TIME Exercise

More Exercise Isn’t Always Better, Study Shows

Men and women run on treadmills at a fitness gym in the West Bank city of Ramallah on June 25, 2012.
Men and women run on treadmills at a fitness gym in the West Bank city of Ramallah on June 25, 2012. Abbas Momani—AFP/Getty Images

The latest research shows there may be an upper limit to how helpful exercise can be on your heart

It’s probably not news to you that Americans just don’t exercise enough. Less than half of us meet the recommended amount of weekly physical activity—despite research that shows exercise can be just as effective as drugs in some cases to treat diseases such as diabetes. So why don’t we prescribe exercise in specific doses, like we would a drug?

In order to do that, you need to know exactly how much activity produces how much benefit, and whether there’s an upper limit, at which point the helpful effects either start waning or begin to do more harm than good. That’s what Paul Williams, a staff scientist at Lawrence Berkeley national Laboratory, and his colleagues wanted to know—and they found out in a new report published in Mayo Clinic Proceedings.

MORE: Short Bursts of Exercise Are Better Than Exercising Nonstop

Williams started with a group of heart-attack survivors who had been enrolled in either the National Runners’ Health Study or the national Walkers’ Health Study. The two studies were designed to measure what impact—measured in deaths due to heart disease—differing amounts of physical activity could have. “The notion that there was increased risk for people at high exercise has been around for a while, but the first thing that came into my mind was that there was something unusual and maybe something wrong about the data,” Williams says. “So I was hesitant to proceed.”

But as the data continued to emerge, it began to appear that exercise, like any other prescription, could be dangerous in high doses. Those who had had heart attacks and ran more than 30 miles a week or spent more than six hours in vigorous activity weekly were at an increased risk—by up to twofold—of dying from a heart event. “I certainly expected a point of diminishing return, but I wasn’t expecting to see the increase in mortality,” says Williams.

MORE: An Hour of Exercise Can Make Up for a Day of Sitting Down

In contrast, those who exercised moderately—which is to say more than the admittedly low recommended minimum but not as much as the extremely active—lowered their risk of heart-related death by 63% compared to those exercising the least.

“I would say the gains of being active are substantial,” says Williams, “but up to a certain point.” The results held after his team adjusted for the potential effects of age, diet and medication.

MORE: Exercise Snacking: How to Make 1 Minute of Exercise Work Like 30 Minutes

Williams stresses that the results only apply to a relatively small group—people who have a history of heart disease and who exercise at high levels—but he’s currently studying the same thing in the general population to see if similar trends are at work. The data could form the foundation for a prescription-based approach to exercise, as researchers become more familiar with how much exercise can influence factors that affect our health. For now, says Williams, “The message is that at least for heart attack survivors, more is better—up to a point.”

TIME Mental Illness

Why We Aren’t Better At Preventing Suicide

Robin Williams attending the Broadway Opening Night After Party for 'Bengal Tiger at the Baghdad Zoo' at espace in New York City
Robin Williams attending the Broadway Opening Night After Party for 'Bengal Tiger at the Baghdad Zoo' at espace in New York City Walter McBride—Corbis

Robin Williams' tragic death re-ignites long-asked questions about why it’s so challenging to identify and help those at highest risk of self-harm

Robin Williams’ death has served as a stark reminder that we have a long way to go in helping people at serious risk for self-harm. Part of the challenge, say experts, is that despite their stigma, suicidal thoughts are quite common, particularly among people who are depressed. “Suicidal thinking is common and widespread, especially among people with mental illnesses,” says Dr. Dost Ongur, chief of psychotic disorders at McLean Hospital and a psychiatrist at Harvard Medical School. “Yet we don’t have good ways of deciding who is at genuine risk, and who is suffering but who won’t go through with hurting themselves. The reality is that there is no established way of saying this person is at higher risk than that person.”

It’s not that anyone is expecting that a simple blood test or brain scan will provide the answer; the machinations of the body and mind are too complex for that. But as researchers learn more about the brain processes that lay the foundation for things like depression or addiction, they are moving toward developing a suite of tools that could help to at least triage people who are most vulnerable to harming themselves. “It’s something that comes over people; it can last hours or days, but not forever. If you can keep somebody safe during that period, it would pass,” Ongur adds. “The depression would remain, and the substance abuse would remain, but the intense feeling of not being able to go on would pass.”

