DALLAS - His week began thousands of miles away with a frantic bid to save a life.

It was Monday, Sept. 15, and Ebola, a terrifying disease, was ravaging West Africa, filling morgues and hospitals to capacity. In Monrovia, Liberia, the virus was about to claim one more person.

Marthalene Williams, seven months pregnant, had been diagnosed with low blood pressure when she was brought to a clinic, desperately ill.

Soon after coming home, she began convulsing. Thomas Eric Duncan, assisted by her family and others, lifted his neighbor into a taxi that rushed to a hospital maternity ward, where she was turned away. The 19-year-old woman returned to her house, where she died hours later.

That Friday, Sept. 19, Duncan arrived at Roberts International Airport in the capital of Monrovia.

He was about to embark on a three-leg journey, traveling from Africa, through Europe and into the United States. He would travel more than 8,000 miles before arriving at Dallas/Fort Worth International Airport in the early evening of Sept. 20.

His temperature, taken before he boarded the plane in Monrovia as part of precautionary government measures, had been below normal. But when he walked out into the steamy Texas night, he carried with him one of the deadliest diseases known to medicine.

Ten days later, he'd become the first person diagnosed in America with Ebola.

The same day that neighbors say Duncan carried his dying neighbor back into her home, the U.S. was calling for an emergency meeting of the U.N. Security Council to address the growing Ebola crisis.

The worst Ebola outbreak in history has swept through Liberia, Sierra Leone and Guinea, and has stretched into Nigeria and Senegal. Nearly 7,500 people are believed to have been sickened by the disease and more than 3,400 have died, according to the World Health Organization.

Liberia has been hardest hit, with more than 3,800 cases and slightly more than 2,000 deaths. But even those ghastly numbers likely underestimate the scope of the disaster and the true toll may never be known. The World Health Organization has noted that in the notoriously overcrowded slum of West Point, in the capital, bodies are just tossed into the river.

Liberia is woefully lacking beds in isolation units needed to care for people. Doctors Without Borders has described the heartbreaking act of turning away people who seek treatment at their centers in Monrovia.

The horrifying impact of Ebola can be seen and heard throughout Liberia's capital, from corpses on the street, men pushing the sick in wheelbarrows and the constant wail of ambulances. Even a public service phone message warns "Ebola is real" before a call comes through.

At the airport, nurses wearing white lab coats, face masks and gloves take the temperatures of departing passengers. There are giant dispensers with chlorinated water and buckets for hand-washing.

When Duncan arrived Sept. 19, his temperature was taken and recorded on a passenger screening form. It was 97.3.

Citing the Ebola outbreak, the form notes: "We need your help to prevent the spread of this disease."

Ebola is transmitted through direct contact with saliva, sweat and blood. It is not contagious until the symptoms begin.

The form asks travelers if they have any of 10 listed symptoms - among them, fever, vomiting, diarrhea, stomach pain and fatigue. Duncan answered "no" to all.

He also was asked if he'd taken care of an Ebola patient or touched the body of anyone who'd died in an Ebola-stricken area in the last 21 days - the incubation period. He answered "no" to both questions as well.

It's unclear if Duncan knew he may have been exposed to Ebola when he boarded his plane. While he had close contact days before with the pregnant woman, who neighbors now believe died from Ebola, she was never tested. It was initially suspected she had died of complications from her pregnancy.

On Sept. 25, Duncan was feeling sick enough that he went to the emergency room at Texas Health Presbyterian Hospital. He was reported to have a fever, headache and abdominal pain, but no diarrhea or vomiting. The hospital said he told them he'd recently arrived from West Africa, but that he denied having been around anyone sick. He was released.

By Sunday morning, Duncan's condition had worsened, and he is listed in critical condition at Texas Health Presbyterian Hospital in Dallas.