TIME ebola

See How Ebola Drugs Grow In Tobacco Leaves

The drug that saved the lives of American aid workers from Ebola was made by plants

It would be an understatement to call ZMapp a “sought after” drug. Ever since it brough tback two Ebola-infected aid workers from the brink of death, demand for the drug—which has not been approved by the Food and Drug Administration and was made available on an emergency use basis—has boomed. The trouble is, there’s no supply.

The doses administered to the U.S. aid workers exhausted a nearly nonexistent supply, according to its manufacturer, Mapp Biopharmaceuticals. But that’s not because it takes a long time to manufacture the antibodies that make up the ZMapp cocktail. ZMapp is taking longer to produce in large quantities because one of the three antibodies in the cocktail doesn’t grow well in the plants—which is how ZMapp is produced.

The process involves growing tobacco plants, not in the acres of fields earmarked by tobacco companies for their cigarettes, but in a controlled environment in a greenhouse, for six weeks. Then, the leaves of the plants are injected or infused with a plant bacterium that carries a valuable payload — the genes for the antibodies that can bind to and neutralize the Ebola virus. The plant cells treat the new genes as one of their own, and start making the antibody. It takes about 14g of these antibodies to treat a patient, says Yuri Gleba, CEO of Icon Genetics, the German company that pioneered the platform, and to produce that much requires around 78 tobacco plants and about seven to 10 days.

A team led by Gleba is helping Mapp Biopharmaceuticals to optimize that production and to make the entire process more efficient so it requires fewer plants. “If everything is properly optimized, those plants can be full of that antibody,” he says. (Mapp officials declined to comment for this article on the status of their ZMapp production.)

MORE: Ebola Treatment May Emerge From Drug For Another Virus

Why plants? The time it takes to grow a plant is less time than it takes to genetically engineer a mouse or other rodent to produce human antibodies, which is how such products have been made in the past. It’s also less expensive. Plant-based manufacturing represents a promising new way of producing drugs that could cut the time it takes to bring critical medications, such as a flu vaccine during a pandemic, to a large number of people. Researchers have used the technology to develop a vaccine against norovirus, the infection that plagues cruise ships, for example, that is being tested now.

Here’s what that process looks like.

MORE: Potential Vaccine Shows Some Promise, but the Spread of Ebola Is Accelerating

 

 

TIME Sex

Does Teen Sexting Lead to Earlier Sex?

teen sext text
Getty Images

The latest research teases apart whether sexting promotes more sex, or whether having sex makes sexting more likely

While plenty of studies have linked the sending of sexually explicit messages or naked pictures to a higher incidence of sex and risky sexual behavior, most of those studies didn’t follow the same children over time. That means they studied sexting habits in one group of children, and sexual behaviors in another, older group a year or so later. So it’s possible that other factors could explain the relationship that had nothing to do with the sexting.

To address that issue, Jeff Temple, from the department of obstetrics and gynecology at University of Texas Medical Branch, collected data from a group of nearly 1,000 high school students in Texas over six years. The students answered questions about dating, dating violence and other behaviors as sophomores and then as juniors. Temple then compared the answers.

MORE: Review: Men, Women & Children Shows How Sexting Is Ruining America

Reporting in the journal Pediatrics, he says that those who sexted as sophomores were 32% more likely to have had sex in the following year than those who did not, supporting earlier data. But Temple was also able to break down the types of sexts the students primarily used, from those who actively sent naked pictures to those who only received or asked for them. Those who only received sexts did not show a statistically significant higher risk of having sex, but those who asked for a sext were nearly 10 times more likely and those who were sent a sex were 5.3 times more likely to send one themselves. And students who sent sexts were the most likely to have sex in the following year.

“So basically if a parent saw his kid had asked for a sext, that in and of itself isn’t related to sexual behavior unless that kid also sent naked pictures of himself,” says Temple.

