The two girls had nursed their mother as she died. They braided her hair until a truck came for the corpse. As Ebola leapt from house to house in the sprawling slum, it seemed inevitable that the girls, aged 12 and 13, would soon come down with the disease themselves. They would be the next links in an endless chain of transmission that was destroying New Kru Town, a suburb of Monrovia. And it was Bobby Pomney’s job to intervene.

Mr Pomney is a “contact tracer” for the Liberian government. When he arrived on a sweltering morning earlier this month, Mary Nyanford’s body was being driven away. Princess was screaming for her mother. Tears were running down Georgina’s cheeks.

“These girls need to be isolated,” said Mr Pomney, a slim, bald man, sweat beading on his forehead.

There may be only one way to halt the worst Ebola outbreak in history: find the disease’s victims, strictly quarantine them and monitor everyone with whom they interacted.

Contact tracing and enforcing quarantines in a place like New Kru Town is fraught with difficulties. Everything is shared: mattresses, toilets, food, the burden of caring for the ill. Mr Pomney, 43, was from a slum himself, and he knew the odds he would face as he kept watch over the two little girls.

New Kru Town is a maze of sheet-metal shanties built on a small peninsula, about a mile long and a half-mile wide, that juts into the Atlantic. Depending on who you ask, the population is 20,000 or 50,000. It’s a place with open sewers and swarms of mosquitoes that seems as if it was constructed to facilitate the spread of disease. It is an overwhelmingly difficult place to do contact tracing.

“I know this is my job,” Mr Pomney said later. “But I don’t think it works here.” The day after Ms Nyanford’s body was carried away, Mr Pomney returned with a clipboard and rain boots. He started writing down the names of people who had physical contact with her while she was sick.

