Source: Getty / Timothy A. Clary [1]

Dr. Craig Spencer tested positive for Ebola [2] on Thursday, becoming the first Ebola patient in NYC. He recently returned from Guinea, where he worked with Doctors Without Borders, and his steps are now being traced back to his return to NYC on Oct. 17. Meanwhile, it was reported on Friday that Nina Pham, a nurse who was diagnosed in Dallas, TX, will be released [3] from the hospital this week. News of US Ebola patients recently prompted Facebook founder Mark Zuckerburg to donate $25 million [4] to help fight Ebola. In a Facebook post, Zuckerburg noted that the epidemic is at "a critical turning point," saying he believes his grant "is the quickest way to empower the CDC." For a full breakdown on what's happening in the US and around the world, here are some frequently asked questions about Ebola, answered.

• Where did this start? Africa is currently experiencing a widespread outbreak of the virus. More than 4,000 people have died from Ebola [5], and almost 9,000 people have been diagnosed with the disease in countries including Liberia, Guinea, Nigeria, and Sierra Leone. On Oct. 14, the World Health Organization warned that there could be up to 10,000 new cases per week over the next two months.
• What's going on with the US Ebola patients? A man in Dallas named Thomas Duncan was the first person to be diagnosed with Ebola in the US. A week before his diagnosis, Duncan traveled from Liberia to America, and on Sept. 28, he was admitted to Texas Health Presbyterian Hospital, where he was isolated and eventually tested positive for Ebola. He was under intensive care, and on Oct. 8, he passed away. Twenty-six-year-old nurse Nina Pham contracted the virus at the hospital, and she's being released. A second Dallas hospital worker was also diagnosed, and on Oct. 24, Dr. Craig Spencer became the first Ebola patient in NYC.
• What's being done about air travel? Everyone who travels from Liberia, Guinea, Nigeria, and Sierra Leone to the US will have their temperatures taken when they arrive. In the case of Duncan, he didn't feel ill until days after landing back in the US, so it's likely that a standard screening test wouldn't have shown Ebola [6].
• How is Ebola transmitted? Is it contagious? Ebola is only contagious if the infected person is dealing with active symptoms. The CDC states that Ebola is spread through direct contact [7] with the blood or bodily fluids of an infected person, with infected animals, or with objects that have been contaminated, such as needles. It is not spread through the air, by water, or generally through food. That said, the virus has spread in Africa when people handled wild animals hunted for food and, in some cases, came into contact with infected bats.
• How is Ebola treated? There's no FDA-approved vaccine for the virus, and Ebola symptoms are treated [8] as they come up. A patient's recovery depends on the strength of his or her immune system, but general treatment involves an IV to bring more fluids and electrolytes into the body, plus the treatment of other infections that may arise.
• What is the CDC doing about this? You can follow CDC Emergency on Twitter [9] for live updates on the US case and its treatment.