Ahh, Memorial Day! For generations of Americans, the holiday has marked the beginning of the season of sunscreen, barbecues and chlorine. It’s when you start putting sticky notes all over the guidebooks for that exotic trip abroad. And when you start tuning out at work and daydreaming about lying on a hammock with a thick paperback and a smoothie in hand. But this year, the long weekend also signals something a little more ominous. This is when you should start getting serious, if you haven’t already, about Zika.

U.S. health officials warn that mosquitoes carrying the virus could hit the mainland’s southern borders — starting with Florida and the Gulf Coast — in a few weeks, and as the list of affected countries continues to expand, so does the likelihood that one of those places will be on your itinerary. The latest additions include Argentina, Grenada, St. Barts and Peru.

Everything you ever wanted to know about the Zika virus and its spread across North and South America. (Daron Taylor, Claritza Jimenez/The Washington Post)

The World Health Organization and U.S. Centers for Disease Control and Prevention have confirmed the link between Zika and thousands of infants being born with abnormally small heads. A study published this month by researchers at the CDC and Harvard found that pregnant women who are infected with the virus in their first trimester may face a risk as high as 13 percent that their child will develop the condition, which is often accompanied by incomplete brain development. The WHO has also acknowledged that the virus appears to be connected to some cases of the autoimmune nervous disorder Guillain-Barré in adults and is investigating its possible role in a third neurological condition known as ADEM. ADEM, or acute disseminated encephalomyelitis, involves a brief but often very serious attack of inflammation on the brain and spinal cord.

There’s no consensus about what’s going on. Some scientists think that as the virus rapidly spreads to larger populations, we’re just starting to notice the more serious effects of Zika, which until recently was not thought to be particularly dangerous as most people are asymptomatic or only experience mild symptoms such as a rash and fever and fully recover. The other possibility is more frightening. It’s that the virus, which was discovered in 1947,  has evolved into a more virulent form — and may continue to evolve.

So as you race through the house trying to find those flip-flops and wide-brimmed hats, take a moment to look through the latest information about Zika and some advice from experts about precautions you should be taking.

Where can I find the current list of countries where Zika is active?

The list of countries with travel advisories can be found here on the CDC’s main site. U.S. health officials have been updating this page when there are changes, so check back often.

The Caribbean: Aruba; Barbados; Bonaire; Cuba; Curaçao; Dominica; Dominican Republic; Grenada; Guadeloupe; Haiti; Jamaica; Martinique; the Commonwealth of Puerto Rico, a U.S. territory; St. Barthelemy; St. Lucia; St. Martin; St. Vincent and the Grenadines; Saint Maarten; Trinidad and Tobago; and the U.S. Virgin Islands.

North/Central America: Belize, Costa Rica, El Salvador, Guatemala, Honduras, Nicaragua, Panama;
The Pacific Islands: American Samoa, Fiji, Kosrae (Federated States of Micronesia), Marshall Islands, Mexico, New Caledonia, Papua New Guinea, Samoa, Tonga.

South America: Argentina, Bolivia, Brazil, Colombia, Ecuador, French Guiana, Guyana, Paraguay, Peru, Suriname, Venezuela. 2016 Summer Olympics (Rio 2016)

Africa: Cape Verde

Who should not go to the countries on that list?

If you are pregnant, especially if your trip would take place in the first trimester. Health officials are also urging women who want to conceive soon or men who want to start a family in the next six months to reconsider their plans. While most of the cases of Zika have been from mosquito bites, there have been a handful of documented cases of Zika-infected men passing on the virus to their female partners.

My destination is on the CDC list, but I’m NOT pregnant. How should I weigh the risks?

In the vast majority of cases, Zika is not a danger. Most people infected don’t experience symptoms, and even those that do have very mild ones such as rash, fever, joint pain and red eyes that go away after a few days to a week. It has been linked to two neurological conditions in adults, but those are very rare. To date, the WHO and CDC have not gone as far as to issue a travel moratorium to those parts of the world. It would be impractical, for one, as the virus is spreading rapidly and in all probability, you might not have to travel anywhere to be exposed as the mosquitoes may show up in your own back yard if you live in the southern part of the United States.

The CDC says the best way to reduce your risk is to avoid bug bites by using repellent, covering your skin and choosing hotels with screens or air-conditioning, if possible.

Is it safe to take my young daughters? If they get Zika, could it cause problems for them if they get pregnant as adults?