MORE: Suicide in America: The People who Answer the Phone

Identifying people who might be especially vulnerable to those episodes could be a first step in preventing suicide attempts. In July, scientists reported finding that a gene involved in tamping down a stress response is different among those who have tried to end their lives compared to those who had not. The gene is integral to activity in the brain’s prefrontal cortex, which is responsible for things such as impulse control and reining in negative thoughts. It was in short supply in patients who reported suicidal thoughts.

Another group, led by John Mann at Columbia University, is focusing on the brain chemical serotonin, known for its role in mood disorders, and at Harvard, researchers are exploring the use of a bedside test that can probe the brain of patients with mental illnesses for clues to suicidality. All of these strategies, says Ongur, could help to shed more light on the black box that lies at the intersection of thought and action. “We don’t have a good framework for explaining what happens in the moments when a person is preparing to commit suicide.” That provides a window of opportunity for potentially life-saving interventions.

MORE: Robin Williams: The Comic Who Was Hamlet

Mental illness and substance abuse—both of which are correlated with suicide—are treatable, and could be the first step toward shifting patients away from self harm. Strengthening relationships can be another important factor. “The sponsor in AA is an example, a psychotherapist is another example and family relationships are other examples. We live in a relational world and people consider the impact their actions have on people important to you,” Ongur says.

But strengthening such relationships also requires a shift of a different kind, a societal change in how we perceive mental illness and react to those affected. “One of the big issues remains the stigma of mental illness, especially suicide,” says Ongur. “We are still dealing in a very real way with suicide not being something that is talked about openly and commonly. I saw a comment that the best tribute to Robin Williams would be talking more openly about suicide and making it part of a national conversation so that more research can be done and more people can be helped.”

TIME Mental Illness

Robin Williams’ Depression Struggles May Go Back Decades

The storied comedian and actor Robin Williams had spent time at a rehab facility this summer to maintain his sobriety, his publicist said.

“This morning, I lost my husband and my best friend, while the world lost one of its most beloved artists and beautiful human beings,” Williams’ wife Susan Schneider said in a written statement on Monday afternoon. According to the local sheriff’s office, coroners believe Williams may have committed suicide by asphyxia, and the actor’s representative said he had been “battling severe depression of late.”

While the representative did not elaborate on the potential source of his recent depression, one-third of people with major depression also struggle with alcoholism, and Williams admitted to abusing both cocaine and alcohol during the height of his popularity in the 1970s as alien Mork on Mork & Mindy, which showcased his manic improvisational style. He quit using drugs and alcohol in 1983 and remained sober for 20 years after the birth of his first son.

But in a revealing interview in the Guardian, Williams admitted that while working in Alaska in 2003, he felt “alone and afraid” and turned to the bottle because he thought it would help. For three years, he believed it did, until his family staged an intervention and he went into rehab, he told the Guardian. “I was shameful, did stuff that caused disgust — that’s hard to recover from,” he said then.

He said he attended weekly AA meetings, and this July, People.com reported that Williams spent several weeks at Hazelden Addiction Treatment Center in Minnesota, for what his representatives said was an “opportunity to fine-tune and focus on his continued commitment [to sobriety], of which he remains extremely proud.”

Studies suggest that alcoholism and depression may feed each other. People who are depressed are more vulnerable to abusing alcohol than those who don’t experience depressive episodes, and those who drink heavily are also more likely to experience depression. The latest evidence also hints that the same genes may be responsible for both conditions, and depression is a strong risk factor for suicide. About 90% of people who take their own lives are diagnosed with depression or other mental disorders. Suicide is also more likely among baby boomers, according to 2013 data from the Centers for Disease Control and Prevention.

The coroner’s office is continuing its investigation into Williams’ death.

TIME Breast Cancer

Osteoporosis Drugs Do Not Prevent Breast Cancer After All

Some studies had hinted that the bone-building treatments may also have an added benefit in fighting tumors, but the latest study doesn’t support that connection

In recent years, several large studies involving tens of thousands of women found a potentially useful connection between bisphosphonates, the popular bone drugs, and a lower risk of breast cancer. But new research published Monday in JAMA Internal Medicine challenges that long-held belief.

