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Here's how you can (and can't) get Ebola

Now that New York City has announced its first-ever Ebola patient — a doctor who recently returned from Guinea, where he was fighting the virus —  confusion about how one gets Ebola has surfaced again. Dr. Craig Spencer, 33, took a three-mile run through the city, went bowling, and rode the subway with the Ebolavirus incubating in his body — setting off worry about contagion through bowling balls and subway cars.

But the facts about Ebola should put your mind at ease. In Spencer's case, he wouldn't have been shedding enough virus while he moved through the city to infect anyone because he only started showing symptoms Thursday morning, and was promptly quarantined. To understand why New Yorkers are most probably safe, here's a more concrete guide on how the virus can move from one person to another.

How you can get Ebola

1) You can get the virus if you have "direct contact" with a range of bodily fluids from a sick person, including blood, saliva, breast milk, stool, sweat, semen, tears, vomit, and urine. "Direct contact" means these fluids need to get into your broken skin (such as a wound) or touch your mucous membranes (mouth, nose, eyes, vagina).

2) So you can get Ebola by kissing or sharing food with someone who is infectious.

3) Mothers with Ebola can give the disease to their babies. Ebola spreads through breastfeeding — even after recovery from the disease. As one study put it, "It seems prudent to advise breastfeeding mothers who survive (Ebola) to avoid breastfeeding for at least some weeks after recovery and to provide them with alternative means of feeding their infants."

4) You can get Ebola through sex with an Ebola patient. The virus has been able to live in semen up to 82 days after a patient became symptomatic, which means sexual transmission — even with someone who has survived the disease for months — is possible.

5) You can get the virus by eating wild animals infected with Ebola or coming into contact with their bodily fluids. The fruit bat is believed to be the animal reservoir for Ebola, and when it's prepared for a meal or eaten raw, people get sick.

So you can get the virus through exposure to bat secretions. However, if you cook a bat infected with Ebola and then eat it, you won't get sick because the virus dies during cooking.

6) You can get Ebola through contact with an infected surface. Though Ebola is easily killed with disinfectants like bleach, if it isn't caught, it can live outside the body on, say, a doorknob or counter top, for several hours. In body fluids, like blood, the virus can survive for several days. So you'd need to touch an infected surface, and then put your hands in your mouth and eyes. But there would need to be a lot of virus in those bodily fluids to make someone else sick, which means the person would have to be very far along in the infection — unlike New York City's Spencer.

This is why the funerals of Ebola victims are problematic. Someone who has died from the virus will have a very high viral load. Since the virus can live in bodily fluids on their body, if you participate in the ritual washing of an Ebola victim and then touch your hands to your face, you could get the virus.

funeral ebola

A burial team from the Liberian Ministry of Health unloads the bodies of Ebola victims onto a funeral pyre in Marshall, Liberia. (Photo by John Moore/Getty Images News)

7) You could also get the virus by working in a biosafety-level-4 lab that studies Ebola, touching lab specimens, and then putting your contaminated hands in your mouth, eyes or a cut.

8) You can get Ebola by being pricked with a needle or syringe that has been contaminated with the virus. This has been a source of transmission for health workers, but unless you're sharing needles with Ebola victims, this isn't likely.

How you can't get Ebola

1) You can't get Ebola from someone who is not already sick. The virus only turns up in people's bodily fluids after a person starts to feel ill, and only then can they spread it to another person.

Again, this is why health officials say they are not worried about the people who were potentially exposed to Spencer's bowling balls or subway seat. At the time he was out and about, he was asymptomatic and therefore not a risk to those around him.

2) So you can't get Ebola from just sitting next to an asymptomatic, or even mildly symptomatic person on, say, a plane or subway. As one of the Ebola discoverers, Peter Piot, said, "I wouldn't be worried to sit next to someone with Ebola virus on the Tube as long as they don't vomit on you or something. This is an infection that requires very close contact."

3) You can't get Ebola from mosquitoes. The CDC says, "Only mammals (for example, humans, bats, monkeys and apes) have shown the ability to spread and become infected with Ebola virus."

4) You usually can't get Ebola through coughing or sneezing. The virus isn't airborne, thankfully, and experts expect that it will never become airborne. But, the Centers for Disease Control and Prevention
said, "If a symptomatic patient with Ebola coughs or sneezes on someone, and saliva or mucus come into contact with that person's eyes, nose or mouth, these fluids may transmit the disease." This happens rarely and usually only affects health workers or those caring for the sick.

The bottom line: Ebola is difficult to catch

As you'll probably have noted, Ebola isn't easy to transmit. The scenarios under which it spreads are very specific. And Ebola doesn't spread quickly, either. A mathematical epidemiologist who studies Ebola wrote in the Washington Post, "The good news is that Ebola has a lower reproductive rate than measles in the pre-vaccination days or the Spanish flu." He found that each Ebola case produces between 1.3 and 1.8 secondary cases. That means an Ebola victim usually only infects about one other person. Compare that with measles, which creates 17 secondary cases.

If you do the math, that means a single case in the US could lead to one or two others — which is exactly what we saw happen in Dallas. Hopefully New York learned the lessons of Dallas, and Ebola won't spread beyond Spencer. Because we have robust public health measures here, that's the most likely scenario here. Compare that to West Africa, which is now dealing with upwards of 9,000 cases in a completely broken health system. That's where experts say the worry about Ebola should be placed.