The data also showed that sending sexts, while associated with a higher chance of having sexual intercourse, was not linked to an increased incidence of risky sexual behavior, such as unprotected sex, having multiple sexual partners, or using alcohol or drugs before sex. “That was surprising but it might mean that sexting is not limited to just at-risk kids,” he says. “Sexting may be becoming part of sexual development, and therefore it involves a cross section of all adolescents.”

MORE: Sexting in Middle School Means More Sex for Preteens and Teens

Temple admits that the data need to be confirmed with other studies; the reports on sexting and sex were self-reported by the students, which could affect their reliability. But the rates of sexting, along with sexual intercourse, fall in line with national surveys so are likely to be valid, he says.

MORE: Non-Consensual Sexting: The Hot New Way to Make Someone Really Uncomfortable

If sexting is indeed part of the new normal of sexual development, then it could be a sign of those who are more ready for sexual activity or more receptive to it, he says. Studies show that up to a third of adolescents are involved in sexting, and they may be good candidates for education about safe sex and the dangers of unprotected sex. “If sexting does predate sex, then it’s of public health importance. It becomes a marker of sexual activity and it could be a good opportunity to talk to them about safe sex prior to them having sex and preventing early sexual debut and risky sexual behavior,” he says.

TIME medicine

New Genes Found that Determine Your Height

The latest analysis doubles the number of genes connected to height

How tall you are is strongly related to the genes you inherit, and previous studies suggested that as much as 80% of the variance in height among people is due to their DNA.

And in the largest genetic study of height-related genes to date, scientists involved in the appropriately titled GIANT consortium (Genetic Investigation of Anthropometric Traits) identified 423 genetic regions connected to height — which could explain as much as 60% of that genetic component.

Dr. Joel Hirschhorn, leader of the GIANT consortium at Boston Children’s Hospital, Harvard Medical School and the Broad Institute of MIT says that for a trait like height, which isn’t determined by a single gene but likely the combined effects of multiple genes involved in multiple different processes from bone growth to cell growth, the new findings are like finding biggest nuggets of gold in a riverbed. The latest analysis, published in the journal Nature Genetics, describes the gene variants most commonly shared among people (not the rare mutations) that likely contribute to height.

They emerged from a sweep of the genomes of more than 250,000 people of various heights, and from correlating their stature with their genetics. Many of the known and familiar factors related to height, including those dealing with skeletal growth and collagen that are mutated in people with medically short stature, for example, appeared in the study, confirming their role in determining how tall people get.

But there were also some surprises — genetic regions that previous had never been thought to be related to height, including a gene known to be involved in cell growth but not in skeletal functions. “It’s a mix ranging from completely known things, to those that make sense to things that are completely surprising and things we don’t even know what to think about them,” says Hirschhorn.

What the group has identified are gene regions of interest, and a new round of studies will have to delve deeper into those areas to isolate specific genes — and the proteins they make, such as growth factors, enzymes, or other agents — that are actually responsible for determining height. But it’s a critical first step, and could lead to potential new ways of treating medical conditions of short stature or gigantism that can have health negative health effects on the heart and joints.

TIME ebola

Ebola Contact Found By Dallas Law Enforcement

A scanning electron micrograph of Ebola virus budding from the surface of a Vero cell of an African green monkey kidney epithelial cell line.
A scanning electron micrograph of Ebola virus budding from the surface of a Vero cell of an African green monkey kidney epithelial cell line. NIAID—EPA

"This person has not committed a crime; he is a low risk individual"

Updated Sunday, Oct. 5

A once-missing homeless man believed to have had some level of contact with Dallas Ebola patient Thomas Duncan was found Sunday, NBC news reports.

The man’s temperature was taken yesterday, and he was asked to remain available for temperature checks today and for 21 days, but left, said Judge Clay Jenkins, who is leading Dallas’ emergency response efforts. The Dallas County sheriff’s office and police department were searching for the man.

“This person has not committed a crime; he is a low risk individual. We want to move him to a comfortable, compassionate place, and care for his every need while we monitor him throughout the monitoring period,” said Jenkins during a news conference Sunday. “He is asymptomatic. We are doing this as a precautionary measure.”

