How Worried Should You Be About Zika, Really?

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Photo: Joao Paulo Burini

You’ve no doubt read the headlines and seen the pictures: Since late October, more than 1,500 babies have been born in Brazil with a devastating birth defect caused by the mosquito-borne Zika virus, and another 3,000 possible cases of Zika-linked microcephaly have yet to be confirmed. While the outbreak has, thus far, hit Central and South America, experts are predicting that up to a quarter of people in Puerto Rico will be infected with the virus by the end of the year.

There have been a few hundred Zika cases in the United States, but they were all picked up elsewhere or passed on through sexual contact. We don’t have local transmission — yet. For that to happen, a mosquito would need to bite an infected person while there’s high levels of the virus in their blood, and then bite another person.

News sites have been warning you that Zika is coming and the Obama administration has sought more than a billion dollars to fight its spread. Now that summer is officially here: How worried should you be about it?

What is Zika exactly?

Zika is not a new disease, it’s just that when it reached Brazil in 2015, it infected as many as 1.5 million people, enough for even relatively uncommon side effects to become visible. Most people never develop symptoms, but the 20 percent who do experience a rash, fever, and joint pain. It usually lasts for about a week, then goes away on its own, or with some acetaminophen and rest.

People are understandably more concerned about the reports of microcephaly and an immune condition called Guillain-Barré syndrome that can lead to weakness of the arms and legs. But Guillain-Barré is relatively rare and usually temporary. Out of 756 travel-associated cases in the United States thus far, only three people have developed it.

There’s no vaccine or cure, but U.S. regulators just gave the makers of a possible vaccine the go-ahead to start human trials. The researchers hope to report their findings of the 40-person study later this year.

Zika is spread by the same mosquitoes that carry other scary-sounding viruses like dengue, yellow fever, and chikungunya, says Shannan Rossi, PhD, a virologist and research scientist at the University of Texas Medical Branch in Galveston, Texas. That bug is called Aedes aegypti, or the yellow-fever mosquito, and it does live in the southeastern United States, especially Florida and Texas, says Rossi, who specializes in the viruses transmitted by mosquitos. All the bug needs to start the process is a drink from an infected tourist or an American returning home.

So, is Zika coming to the U.S.? And how bad could it be?

For her part, Rossi isn’t convinced that it will. It’s certainly possible, but previous outbreaks of other mosquito-borne viruses offer some insight, plus there are structural differences to consider.

In Central and South America, she says, there are huge mosquito populations, and people’s homes aren’t necessarily insulated from the bugs. “If you go down to Brazil, for example, they don’t have screens on their windows, very few places have air conditioning, and they’re in an environment where the mosquitoes have contact with them almost all the time.”

“In previous outbreaks like the one that you saw for chikungunya and dengue, that was really a huge factor in prohibiting the virus from establishing itself in the U.S.” She also points to the fact that you’ll see cases of dengue on the Mexico side of the Rio Grande, but not on the Texas side.

For these reasons, she’s cautious about foretelling impending doom. “I wouldn’t necessarily say that it’s going to come with certainty. Absolutely, it has the possibility to and I don’t want to discount that it might happen, but I don’t think the question we should be asking necessarily is ‘when.’ But if we are going to see it, we’ll see some cases soon.”

Although, a little more than six weeks ago, one expert told NBC News that the risk of Zika circulating here would be peaking in the next few weeks, and yet here we are.

“I’m actually surprised we haven’t seen a case yet, but a lot of people are expecting at least a few cases of local transmission,” says Jeanne Sheffield, MD, an expert in pregnancy and infectious disease and the director of Maternal-Fetal Medicine at the Johns Hopkins Hospital.

Dr. Sheffield says she believes there will be limited, local transmission. “People are comfortable in saying that we don’t expect the outbreak to be, say, what we’re seeing in Puerto Rico right now, or Brazil, or Colombia.”

And the risks of contracting Zika — and experiencing possible ill effects — will vary depending on where you live and what stage of life you’re in, Rossi says.

Okay, how screwed am I?