Scientists think that once the infection has passed, it should not affect a woman’s ability to have children or risks of complications. That is, the virus does not seem to have a permanent effect on the female reproductive system. There is evidence Zika causes damage by passing into the baby’s brain in utero and somehow interferes with the organ’s formation at its most vulnerable time during the first trimester. But once the active virus is out of a woman’s body, and only antibodies remain as evidence that she even had an infection, her future children should not be in the same danger. This is also why doctors think that women who have given birth to a baby with microcephaly because of Zika are unlikely to be at any higher risk during subsequent pregnancies. In fact, the opposite may be true assuming that the virus can only infect a person once. If they are immune, their bodies could not host the active virus, so their babies would be safe.

What about the United States? What states/areas should I worry about?

There are two types of mosquitoes that carry the Zika virus, and scientists have created some models of where they tend to go. This is the best information we have about their projected trajectory in the next few months. If you're vacationing in the the northern part of the country, you probably don't have to worry very much. But if you're going south, you probably want to be slathering on the mosquito repellent. Notice that the range of the Aedes albopictus, the second type of mosquito carrier, goes significantly farther north than the Aedes aegypti species that everyone was talking about earlier in the outbreak. That means that even if you are in the Mid-Atlantic, parts of New England or even the southernmost parts of Maine and Minnesota, you may need to be cautious.

Which mosquito repellents really repel mosquitoes?

While the CDC and Department of Health and Human Services can’t recommend or endorse any specific brands, they suggest consumers look for products that are registered with the Environmental Protection Agency. "The effectiveness of insect repellents that are not registered with the EPA, including some natural repellents, is not known," they warn. Below are ingredients in products proven to be effective against mosquitos:

  • DEET — Look for repellents that contain at least 20 percent DEET, examples include Cutter Backwoods and Off! Deep Woods
  • Picaridin (also known as KBR 3023, Bayrepel and icaridin) — Examples include Cutter Advanced, Skin So Soft Bug Guard Plus and Autan
  • Oil of Lemon Eucalyptus (OLE) or para-menthane-diol (PMD) — Examples include Repel Lemon Eucalyptus
  • IR3535 — Products include Skin So Soft Bug Guard Plus Expedition and SkinSmart

The CDC also offered the following tips:

  • When using insect repellent, follow the instructions on the package and reapply as directed. In general, higher percentages of the active ingredient provide longer-lasting protection. However, this increase in protection time maximizes at about 50 percent DEET.
  • If you are also using sunscreen, apply it first, let it dry, and then apply repellent. Do not use products that contain both sunscreen and repellent.
  • Do not spray repellent on the skin under clothing.
  • Consider using clothing and gear (such as boots, pants, socks, and tents) that are treated with permethrin (an insecticide). You can buy pre-treated clothes or treat your own clothes. If treating items yourself, follow instructions carefully. Do not use permethrin directly on skin.

Consumer Reports recently put out a review of repellents. It can be found here. The publication's writers noted that “choosing the right repellent matters: Our top products warded off all three of those insects for at least seven hours, while some of our lowest-scoring ones failed almost immediately, especially against Aedes mosquitoes.” That's the main mosquito (see above) that carries Zika. So shop carefully!

I’ve been bitten, and now I have Zika symptoms. What should I do?

If you are pregnant, you should immediately get to a doctor who can run a diagnostic test and start monitoring you. Even though there is nothing that can be done at the moment to decrease a fetus's chances of being affected by microcephaly, there are a lot of researchers working on understanding Zika around the world, and it's possible they may come up with something at any time. There is also the issue of your own health and how the combination of the stresses of being pregnant and being infected [with] Zika may affect you. The CDC is tracking all women in this situation and said in a recent conference call that there were a dozen or so “adverse outcomes” among the women but did not provide any details.

If you are a woman and not pregnant and your symptoms are mild, there is probably no need to do anything, except if you had been previously trying to conceive a baby, your doctor may tell you to hold off. If you are a man and your symptoms are mild, there is probably no need to do anything either, but you should make sure to use condoms or not have sex for the next six months. More information about Zika and sexual transmission can be found here. If you are a woman or man and experiencing muscle weakness or other types of neurological issues, that warrants a call or visit to the doctor as you may be among the rare cases with serious complications with Zika.

I'm going to risk it and take my vacation in an area where there are active Zika mosquitos. Anything special I need to know about what to do when I get back?

The CDC says that even if you do not feel sick, you should take precautions to prevent mosquito bites for at least three weeks to minimize the chances that you'll pass on the virus to uninfected mosquitos. That's right — health officials are not only concerned about mosquitoes infecting you but you infecting mosquitoes. The logic behind that: If you have the virus in your blood, there's a chance a mosquito could pick it up — and carry it to another human.

How countries are combating the Zika virus

A health ministry worker fumigates a house to kill mosquitoes during a campaign against dengue and chikungunya and to prevent Zika infection in Managua, Nicaragua October 27,2016. REUTERS/Oswaldo Rivas (Oswaldo Rivas/Reuters)

This post has been updated.

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