The man belongs to a group of 38 people who are having their temperatures taken twice a day and asked about any possible Ebola symptoms for 21 days, since they may have had contact of any kind, even indirect, with Duncan. Centers for Disease Control (CDC) director Dr. Tom Frieden said that 10 people who had more direct contact with Duncan are being watched the same way.

Seven of the 10 are health care workers who were at the hospital while Duncan was treated, and three are from his family or community. Four of Duncan’s close relations, including his female partner and three young men living in the apartment where he stayed prior to falling ill, have been quarantined. One of these individuals, however, did not have direct contact with Duncan; however, he may have wanted to stay with his family.

The four were moved on Saturday to a more secure location and none are showing any symptoms of infection. One of the young men is able to play basketball at the new residence, said Jenkins.

Duncan’s condition worsened on Saturday, and he is now in critical condition at Texas Health Presbyterian. Frieden said any decisions about whether Duncan would be treated with any experimental therapies would be decided by Duncan, his family and his doctors. One potential treatment initially makes patients worse before they improve, and none have been approved by Food and Drug Administration because none have been tested for safety and efficacy in human patients.

The news about the missing contact in Dallas comes on the same day that health officials ruled out a potential case of Ebola in a traveler arriving at Newark airport. That passenger’s symptoms and tests did not indicate he was infected with Ebola, said Frieden. But concern about the disease has escalated since Duncan’s diagnosis. The CDC received an average of 50 calls or emails daily from doctors, hospitals or health departments about potential Ebola cases, before Duncan’s case, and that volume has jumped to about 800 inquiries a day.

Frieden stressed that keeping Ebola from spreading in the U.S. will require a combination of strong public health efforts within the country — making sure health care providers ask about recent travel history for any patients presenting with fever and other symptoms of Ebola, and quickly isolating them if they have been to West Africa — and maintaining efforts to stop the epidemic in Guinea, Liberia and Sierra Leone as well.

So far, CDC-trained screeners at airports in the three affected countries have removed 77 from boarding planes headed to the U.S., and those temperature-taking efforts, along with asking passengers about any potential contact with Ebola patients, remain critical, said Frieden. But aid efforts to help health officials in Africa are just as essential to protecting the U.S. as well.

If people are prevented from leaving or entering the three countries struggling with the Ebola epidemic, he said, then the disease will continue to rage there and potentially pose a larger threat to the global community in coming months. “As long as cases continue there, there is the possibility that someone will travel, and infect someone else in this country or other countries,” he said. “An outbreak anywhere is potentially a threat everywhere.”

Frieden will meet with President Obama this week to discuss global efforts to contain Ebola in Africa.

TIME ebola

U.S. Ebola Patient ‘Fighting for His Life’

Residents Quarantined In Dallas Apartment Where Ebola Patient Had Stayed
Dallas County, County Judge Clay Jenkins walks with an acquaintance from the apartment where an Ebola virus patient was staying at the Ivy Apartments on October 3, 2014 in Dallas, Texas. Joe Raedle—Getty Images

The four people in the apartment with an Ebola patient before he became ill have been moved to a secure location, Dallas health officials say.

Updated Sunday, Oct. 5

The first person to develop the Ebola virus in the United States is in critical condition, a spokesperson for the Dallas hospital where he’s being treated said Saturday. The patient, Thomas Duncan, was previously listed in serious condition, and his change in status means his health is degrading.

“We understand that his situation has taken a turn for the worse,” Centers for Disease Control and Prevention Director Dr. Thomas Frieden said of Duncan’s condition in a Sunday press conference. Frieden added that Duncan is “fighting for his life.”

The news of Duncan’s failing health comes as his partner and the three young men living with her in the Dallas apartment where Duncan stayed before he became sick were moved to a temporary residence. Dallas County Judge Clay Jenkins, who heads up the city’s emergency response, drove the four individuals to their new home on Friday night. Jenkins said on Friday that he hoped to find them accommodations with appliances that would make the four family members more comfortable during their quarantine, such as their own washer and dryer.