Back to the bugs. Some maps show that yellow-fever mosquitos exist in almost half the country, which is unsettling. But there’s a second mosquito that has the potential to transmit Zika, at least in a lab setting, Rossi says. The Asian Tiger mosquito (or Aedes albopictus) has been spotted in even more places in the United States than the yellow-fever mosquito, but it remains to be seen if it carries the virus in the real world.

Either way, these maps have the tendency to make people terrified. “When you look at maps from what major news outlets have published, or from what the CDC published, it can be really alarming if you see your entire state glowing … But that doesn’t necessarily mean that your backyard has that mosquito. Those maps can be kind of misleading and really conjure up fear.” The CDC at least includes some words of caution:

These maps include areas where mosquitoes are or have been previously found. Maps are not meant to represent risk for spread of disease. Aedes aegypti mosquitoes are more likely to spread viruses like Zika, dengue, chikungunya and other viruses than other types of mosquitoes such as Aedes albopictus mosquitoes.

But even if the Asian Tiger can transmit Zika, Rossi thinks sexual transmission will probably end up affecting Americans more than mosquito bites, again, thanks to our screened-in windows and air conditioning. (Pro tip: Both kinds look different from the so-called southern-house mosquito that’s known for transmitting West Nile virus; namely, they have white stripes on their legs.)

Experts believe that Gulf Coast states like Florida, Texas, and Louisiana have relatively higher risks than other states, and travel hubs could see more Zika activity, too.

“If I live in Montana, Zika’s not an issue. You just don’t have the mosquitoes, you don’t have the influx of traffic coming from endemic areas,” Rossi says. “The risk is a little bit higher in some places like New York City where you have traveler-associated cases, but you don’t necessarily have the high prevalence of the mosquito population to sustain it.”

And if, say, you’re an older man not planning on having kids any time soon, your concerns are different from younger people thinking about kids. “If you’re pregnant or you’re seeking to become pregnant quickly, you need to take more precautions than if you’re really young or you just don’t plan on starting a family anytime soon,” she says.

“If you’re really, really wanting to plan a family and you’re living in Minnesota where the mosquitoes aren’t, you shouldn’t delay your family. But at the same point, if you’re pregnant, don’t go to Rio.”

Yeah, I’m pregnant. What’s the risk of birth defects from Zika?

Not all pregnant women infected with Zika will pass the virus to their fetus, or have babies with microcephaly. Some will miscarry, some will have totally healthy newborns. It’s believed to be most risky when the mother is infected in the first trimester, but there have also been reports of miscarriages and birth defects when the mother was infected relatively late in pregnancy.

But, at this point, experts still don’t know the prevalence of birth defects in Zika-infected pregnant women. There are multiple studies that offer some ideas but, unhelpfully, they say different things.

A study published in March that looked at an outbreak in French Polynesia between 2013 and 2015 found that one percent of women infected in the first trimester gave birth to babies with microcephaly. Another paper from May said the risk was “up to” 13 percent. One of the leaders of the Centers for Disease Control and Prevention’s birth-defects team says the estimated risk is between one and 15 percent.

A small study involving women in Rio de Janeiro found that, of the 42 women who tested positive for Zika and had fetal ultrasounds, abnormal results were seen in 12 cases, which works out to 29 percent. This sounds terrifyingly high, but there were another 30 infected women not included in that calculation: Two miscarried and 28 declined the scans, so we don’t know the full picture.

Why are these numbers all over the place? Partially because so few people develop symptoms, Dr. Sheffield says. “We still don’t know how many pregnant women actually have been infected with Zika,” she says. “We have a number of how many pregnant women have been tested, but there are probably a ton of pregnant women out there who were infected that were completely asymptomatic.”

“Trying to figure out a true percentage of transmission is incredibly difficult because we just don’t know what our denominator is in the first place,” says Dr. Sheffield, who worked with the CDC, the American College of Obstetricians and Gynecologists, and the Society for Maternal-Fetal Medicine to publish guidance for health-care providers on treating pregnant women with Zika.

She says it would be “almost impossible” to test every pregnant woman in the United States, where there are more than 4 million births per year, and even more pregnancies. Currently, doctors here are only testing women who may have been exposed.

