200 million Americans could be within range of mosquitoes that can carry the Zika virus.
"They should be planning for that now, because it’s going to happen quickly and they are going to need to respond quickly," said McAllister.
What's more, we may want to pay attention to other types of mosquitoes that might also carry Zika. The Aedes albopictus has a much larger range in the United States, reaching at least 32 states. Again, experimental evidence suggests it can transmit the virus, and if that happens, we should be ready.
4) Pregnant women should avoid traveling to places where the virus is circulating
No one's yet developed a vaccine to prevent Zika, so simply avoiding mosquitoes in countries where the virus has been circulating is the best defense.
Because of the potential for birth defects, the CDC has warned pregnant American women and women of childbearing ages who may become pregnant to stay out of places where the virus is currently circulating.
Right now, that list includes more than 20 countries: Barbados, Bolivia, Brazil, Colombia, Dominican Republic, Ecuador, El Salvador, French Guiana, Guadeloupe, Guatemala, Guyana, Haiti, Honduras, Martinique, Mexico, Panama, Paraguay, Puerto Rico, Saint Martin, Suriname, Venezuela, and the US Virgin Islands. Officials warn that more countries will be added soon.
In addition, the CDC recommends that everyone traveling to areas with Zika virus take precautions to protect themselves — wearing mosquito repellent, using screens to keep mosquitoes outside, wearing pants and long-sleeved shirts, and making sure there's no standing water inside or outside the home.
5) We need to step up research efforts on Zika — and work on a vaccine
There are still many questions around Zika. Researchers don't know exactly how it affects fetuses or how common birth defects are. They don't know the full range of symptoms the virus can cause or understand its links with neurological conditions. They don't even fully understand all the ways it can spread. (There's some evidence that Zika may be transmitted through sexual intercourse, though the studies to date have been tiny.)
With such high stakes, however, researchers are calling to speed up Zika research and development. "I’ve made it clear that we want to put a full-court press," said Dr. Anthony Fauci, head of the National Institute of Allergy and Infectious Diseases, in a Time magazine interview. The agency is currently researching vaccine candidates and how to make testing more widely available.
Beyond the clinical questions around Zika, we also need to understand what public health interventions and mosquito-control efforts are most effective and how to get those launched in places that are currently experiencing or are likely to see Zika outbreaks. Doing so sooner rather than later could help prevent a tragedy.