In previous observational studies, women who reported taking medications like alendronate (Fosamax) or zoledronic acid (Reclast) to treat osteoporosis also seemed to have lower rates of breast cancer compared to women who didn’t take the medications. There was biological evidence to support the association as well – bisphosphonates were also correlated with lower rates of cell death and hampered cancer cell activity.

But Trisha Hue, an epidemiologist at the University of California, San Francisco, and her colleagues, wondered if the connection could truly be attributed to the osteoporosis medications, or whether there was something else about the women taking these drugs that could explain the cancer trend.

MORE: Combining Bone-Building Drugs Key to Making Bones Stronger

Indeed, when they focused their attention on two studies that randomly assigned women to either a bisphosphonate or placebo, and followed them for up to four years, they found no difference between the women taking the drug and those who did not when it came to their breast cancer rates.

So why the strong connection in previous studies? Hue points out that those analyses, which were not randomized controlled trials, but rather observational studies, could not account for the fact that the drug-taking group may have been biased in some way. And in fact that’s likely what occurred – women who are prescribed bisphosphonates have low bone mineral density, and they also have low levels of the hormone estrogen, which is known to fuel tumor growth. So the earlier studies were not finding a correlation between bisphosphonate use and a lower risk of breast cancer, but instead were picking up the fact that bisphosphonate users were likely to have lower rates of breast cancer to begin with.

MORE: How Often Do Women Really Need Bone Density Tests?

It’s not the first time the benefits of the bone drugs have been called into question. In 2011, some studies found that the therapies could increase the risk of rare bone fractures in the strong bones such as the thigh.

While some doctors and patients may have turned to the bone-building drugs to potentially avoid getting cancer, Hue says “our take-home message is that if you are already on bisphosphonates for prevention of fractures, it’s very effective for preventing fractures. But they shouldn’t be taken specifically for the primary prevention of breast cancer.”

TIME Infectious Disease

We’re Getting Closer to Vaccines and Drugs for Ebola

Researchers have developed vaccines and treatments that show promise in fighting Ebola in animals, so is the outbreak a good opportunity to test them in people?

On Monday, National Institutes of Health immunologist Dr. Anthony Fauci told CBS This Morning that his research team is working on a vaccine to prevent Ebola, which is completely effective in monkeys, and will be tested in humans in September. And he’s not the only one developing a treatment for the deadly disease. The question is: Should experimental treatments be rushed into practice, given the breadth of this outbreak?

For the nearly 1,400 people who have been infected with Ebola, there isn’t much they can rely on to help them battle the vicious virus. Because the virus hones in on the liver and disrupts the formation of liver cells, which affect blood clotting, people eventually die from shock, when their blood pressure drops too low due to the build up of microscopic clots in the vessels. The only thing that can improve survival is intervening early with proper hydration and nutrition to keep the circulation strong.

But there are several promising interventions in the pipeline, all of which have been very effective in fending off the virus in monkeys, who experience the same symptoms and disease course as humans. Most of these vaccines and drugs, however, have not passed even the Food and Drug Administration’s (FDA) more lenient standards for therapies against exotic viruses like Ebola.

Should drugs get rushed to market?

Normally, companies must prove that a therapy or drug is safe and effective in people through rigorous clinical trials, but no trial would allow participants to ethically get infected with Ebola, given that it’s mortality rate ranges from 50% to 90%. So the FDA recently approved a different pathway for such products in which companies can first prove that the disease progresses similarly in an animal model as it does in people, and that the product is safe when tested in healthy people.

MORE: Picturing Ebola: Photographers Chase an Invisible Killer

Only one of the Ebola vaccines, which uses the cold virus as a vector to introduce the Ebola antigens, has reached the second stage, and public health officials are likely reluctant to introduce them widely in west Africa given their untested status and the fear and suspicion of western medicine that already makes the outbreak so difficult to contain.

“To bring a strictly experimental approach to this population – most people think that’s not a good idea, and not doable,” says Dr. Heinz Feldmann, chief of the laboratory of virology at the National Institute of Allergy and Infectious Diseases.

In order to even consider using such unapproved drugs in the crisis, they have to be requested. So far, neither the governments of the west African countries affected, WHO, nor humanitarian groups like Doctors Without Borders have done so. If they did, then regulatory officials in the U.S. would discuss whether they could be provided on a “compassionate use” basis.