In pictures: Ebola virus Show all 62 1 /62 In pictures: Ebola virus In pictures: Ebola virus Ebola virus A health worker from Sierra Leone's Red Cross Society Burial Team 7 carries the corpse of a child in Freetown In pictures: Ebola virus Ebola virus A health workers from the Sierra Leone's Red Cross Society Burial Team 7 is sprayed with desinfectant after removing a corpse from a house in Freetown In pictures: Ebola virus Ebola virus Health workers from Sierra Leone's Red Cross Society Burial Team 7 prepare to remove a body from a house in Freetown AFP In pictures: Ebola virus Ebola virus Health workers from the Sierra Leone's Red Cross Society Burial Team 7 place a body in a grave at King Tom cemetary in Freetown In pictures: Ebola virus Ebola virus Mustapha Rogers of the Red Cross talks as health workers from the Sierra Leone's Red Cross Society Burial Team 7 remove a corpse from a house in Freetown In pictures: Ebola virus Ebola virus A citizen from Mali arrives at a hospital in Murcia city, south-eastern Spain. The protocol for a possible case of Ebola has been activated as the man, who arrived from Mali to Jumilla town in Murcia province five days ago, presents clinical symptoms of high fever and vomiting EPA In pictures: Ebola virus Ebola virus Kenyan medical workers show how to handle an infected Ebola patient on a portable negative pressure bed at the Kenyatta national hospital in Nairobi Getty Images In pictures: Ebola virus Ebola virus A health worker sprays disinfectant onto a college in Monrovia, Liberia AP In pictures: Ebola virus Ebola virus A burial team in protective gear bury the body of a woman suspected to have died from Ebola virus in Monrovia, Liberia In pictures: Ebola virus Ebola virus Healthcare workers in protective gear work at an Ebola treatment center in the west of Freetown, Sierra Leone AP Photo/Michael Duff In pictures: Ebola virus Ebola virus A healthcare worker in protective gear is sprayed with disinfectant after working in an Ebola treatment center in the west of Freetown, Sierra Leone In pictures: Ebola virus Ebola virus A member of the NGO U Fondation leaves a house after visiting quarantined family members suffering from the Ebola virus in Monrovia In pictures: Ebola virus Ebola virus An Ebola sign placed infront of a home in West Point slum area of Monrovia, Liberia In pictures: Ebola virus Ebola virus A Liberian man carries his sick brother suspected of having Ebola after being delayed admission to the Island Clinic Ebola Treatment Unit due to a lack of beds at the clinic on the outskirts of Monrovia, Liberia In pictures: Ebola virus Ebola virus Health workers remove the body a woman who died from the Ebola virus in the Aberdeen district of Freetown, Sierra Leone In pictures: Ebola virus Ebola virus A health worker fixes another health worker's protective suit in the Aberdeen district of Freetown, Sierra Leone In pictures: Ebola virus Ebola virus Health workers spray themselves with chlorine disinfectants after removing the body a woman who died of Ebola virus in the Aberdeen district of Freetown, Sierra Leone In pictures: Ebola virus Ebola virus A woman crawls towards the body of her sister as Ebola burial team members take her sister Mekie Nagbe (28) for cremation in Monrovia, Liberia In pictures: Ebola virus Ebola virus Sophia Doe sits with her grandchildren Beauty Mandi, 9 months (L) and Arthuneh Qunoh, 9, (R), while watching the arrival an Ebola burial team to take away the body of her daughter Mekie Nagbe, 28, for cremation in Monrovia, Liberia In pictures: Ebola virus Ebola virus Varney Jonson (46) grieves as an Ebola burial team takes away the body of his wife Nama Fambule for cremation in Monrovia, Liberia In pictures: Ebola virus Ebola virus Family members grieve as Ebola burial team members prepare to remove the body of Nama Fambule for cremation in Monrovia, Liberia In pictures: Ebola virus Ebola virus A Liberian burial squad carry the body of an Ebola victim in Marshall, Margini county, Liberia In pictures: Ebola virus Ebola virus An Ebola burial team dresses in protective clothing before collecting the body of a woman (54) from her home in the New Kru Town suburb of Monrovia, Liberia In pictures: Ebola virus Ebola virus An Ebola burial team carries the body of a woman (54) through the New Kru Town suburb of Monrovia, Liberia In pictures: Ebola virus Ebola virus An Ebola burial team dresses in protective clothing before collecting the body of a woman (54) from her home in the New Kru Town suburb of Monrovia, Liberia In pictures: Ebola virus Ebola virus Health workers in protective gear carry the body of a woman suspected to have died from Ebola virus, from a house in New Kru Town at the outskirt of Monrovia, Liberia In pictures: Ebola virus Ebola virus Volunteers in protective suit bury the body of a person who died from Ebola in Waterloo, some 30 kilometers southeast of Freetown FLORIAN PLAUCHEUR/AFP/Getty Images In pictures: Ebola virus Ebola virus Nowa Paye (9) is taken to an ambulance after showing signs of the Ebola infection in the village of Freeman Reserve, about 30 miles north of Monrovia, Liberia In pictures: Ebola virus Ebola virus Medical staff members burn clothes belonging to patients suffering from Ebola, at the French medical NGO Medecins Sans Frontieres (MSF) in Monrovia PASCAL GUYOT/AFP/Getty Images In pictures: Ebola virus Ebola virus A medical staff member wearing a protective suit walks past the crematorium where victims of Ebola are burned in Monrovia In pictures: Ebola virus Ebola virus A Liberian burial team wearing protective clothing loads the body of a 60-year-old Ebola victim after retrieving him from his home Getty Images In pictures: Ebola virus Ebola virus Sick women rest while hoping to enter the new Doctors Without Borders (MSF), Ebola treatment center near Monrovia, Liberia Getty Images In pictures: Ebola virus Ebola virus Hanah Siafa walks in the rain with her children Josephine, 10, and Elija, six, while waiting to enter the new Doctors Without