In a Saturday news conference, Frieden said CDC and local health officials are now monitoring 40 people who had some level of contact with Duncan, including nine who had direct contact with Duncan. It’s not clear how many of those are health care workers or patients at Texas Health Presbyterian Hospital, where Duncan is being treated, and how many are community members, including those who live in the apartment complex. On Sunday, a homeless man with whom Duncan had some level of contact was found after being sought by officials for monitoring.

Medical waste generated by Duncan during his stay at the hospital, including gowns and personal protective equipment worn by health care providers caring for him, remain at the hospital, said Dr. David Lakey, commissioner of the Texas Department of State Health Services. The waste removal company has now secured the proper Department of Transportation hazmat permits to transport the waste, and is set to do so on Monday.

Duncan originally went to the hospital on Sept. 25, but was released despite having told staff there he recently traveled to Liberia, the heart of West Africa’s Ebola crisis. He was re-admitted three days later when his condition worsened. While Texas Health Presbyterian Hospital originally blamed technical glitches for the failure in getting Duncan’s travel history to the right people, the facility walked back that claim Saturday, raising questions about the hospital’s procedures during what’s become the worst-ever Ebola outbreak.

TIME Sex/Relationships

How Previous Sexual Partners Affect Offspring

At least, if you’re a fly. But the research suggests that it may be time to take into account more than just DNA when it comes to our offspring

It’s a long-held belief among animal breeders that pure-bred progeny are best produced by females who have never mated before. Call it puritanical or ridiculous, but in breeding, it’s been a long-standing practice—even though there has never been much science to back it up. Now, however, researchers at University of New South Wales in Australia believe they may finally have some evidence to give that notion some scientific support.

Working with flies, Angela Crean, a research fellow at the evolution and ecology research center, picked up on her mentor’s work of looking at how male factors can influence offspring outside of the DNA in his semen.

“The genetic tests showed that even though the second male fertilized the eggs, the offsprings’ size was determine by the condition of the first male,” she says of her findings, published in the journal Ecology Letters. “The cool thing is that the non-genetic effects we are seeing are not necessarily tied to the fertilization itself.”

Cool, or really disturbing. The implications of the study are that any mates a female has had may leave some legacy—in the form of physical or other traits that are carried in the semen (but not the DNA-containing sperm)—that could show up in her future offspring with another mate.

While there’s a growing body of work showing that a mother’s diet, her smoking status, and other lifestyle habits can have an influence on her offspring, the data on similar factors on the father’s side is just emerging. With flies it’s known, for example, that males who eat a maggot-rich diet while they’re mere larvae, develop into larger than average adults, and on top of that, sire larger than average offspring as well. Males fed a meager maggot diet tend to be smaller have have smaller progeny.

Eager to learn how this was happening, Crean conducted a series of mating experiments with female flies when their eggs were immature. At that stage, the eggs are more receptive to absorbing factors in semen, but because they aren’t fully developed, they can’t be fertilized and won’t result in baby flies. When she and her colleagues “mated” these females with males who were larger, then allowed the females to actually mate with smaller males once they were mature, the offspring turned out to be large, just like the first males the females had sexual contact with. Genetically, they were the offspring of the second, smaller male, but physically, they resembled the larger males.

The same was true when they reversed the experiment and first exposed the females to smaller flies and then mated them with the larger ones.

To be sure that the was indeed due to something in the semen, Crean repeated the studies with an unfortunate group of male flies who had their genitalia glued down so they could not pass on any semen during their encounters. (“It’s horrifying but seemed nicer than cutting them off,” she says.) When these males, both large and small, were the first “mates” for females, their size did not have an effect on the offspring when the female mated with her second mate and had offspring. In other words, those offspring were large if the second male was large, and small if the second male was small.