Testing the vaccine on a human

That happened in 2009, when a German researcher received the shot after accidentally pricking herself while working with Ebola in the lab. The immunization she got was developed in 2005 by Feldmann and his colleagues, including Thomas Geisbert, professor of microbiology and immunology at the University of Texas Medical Branch at Galveston. The vaccine both protects against Ebola infection and treats those who are recently infected with the virus.

While it’s not clear whether the lab workers was actually infected – she got the shot 40 hours after the accident – she did not develop symptoms and did not show evidence of the virus in her blood.

“There’s just no financial incentive”

Feldmann says there are other strategies that look equally promising — but taking the next step of testing the products in people is proving more difficult, says Geisbert. “Globally, [Ebola] is not a huge problem in terms of infectious diseases in general. It’s devastating and sad for the people involved but it’s a small market for big pharmaceutical companies. There’s just not a financial incentive to develop a drug or vaccine.”

Unfortunately, it often takes outbreaks like the current one in west Africa, which is the largest in Ebola history (see Infographic: Ebola By the Numbers), to ignite interest in developing treatments. That, Feldmann notes, and the fear that a virus like Ebola could be used as a form of bioterrorism. “The fact is that biothreat countermeasure activities are what pushed multiple governments to do this work,” he says. Some of that investment may pay off in public health benefits, however, since a bioterror event is essentially an intentional and concentrated outbreak. Geisbert recently received a $26 million grant from the National Institutes of Health to study the three strategies, including in combination, to take the interventions to the next step.

And while an outbreak might seem like an ideal opportunity to test new treatments, it may actually be of little use, and may even do more harm than good. “My concern is that if you give the treatment to people in late stage disease, and if the person dies, then everybody is going to blame whatever was given,” says Geisbert. “If the person survives, you may never know if the product worked because it was somebody who was going to survive anyway, without the drug.”

Feldmann agrees. “People like me and others who have worked for years in vaccines and countermeasures are frustrated. But on the other hand, we don’t want to make a step that isn’t well thought through, and ruin the whole approach in the future.”

TIME Infectious Disease

Containing Ebola Is Extremely Labor Intensive, Former CDC Researcher Says

GUINEE-HEALTH-EBOLA
Members of the Red Cross provide information on Ebola to residents in Conakry, Guinea on April 11, 2014 at the start of the largest Ebola outbreak in history CELLOU BINANI—AFP/Getty Images

It's not about high-tech solutions but good old-fashioned legwork

Given the fact that the Centers for Disease Control and Prevention (CDC) is now urging Americans to avoid non-essential travel to Sierra Leone, Liberia and Guinea, which are battling the largest outbreak of Ebola in history, and the Peace Corps has pulled out its volunteers from the region, the key to bringing the epidemic under control will rest not with the highly trained scientists flown in from around the world, but with local volunteers.

In outbreaks like this, which has so far claimed more than 720 lives, the only way to control the spread of disease is by ensuring that anyone who is infected is isolated in a hospital, and that anyone they contacted are also monitored for symptoms. “The main way we have of controlling the outbreak is by preventing further spread of cases,” says Dr. Eileen Farnon, associate professor of medicine at Temple University School of Medicine. “You have to take people who are symptomatic out of the community so they don’t continue to spread disease.”

MORE: Here’s What You Need to Know Now About the Ebola Crisis

In 2007, Farnon, then at the CDC, traveled to the Democratic Republic of Congo and Uganda to help those nations battle smaller Ebola outbreaks. Farnon helped local health officials coordinate contact tracing, which involves asking every infected patient for a list of people they had contact with since they started experiencing symptoms, and then finding and monitoring those contacts for 21 days. “As you can imagine, the more infected patients there are, the number of contacts really grows exponentially,” she says.

The follow-up required an army of volunteers to visit the contacts daily during the incubation period, often taking their temperature and asking them about any unusual health symptoms. If people started showing signs of illness, the volunteers were responsible for contacting a hot line and arranging for them to come to a hospital for further testing and possibly isolation if they were infected.

