In early 2016, Zika virus was declared a global public health emergency after a massive outbreak in Brazil was linked to birth defects, and there were smaller epidemics in the Caribbean and other areas. Some people in the United States canceled vacations and trips, and some professional athletes decided not to attend the 2016 Olympics Games in Rio de Janeiro. Two years later, Zika virus seems to be all but forgotten.
The virus has actually been around since the 1940s, when it was first discovered in the Zika rainforest of Uganda. The virus is spread through the bite of an infected Aedes aegypti mosquito — a species that unlike other types of mosquitoes, bites during the day and night. It can also spread from a pregnant woman to her fetus during pregnancy or from a man to a woman during unprotected sex.
Most people who get infected with Zika virus don’t develop symptoms, or only have relatively mild symptoms such as a fever, rash, and joint pain. In pregnant women, the virus has been shown to cause birth defects like microcephaly, a condition in which a baby has an abnormally small head, an underdeveloped brain, and cognitive problems, among other issues. Some cases of Zika have been linked to Guillain-Barré syndrome and other long-term neurological problems. Guillain-Barré syndrome is a potentially life-threatening type of weakness and paralysis that may or may not be reversible. Although the infection itself is very mild, it can have severe and even fatal consequences for certain groups.
So where is Zika still a threat, and who needs to take special precautions? We spoke to two experts to find out.
If you are living or traveling inside the continental US, Zika is not an imminent threat — even in Texas and Florida, states that previously reported cases of Zika virus. There haven’t been any locally transmitted Zika virus cases in the US in 2018 so far, and only 21 cases in travelers returning from Zika-affected areas, according to the US Centers for Disease Control and Prevention.
These figures could change over the summer with a rise in the number of mosquitoes, but the experts said it’s likely that the Zika case counts for the US will stay low. “I wouldn’t advise anyone, including pregnant women, not to travel to previously Zika-affected areas in the US. … It’s definitely safe,” said Dr. Sarah E. Hochman, assistant professor of infectious diseases at NYU Langone Health in New York.
However, Puerto Rico does still have ongoing transmission of Zika virus. There have been 45 cases reported so far in 2018, but this number will likely increase by the end of the year. Pregnant women are advised not to travel to Puerto Rico, and those living in the country should take precautions to protect themselves from mosquitoes.
After 2016, cases of Zika plummeted in the Americas. Why? The prevailing theory is that most people living in places with high rates of transmission became immune to the virus.
“We believe that once you’re exposed to Zika you develop immunity to being reinfected, and if enough people are exposed you create herd immunity,” Dr. Albert Icksang Ko, professor of epidemiology at Yale University in New Haven, Connecticut, told BuzzFeed News. Herd immunity occurs when a high enough proportion of the population becomes immune to an infectious disease that they protect people who haven’t been infected or vaccinated. So in areas where Zika was rampant, vulnerable populations should have more protection.
Although there have been efforts to reduce the risk by controlling mosquito populations, that approach doesn’t really work, Ko said, “because in those regions we still have repeated epidemics of dengue and chikungunya.” Dengue and chikungunya are two other diseases carried by mosquitoes.
Other proposed interventions include breeding genetically modified mosquitoes that pass a lethal gene to their offspring, and a DNA-based Zika vaccine, but none of these have been rolled out.
Outside of the Americas, there are still regions with ongoing Zika transmission, primarily in Central Africa and South Asia. “There was an outbreak in Angola around Christmastime, and a few smaller outbreaks in South Asia, in countries like Vietnam and Thailand,” Ko said.
All that being said, many cases of Zika go unreported, so the actual number of cases may be higher. “The problem with Zika is that the majority of cases are asymptomatic, so there may be pockets of transmission in the Americas we still don’t know about,” said Ko.
It can be difficult to avoid mosquito bites, but there are steps you can take to reduce your risk.
“The most important thing is to be using some kind of insect repellent; the most effective ones contain DEET. You should also sleep in a building with screens, mosquito nets, and wear long sleeves and pants,” Hochman said. The CDC also recommends covering cribs and baby strollers with mosquito-proof netting and treating clothing with permethrin.
Before traveling, you should consult your health care professional to determine your risk — certain groups need to take additional precautions when traveling. If you think you were exposed to Zika during your travels, you can also take a blood or urine test to confirm a diagnosis.
Zika can be transmitted through unprotected sex from a man to a woman, even when the infected person has no symptoms. When traveling to areas with ongoing Zika transmission, sexually active individuals should use a condom during vaginal, anal, and oral sex.
The CDC states that pregnant women should not travel to areas with a risk of Zika infection. At this point, the experts said, it’s clear that a Zika virus infection during pregnancy increases the risk of birth defects like microcephaly.
If you are pregnant and you must travel to a place with ongoing Zika transmission, talk to your doctor about steps you can take to prevent infection.
Men infected with Zika can also spread the virus to their pregnant partner through unprotected sex. According to the CDC, the virus can stay in a man’s semen for up to six months after infection.
Travelers with a pregnant partner should avoid mosquito bites at all times. If they think they were exposed to Zika during their travels or experience any symptoms, they should see a doctor and get a Zika virus test. To avoid transmission and putting the developing fetus at risk, couples should use a condom during sex for the remainder of the pregnancy, said Hochman.
Any couple or person who is planning on getting pregnant during or after going to a Zika-affected region should talk to their doctor. It is possible for the Zika virus to stay in a man’s semen and infect a partner who is trying to become pregnant.
If you are a couple traveling together or a man traveling, the CDC recommends waiting to conceive until at least six months after returning from Zika-affected areas or after the start of symptoms, if you develop any. The couple should also use condoms during this time.
If you are a woman traveling to Zika-affected areas and planning on getting pregnant in the near future, you should wait at least two months after returning or showing signs of Zika virus, to try conceiving.
In general, it’s a good idea to avoid mosquito bites wherever you live or travel. “Any place where you may be exposed to mosquitoes, you’re putting yourself at risk not just for Zika but many other mosquito-borne infections,” Hochman said. These include yellow fever, West Nile, dengue, chikungunya, and malaria, depending on where you are in the world.
So in conclusion: Be aware of Zika, but not overly concerned. The virus is still around, and there’s still a risk of infection depending on where you live or travel. It’s important to stay educated and take the right precautions to remain healthy.