Crean says the idea of a female’s previous mates having an effect on their offspring isn’t unheard of. In fact, this very idea, called telegony, was proposed by ancient scholars such as Aristotle but dismissed with the advent of genetics. But new findings about epigenetics — how our behaviors, such as diet, smoking and drinking — can affect our genes and how those changes can be passed on, make the idea of such non-genetic inheritance possible. “This could be seen as a maternal effect [such as diet or smoking] where the mother’s environment are her previous mating partners,” she says. “We have to realize that it’s not just DNA that gets passed on. It opens up the opportunity for all these other pathways that we had excluded.”

And while flies aren’t people, what are the chances that the same phenomenon is occurring in human reproduction? “It’s something we definitely don’t want to speculate about yet with humans,” she says. “There is no direct scientific evidence for that at all.” At least, for now.

TIME ebola

Ebola Patient in Texas Is Not Allowed Any Visitors

Thomas Eric Duncan remains in serious condition at a Dallas hospital

Thomas Eric Duncan remains in serious condition at Texas Health Presbyterian Hospital, kept under close watch by law enforcement officials. He’s not allowed any visitors, but is communicating with family and friends via phone.

In a news conference on Thursday, Dr. Tom Frieden, director of the Centers for Disease Control and Prevention, said CDC-trained health officials in Monrovia, Liberia, took Duncan’s temperature before he boarded a plane on Sept. 19 to begin his journey to the United States. As part of the screening process to prevent the spread of Ebola into this country, passengers’ temperatures are taken and those with fevers are pulled off the flight. Duncan’s temperature, according to Frieden, was 97.3 (or 36.3C) — normal.

Frieden said more than a dozen people from the countries most affected by Ebola were prevented from boarding flights to the U.S. in September. Duncan did not develop fever and symptoms until four days after he arrived in Dallas.

The four people in the apartment where he stayed are now under quarantine, prevented from leaving their home by a law enforcement officer stationed outside the complex. If any of the individuals violate the order, a formal court order will be issued. None of the people are symptomatic, but, said Dr. David Lakey, commissioner of the Texas Department of State Health Services, he “had concern about our ability to be confident that monitoring was going to take place the way we needed it to take place.” People who might have had contact with Duncan are being monitored with twice daily temperature checks and, he said, without elaborating on the reasons, “we felt this [quarantine order] was needed.”

Food is being delivered to the four people in the apartment and Lakey said a cleaning service had been found to thoroughly clean the residence as well. Health officials visited the apartment when Duncan was admitted to the hospital, and helped the residents bag Duncan’s belongings, along with trash and towels that he used. In an interview with Anderson Cooper 360° due to air Thursday evening, however, Duncan’s partner, Louise, with whom he stayed and is one of those quarantined, said the sheets he used were still on the bed. She and the other four people in the apartment were also instructed about how to decontaminate areas that Duncan might have touched, until more thorough cleaning could be done.

For now, Lakey said, “I have no intention to put other individuals under a control [quarantine] order.” Together with the CDC, the Texas health department is monitoring 100 people with daily temperature checks; most are unlikely to be at high risk of developing Ebola, and only about a dozen had direct contact with Duncan. The state is also investigating how Duncan could have been sent home after his first visit to hospital, when he had a fever and told the nurse that he had recently arrived from Liberia.

TIME Aging

How Moodiness and Jealousy May Lead to Alzheimer’s

Researchers say certain personality traits, like jealousy, worry, anxiety and anger, can double a woman’s chances of developing Alzheimer’s

We’re familiar with many of the brain-related factors that can contribute to Alzheimer’s disease—letting thinking networks go inactive, putting off exercise and healthy eating, having few social connections, enduring head injuries and genetic factors. But what about personality? Can the way you look at the world affect your risk of developing the neurodegenerative disorder?

Dr. Ingmar Skoog, professor of psychiatry and director of the research center on health and aging at the University of Gothenburg believes the answer is yes. In a paper published in the journal Neurology, he and his colleagues show that women with certain personality characteristics in middle age were twice as likely to have Alzheimer’s nearly 40 years later.