MORE: Everything You Need to Know About the Deadly Ebola Virus Outbreak

Such contact tracing is also occurring now in West Africa, but it’s likely more challenging because of the denser and more fluid nature of the populations there, says Farnon. In the Democratic Republic of Congo and Uganda, the outbreaks occurred in remote regions and the contacts weren’t mobile and potentially infecting others in densely populated places like airports.

Farnon guesses that if contacts in the current outbreak mention that they are intending on traveling to another country, the health workers will likely discourage them from doing so, but that some, if they aren’t feeling sick, may still continue with their trip. That’s why national health officials need to coordinate screenings at border crossings to ensure that people who become ill are identified and cared for before they can spread the virus.

MORE: Infographic: Ebola By the Numbers

Farnon says there are social challenges as well. “People in the community will realize early on that patients who get admitted to the hospital, usually late in their infection, may die. And many start getting fearful about going to the hospital because they think it means they are going to die,” she says. While there are no treatments for Ebola infection, early care with proper hydration and nutrition can keep patients strong enough to overcome the virus. But even patients who survive are stigmatized because their neighbors think they are still contagious. Farnon says her groups provided a volunteer to accompany patients back to their homes to help them and their community to understand that they were no longer a threat.

The volunteers were the key to keeping the virus contained, says Farnon, and contact tracing, while labor intensive, was the key to managing the outbreaks in which Farnon was involved—and certainly essential to the west African situation as well. “The village health workers and volunteers are the primary means of getting messages to communities, because they have the relationships with the communities and the ability to mobilize others to help people look for the signs and symptoms of Ebola,” says Farnon.

“It’s a huge logistical undertaking,” she says—but it’s necessary.

TIME Drugs

It’s Easy to Overdose on Tylenol, Study Warns

Tylenol Pills Spilling Out Of Bottle
Shelley Dennis—Getty Images

A new analysis from Consumer Reports calls out the Food and Drug Administration (FDA) for inconsistent and potentially dangerous labeling of acetaminophen painkillers

The rise in prescriptions and non-prescription use of painkillers in the U.S. is no secret – in the past decade, prescriptions for opioids have skyrocketed by 300%, making them the most prescribed drugs in the country.

And the consequences of that spike can be deadly, according to the latest report from Consumer Reports: nearly 17,000 people die each year from overdosing on painkillers.

Equally alarming is the rise in other popular painkillers that also have over-the-counter (OTC) versions. Acetaminophen, which includes Tylenol and other generic brands, causes more than 80,000 emergency room visits each year because people often aren’t aware they’re taking too much. The drug is found in more than 600 over-the-counter and prescription medications, such as allergy and cold remedies and sleep aids.

To address the potential for accidental overdose of acetaminophen, the FDA asked physicians earlier this year to stop prescribing more than 325mg of acetaminophen to patients, noting that there isn’t evidence that higher doses provide any additional benefit for relieving pain and that high levels of the drug are linked to liver damage. But the warning did not apply to OTC versions of the drug, which account for 80% of acetaminophen use in the U.S., and are still available in higher doses.

MORE: Tylenol and Panadol Prove No Better Than Placebo at Helping Back Pain

The Consumer Report authors also say that OTC drugs have inconsistent advice about how much acetaminophen is too much for people to take in a day. “We found recommendations varying from 1,000mg per day in some nighttime pain relievers to 3,900 milligrams in some products that combine acetaminophen with allergy drugs or cold and flu drugs. We think the labeled daily limit should be no more than 3,250 milligrams,” they write.

Regarding opioids, the authors call for the FDA to reconsider its December 2013 approval of Zohydro ER, a long-acting version of hydrocodone, over concerns that longer-acting forms are more likely to be misused and abused and don’t show any clear pain-killing benefit over shorter-acting medications. They advise doctors to consider starting their patients who need pain relief with short-acting opioids first, to better gauge whether these forms can provide enough pain relief.

For consumers, the report urges people taking opioids or acetaminophen to ask for and expect regular monitoring of their pain and other symptoms. If the pain isn’t going away, then continuing to take the medications isn’t going to help, and will only expose you to potentially harmful side effects.

TIME behavior

This Blood Test Can Predict Suicide Risk, Scientists Say

Researchers report encouraging advances toward a blood test that can pick up genetic changes linked to suicide

Behaviors can’t be reduced to your genes – they’re far too complicated for that. But genes can lay the foundation for making people more or less likely to respond and act in certain ways, and suicide may be the latest example of that.