Jamaica’s health department recently said it would start testing every pregnant woman for Zika, symptoms or no symptoms. (The island nation has between 35,000 and 45,000 births per year.) Dr. Sheffield says that information would be a great step forward, but we won’t have it anytime soon.

Meanwhile, Sheffield and other doctors are simply being forthcoming about the knowledge gap. “When we’re counseling pregnant women [with exposure risk], we are literally telling them, ‘We still don’t know what the transmission risks are, whether you’re symptomatic or asymptomatic, if you are infected we will be following you the same.’” Currently, the protocol includes serial ultrasounds.

What should I do to protect myself?

If you’re pregnant, the CDC recommends avoiding travel to areas with Zika transmission (here’s a list of countries) and taking steps to prevent mosquito bites. That includes clearing standing water around your home, using screens on windows and doors, staying in air conditioning, wearing long sleeves and long pants when outside, using EPA-registered insect repellent and, for extra protection, treating clothes with permethrin. The CDC also advises that women and men avoid bites if they’re trying to get pregnant.

And, yes, Dr. Sheffield says DEET is safe for women who are pregnant or breastfeeding when used as directed. The CDC and ACOG agree. Even the chemophobe Environmental Working Group recommends pregnant women use repellent with 20 to 30 percent DEET for Zika protection.

You don’t have to use DEET since the active ingredients picaridin, IR3535, oil of lemon eucalyptus, or para-menthane-diol work well, too. Bottom line: This is not a time to try some natural balm from your weird neighbor or a new product being marketed specifically for Zika. “Please use what is known to work,” she says. And take note: Repellent should be applied after sunscreen and only on exposed skin, not under clothing.

Zika can also be transmitted sexually and, thus far, it’s only been passed from men to their partners, not from women. (Eleven of the country’s 756 cases were sexually transmitted.) If you’re pregnant and your male partner traveled to an area with Zika, the CDC recommends using condoms until the baby arrives for any kind of sex, including oral. The alternative is to remain celibate.

What if I’m not ready to have kids, or not sure, or too scared?

Dr. Sheffield says lots of women ask her if they just shouldn’t get pregnant right now, and she reminds them that this isn’t Brazil. “I keep telling them ‘Look, I’m not going to tell you not to get pregnant. For one thing, we don’t have it in the United States yet and, if we do, I do expect that it will be limited compared to what we’re seeing elsewhere.’ I’m telling people that if they do get pregnant, or if they’re considering pregnancy, they should absolutely use preventive measures.”

If people want to get pregnant and they’ve been exposed to Zika, both the CDC and the World Health Organization recommend waiting eight weeks before trying. If a man develops symptoms or tests positive, couples should wait six months.

And if you happen to get the virus now, she says there’s no need to worry about it affecting pregnancies months or years later. “The CDC has come out and said pretty comfortably that if you are Zika-infected and you clear the virus, there are no long-term consequences,” Dr. Sheffield says. Their reason for saying so isn’t because they know for certain that future pregnancies won’t be affected, but other viruses in the same family, like dengue and chikungunya, aren’t chronic, and they can look to the previous Zika outbreak in French Polynesia.

And because this is the United States, not a country in Central or South America, women here have much better access to birth control and long-acting contraceptives like IUDs should they choose to keep their uterus a baby-free zone. If you’re not trying to get pregnant soon, there’s no reason to freak out, though Dr. Sheffield recognizes that worrying is only natural.

Women could worry about the possibility of a viral outbreak that could maybe, possibly affect their not-yet-conceived children, but Rossi says she wouldn’t lose sleep over it.

“There are so many other risky things that we do. You’re probably way more likely to get hurt trying to cross a street in Manhattan than you are from Zika,” she says. “Every day we make risk assessments based on what we know around us. We shouldn’t be paralyzed by fear moving forward, but it’s good to know what’s out there, so that you can take the appropriate precaution. So you can say, ‘Okay, I wore my bug spray; I’ll reapply it in a couple hours after I sweat if off, and move on with my life.’”

My Month With Zika