MORE: New Research on Understanding Alzheimer’s

“Getting Alzheimer’s disease is some sort of sum of a lot of different damages to the brain, and different things happening to the brain,” he says. “[Personality] is one of them.”

Specifically, a suite of features linked to what mental health experts call neuroticism showed the strongest connection to Alzheimer’s. Skoog and his colleagues tapped into a database of health information involving 800 women who were 38 years to 54 years old in 1968, when they filled in personality questionnaires and agreed to come in periodically to evaluate their cognitive functions. The personality evaluation placed women on a spectrum of neuroticism and extraversion; those showing more neuroticism included women who reacted more emotionally to events and experiences, worried more, showed lower self esteem and were more likely to express jealousy, guilt and anger. Those who were more extroverted showed high levels of trust, gregariousness and fewer emotional peaks and valleys.

MORE: New Insight On Alzheimer’s: What Increases Your Risk

At each of the four follow ups over the next 38 years, the women reported their stress levels—and women with higher neuroticism scores consistently showed higher levels of stress than those with lower scores.

Skoog believes that stress is the linchpin between the personality traits and Alzheimer’s dementia; previous studies have connected stress to dementia, and he says that the neuroticism characteristics are highly correlated to stress. “It seems like the personality factor makes people more easily stressed, and if people are more easily stressed, then they have an increased risk of dementia,” he says.

What’s more, when he controlled for the effect of stress, the association between neuroticism and Alzheimer’s disappeared, strengthening the idea that personality may lay a foundation for being more vulnerable to the effects of stress. Higher stress, particularly if it’s persistent as it is with certain personalities, can bathe the brain in hormones like cortisol. Those can damage blood vessels and cells in the brain that can then make Alzheimer’s more likely.

MORE: Scientists Are Getting Closer to a Blood Test for Alzheimer’s

The results hint that people can lower their risk of Alzheimer’s not just by keeping the brain active and improving social connections, as earlier work suggests, but by addressing stress-related personality factors as well. That, however, may require being aware of your later Alzheimer’s risk as early as during childhood, when personalities are forming. “Personality is something that occurs early in life, but you may be able to do something about it,” says Skoog. Especially when it comes to stress and how people respond to stress, interventions such as psychotherapy, for example, can help people to cope in healthier and less harmful ways.

He doesn’t believe that addressing stress and traits like jealousy and worry alone will protect a person from developing Alzheimer’s, but, he says, “it’s important to try to find as many factors as you can that contribute to common disorders. The more factors we can do something about, the more we can reduce risk quite substantially.”

TIME ebola

First U.S. Ebola Patient Identified

His sister identified him

The first patient to be diagnosed with Ebola in the U.S. was identified Wednesday as Thomas Eric Duncan.

Duncan’s sister Mai Wureh told the Associated Press it was her brother who is at the center of the country’s latest Ebola scare. Wureh said her brother went to the emergency room on Friday complaining of fever and a nurse asked about whether he had recently been in Ebola-affected countries. He said yes, but, according to Dr. Mark Lester, a clinical leader for Texas Health Resources, the “information was not fully communicated throughout the whole team.”

Duncan was sent home with antibiotics, and returned two days later in an ambulance with more severe symptoms. He is currently in serious but stable condition at Texas Health Presbyterian Hospital.

[AP]

TIME ebola

This Is the 21-Day Process for Stopping Ebola

Texas Hospital Patient Confirmed As First Case Of Ebola Virus Diagnosed In US
Dr. Edward Goodman, epidemiologist at Texas Health Presbyterian Hospital Dallas, and Dr. Mark Lester, Southeast Zone clinical leader for Texas Health Resources, answer questions during a media conference at Texas Health Presbyterian Hospital Dallas where a patient has been diagnosed with the Ebola virus on Sept. 30, 2014 in Dallas. Mike Stone—Getty Images

Experts are tracking anyone who could have come in contact with the first patient to be diagnosed in the U.S.