In a paper published in the American Journal of Psychiatry, researchers led by Zachary Kaminsky, an assistant professor of psychiatry and behavioral sciences at Johns Hopkins University School of Medicine, found reliable differences in the activity of a specific gene among those who had committed suicide and those who had not. They conducted a series of tests to verify their result. First, they studied brain samples of mentally ill people and those not affected by mental illness, and revealed that a gene, SKA2—which is most abundant in the prefrontal regions of the brain that are involved in inhibiting negative thoughts and corralling impulses—was less active among those who ended up committing suicide than among those who had not. If there isn’t enough of SKA2, or if it isn’t working properly, then receptors that pull the stress hormone cortisol into cells to put a brake on the stress response also don’t work. That can lead to unchecked negative thoughts and impulsive behaviors, like a runaway car without brakes.

MORE: U.S. Special Ops Are Soldiers Committing Suicide in Record Numbers

The scientists also compared amounts of SKA2 among people with suicidal thoughts or those who had already attempted to kill themselves. Based on levels of the gene’s products in the blood, they could predict with 80% to 90% accuracy whether a particular participant had had suicidal thoughts or had tried to commit suicide.

The differences Kaminsky and his colleagues found isn’t a genetic mutation, but a change in how active the SKA2 gene is. Environmental exposures and life experiences can affect how and when genes are turned on or off. That’s what is happening with SKA2 in those who commit suicide; their gene is inhibited from doing its job of controlling their stress response and modulating it properly.

The work is just the first step in potentially developing a blood test for identifying people at highest risk of harming themselves, says Kaminsky. “We are not going to recommend screening everybody,” he says. “I don’t think that makes sense.” But among those at high risk of suicide, knowing that they also have a possible genetic tendency to react negatively to stress may help to them to get consistent support and more aggressive mental health services to help them cope with their stress and avoid more tragic outcomes.

TIME Pregnancy

The Connection Between Parks and Healthier Pregnancy

Trees can do a lot of good for your health, from lowering stress to encouraging you to spend more time outdoors exercising. But can it help expectant moms have healthier babies?

What mother-to-be doesn’t do her best to nurture her still-developing baby so he or she can be ready for the world after nine months? Eating right, exercising, and avoiding extreme amounts of stress are just some of the ways that expectant mothers can cocoon their babies in the healthiest environment possible. And now scientists say there’s another thing pregnant women can do to help their babies to emerge from the womb at a healthy weight.

Living near green spaces – parks, gardens, and even cemeteries – is associated with fewer low birth weight babies, according to a study published in the journal Occupational & Environmental Medicine. An international group of researchers analyzed data from nearly 40,000 singleton births in Tel Aviv, Israel from 2002 to 2006 and matched the mother’s address at the time of delivery with satellite images of the landscape to assess their relative “green-ness.” Women who lived in areas with more access to parks or gardens or green spaces were less likely to have children with low birth weight, a risk factor that can contribute to respiratory conditions, intestinal disorders and bleeding in the brain as well as more long term health issues such as diabetes, heart disease, bone disorders and possibly autism.

Because greener regions tend to be associated with higher socioeconomic status and more maternal education, both factors that also affect the rate of low birth weight, the researchers also adjusted for the effect of socioeconomic status, and still found an effect of the greener environments. But they did find a stronger association between less green space and more low-birth-weight babies among those in lower socioeconomic groups, which could reflect the influence of other factors, such as less healthy behaviors in those populations and greater exposure to air pollution, stress and other environmental factors that can influence pregnancy outcomes.

So living near parks alone can’t prevent low-birth-weight babies, but the findings suggest that it couldn’t hurt. And the authors note that other studies hints at why – being near parks may encourage physical activity and promote more social interactions that can provide support to relieve stress and depression. Green spaces also tend to have lower levels of pollution and other potentially harmful environmental compounds that have been linked to poor fetal development.

TIME Infectious Disease

Here’s What You Need to Know Now About the Ebola Crisis

After a passenger brought Ebola to Africa’s largest city, health officials are on alert for signs of the infection among passengers. Here's the latest

The Ebola outbreak has already led to more than 670 deaths in West Africa, but a man who became ill on a flight from Liberia to Lagos, Africa’s largest city, has raised alarms for public-health officials after he later died of the virus.

Liberia has closed most of its borders, and airports in Nigeria are now screening passengers arriving from foreign countries for Ebola’s symptoms, which include fever, headache, joint pain, lack of appetite, difficult breathing and sore throat. In its advanced stages, Ebola leads to diarrhea, vomiting and internal bleeding. While the airport screenings are meant to ease travelers’ minds, the reality is that the Ebola virus can’t be detected soon after infection — the first signs of the virus are red eyes and a rash, which could be caused by many different things. Plus, outgoing flyers are not being tested and its unclear at this point if over countries will follow suit. People have recovered from infection with the virus, but the mortality rate ranges from 50% to 90%.

(MORE: Here’s What It Will Take to Contain the Worst Ebola Outbreak in History)

Who can spread the virus?

The virus takes anywhere from two to 21 days to incubate and start causing symptoms, but Dr. Stephan Monroe, deputy director of the National Center for Emerging and Zoonotic Infectious Diseases at the U.S. Centers for Disease Control and Prevention (CDC), said during a telebriefing Monday that infected patients only spread the disease when they have symptoms. Because the virus is transmitted through direct contact with fluids like saliva or blood from infected patients, airport officials are essentially looking for passengers who might have severe vomiting, diarrhea or other bodily secretions that could reach other travelers.

Are Nigeria’s airport screenings enough?

Nigeria is screening incoming passengers for such symptoms and may also take passengers’ temperature. Nigerian officials have also created holding rooms to isolate patients or passengers who are suspected of being infected, so they can be triaged to further medical care.

But because some of the early symptoms of Ebola mirror those of other ailments, including malaria, CDC officials say the strongest way to contain spread of infectious diseases is by instituting travel restrictions at the source. That’s why Liberia has closed all its borders except for three land crossings where travelers can be screened and treatment services provided if needed.

Dr. Marty Cetrone, director of the division of global migration and quarantine at the CDC, said during the briefing that officials can also try to contain the outbreak by using questionnaires asking travelers at these checkpoints about their recent travel history as well as their potential exposure to the virus through friends or other close contacts.

How did this outbreak get so bad?

Health officials aren’t sure why this particular outbreak has led to a historic number of deaths, but note that social and cultural practices may be driving spread of the virus. In many of the communities where the virus remains active, there is still denial about the disease, and stigma associated with getting ill, which discourages patients from getting early hydration and nutrition that can help them to overcome the infection. While there is no treatment for the virus, these measures can lower the death rate for some. Funeral practices that involve touching the deceased may also help the virus move from host to host.

How at-risk are Americans?

Monroe says the risk of Ebola for U.S. citizens who haven’t traveled to West Africa remains low. There are no restrictions on travelers entering the U.S., but the CDC has issued a Level 2 travel advisory for people traveling to Guinea, Liberia or Sierra Leone, recommending that they avoid contact with blood or other bodily fluids that might contain the virus, and use the proper protective equipment to avoid infection. The advisory applies mostly to health care or humanitarian aid workers, who so far make up the largest group of people affected by Ebola. “[Transmission] involves not only touching the contaminated body fluid but introducing it through some mucous membrane or cut on the skin,” said Monroe.

For anyone who has recently traveled to those countries or might have been exposed to someone who was ill in that area, health officials are advising a 21-day fever watch to ensure that no active infection is occurring.

What if an infected person flies into the U.S.?

The CDC is also preparing for the remote possibility that a passenger from the region who is ill boards a plane and lands in the U.S. and starts infecting residents. The agency is informing its network of physicians in state and local public-health facilities about how to look for signs of Ebola. “We are sending Health Alert Network notices about the importance of taking steps to prevent spread of the virus,” said Monroe. That includes procedures on asking patients about their recent travel history, as well as using the proper personal protective equipment, such as masks, gloves and gowns if they suspect an Ebola infection.

They’re confident that these measures will be effective, since infection with a virus related to Ebola, Marburg, was successfully contained in the Netherlands with isolation and barrier procedures. No health care workers contracted the virus from that patient. Health officials hope that with the proper preparation and education, that record can apply to Ebola as well, if it makes it beyond the heavily affected countries in West Africa.

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