U.S. health officials were working Wednesday to determine whether the first diagnosis of Ebola on American soil is an isolated case—or whether the patient may have infected others.

The Centers for Disease Control and Prevention (CDC) dispatched a nine-person epidemiology team to Dallas on Tuesday night. Their job is to contain any potential spread of the virus by working with local health officials to document whether the patient had contact with other people—who, where and when. How they’ll do this is less like the movie Outbreak and more of a labor-intensive process of interviews and monitoring.

The trail they will investigate starts Sept. 26, when a man came into Texas Health Presbyterian Hospital in Dallas for medical care. For two days, he had been feeling ill with fever and muscle aches—generally not concerning, which is why he was sent home. Two days later, he was worse, and was brought back to the hospital by ambulance.

It wasn’t immediately clear if doctors had asked the patient the critical question they should be asking all people who seek medical care for fevers, which is whether he had recently been outside of the U.S., and whether he had traveled to any of the countries in West Africa—including Guinea, Liberia or Sierra Leone—now battling the worst Ebola outbreak in the disease’s history. A Texas health official clarified Wednesday that a nurse had indeed asked the patient if he’d been to Africa and that he said he had, but hospital staff never factored that into their initial treatment.

MORE: How U.S. Doctors Can Contain Ebola

It turned out he had. Four days before he began feeling sick, the patient had been in Liberia before flying to the U.S. This time, based on his symptoms and his travel history, the doctors admitted him into an isolated room and called the state health department and the CDC’s 24-hour hotline; officials recommended testing the patient’s blood for the Ebola virus.

It tested positive, and now health officials from national and local agencies are on the scene. Their job is to contain any potential spread of the virus by documenting who, where and when the patient had contacted other people who might have been exposed via the patient. Because Ebola is only transmitted by droplets—in urine, blood or other body fluids—and only contagious when patients become symptomatic, those at highest risk are people who would have had the closest and most direct contact with the patient. Those who are exposed would also have to have direct mucous contact with infected fluids, such as via the eyes, nasal passages, or through a cut in the skin. So the passengers on the patient’s flights from Liberia to the U.S., for example, aren’t considered at high risk of exposure since he was not experiencing symptoms then.

MORE: Ebola in the United States: What You Need to Know

But the emergency medical personnel who brought the patient to Texas Health Presbyterian in the ambulance might be. They, and the man’s close family members, are being monitored for the virus’ longest incubation period—21 days—for any symptoms of Ebola, such as fever, nausea, vomiting or muscle weakness. If they don’t show any symptoms after that time, they’re likely in the clear.

Epidemiologists take a ring approach to tracing contacts of patients—starting with the circle of people with the most direct contact, such as family members or those who share close living arrangements. Each contact is asked about their own recent interactions with people, and this information is built into a contact tree of folks, not all of whom would be put on watch. Depending on how direct the contact with the patient was, even family members may not be quarantined but asked to refrain from traveling out of the city or country, for example, and avoiding public areas like movie theaters or shopping malls. A handful of children who were in the home with the patient are being monitored, local health officials said at a news conference on Wednesday, but they were allowed to attend school as usual.

MORE: Containing Ebola Is Extremely Labor Intensive, Former CDC Researcher Says

If anyone in the first circle of contacts develops symptoms, then doctors would step up their monitoring of the next ring of contacts, asking them to stay away from public gatherings for 21 days. This pattern continues until no one in a ring reports symptoms in the incubation period; that suggests they were not exposed and therefore don’t have the infection.

All of this, of course, depends on honest and accurate information from the patient and his contacts about where they have been and with whom—something that has been an issue in west Africa, where stigma against Ebola has led patients to flee health volunteers who are attempting to trace contacts, or fail to report people they have interacted with.

That shouldn’t be a problem here, CDC director Tom Frieden said. “We have identified all the people who could have had contact with the patient while he was infectious,” he said during a news conference. “We are stopping it in its tracks in this country. There is no doubt in my mind that we will stop it here.”

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