Borders (MSF), Ebola treatment center in Monrovia, Liberia Getty Images In pictures: Ebola virus Ebola virus UNICEF health workers walk through the streets, going house to house to speak about Ebola prevention in New Kru Town, Liberia. The virus has killed more than 1,000 people in four African countries Getty Images In pictures: Ebola virus Ebola virus Local residents watch as public health advocates stage an Ebola awareness and prevention event in Monrovia, Liberia Getty Images In pictures: Ebola virus Ebola virus Public health advocates stage an Ebola awareness and prevention event in Monrovia, Liberia. The Liberian government and international groups are trying to convince residents of the danger and are urging people to wash their hands to help prevent the spread of the epidemic Getty Images In pictures: Ebola virus Ebola virus Hanah Siafa lies with her children Josephine, 10, and Elija, six, while hoping to enter the new Doctors Without Borders (MSF), Ebola treatment center Getty Images In pictures: Ebola virus Ebola virus A health worker examines patients for Ebola inside a screening tent, at the Kenema Government Hospital AP In pictures: Ebola virus Ebola virus A health worker cleans his hands with chlorinated water before entering an Ebola screening tent at the Kenema Government Hospital, about 86 miles from Sierra Leone’s capital Freetown AP In pictures: Ebola virus Ebola virus Aid workers and doctors transfer Miguel Pajares, a Spanish priest who was infected with the Ebola virus while working in Liberia, from a plane to an ambulance as he leaves the Torrejon de Ardoz military airbase, near Madrid, Spain AP Photo/Spanish Defense Ministry In pictures: Ebola virus Ebola virus A Liberian money exchanger washes hands between customers as a precaution to prevent infection with the deadly Ebola virus while conducting business in downtown Monrovia, Liberia EPA In pictures: Ebola virus Ebola virus A Liberian health worker sprays disinfectant on a drivers boots to stop the spread of the deadly Ebola virus at the Christian charity Samaritan Purse head offices in Monrovia, Liberia. Over 660 people have died of Ebola in West Africa in 2014 making it the world's deadliest outbreak to date according to statistics from the World Health Organisation EPA In pictures: Ebola virus Ebola virus A Liberian taxi driver wears protective gloves as a precaution to prevent infection with the deadly Ebola virus whilst driving in downtown Monrovia, Liberia. Many Liberians have taken to wearing gloves and washing hands after every interaction in an attempt to curb the spread of the deadly virus EPA In pictures: Ebola virus Ebola virus A Liberian money exchanger wears protective gloves as a precaution to prevent infection with the deadly Ebola virus while transacting business with customers in downtown Monrovia, Liberia EPA In pictures: Ebola virus Ebola virus A woman from Liberia takes food to a sick relative in the Ebola isolation unit at the ELWA Hospital where US doctor Kent Bradley is being quarantined having contracted the Ebola virus. Over 660 people have died of Ebola in West Africa in 2014 making it the world's deadliest outbreak to date according to statistics from the World Health Organisation EPA In pictures: Ebola virus Ebola virus The disease has now spread to Liberia and, for the first time, Sierra Leone and Nigeria, killing at least 672 people in 1,201 cases, according to the World Health Organisation’s latest figures AP In pictures: Ebola virus Ebola virus Health specialists prepare for work in an isolation ward for patients at the Medecins Sans Frontieres facility in southern Guinea AFP/Getty Images In pictures: Ebola virus Ebola virus A Liberian street vendor wears protective gloves as a precaution to prevent infection with the deadly Ebola virus while transacting business with customers in downtown Monrovia, Liberia EPA In pictures: Ebola virus Ebola virus A nurse from Liberia sprays preventives to disinfect the waiting area for visitors at the ELWA Hospital where a US doctor Kent Bradley is being quarantined in the hospitals isolation unit having contracted the Ebola virus, Monrovia, Liberia EPA In pictures: Ebola virus Ebola virus Staff of the 'Doctors without Borders' ('Medecin sans frontieres') medical aid organisation carry the body of a person killed by the virus In pictures: Ebola virus Ebola virus A Liberia man (right) talks to a nurse (left) about the health of his relative who is in the isolation unit of the ELWA Hospital where a US doctor Kent Bradley is being quarantined having contracted the Ebola virus, Monrovia, Liberia EPA In pictures: Ebola virus Ebola virus A nurse from Liberia walks to spray preventives to disinfect the waiting area for visitors at the ELWA Hospital where a US doctor Kent Bradley is being quarantined in the hospitals isolation unit having contracted the Ebola virus EPA In pictures: Ebola virus Ebola virus Staff of the Christian charity Samaritan's Purse put on protective gear in the ELWA hospital in the Liberian capital Monrovia AFP In pictures: Ebola virus Ebola virus Lagos State Health Commissioner Jide Idris, speaks, during a news conference in Lagos, Nigeria. No one knows for sure just how many people Patrick Sawyer came into contact with the day he boarded a flight in Liberia, had a stopover in Ghana, changed planes in Togo, and then arrived in Nigeria, where authorities say he died days later from Ebola AP Photo/Sunday Alamba In pictures: Ebola virus Ebola virus Staff of the Christian charity Samaritan's Purse put on protective gear in the ELWA hospital in the Liberian capital Monrovia. An American doctor battling West Africa's Ebola epidemic has himself fallen sick with the disease in Liberia, Samaritan's Purse said AP In pictures: Ebola virus Ebola virus Protective gear including boots, gloves, masks and suits, drying after being used in a treatment room in the ELWA hospital in the Liberian capital Monrovia AFP In pictures: Ebola virus Ebola virus A Liberian man holding a Civet being sold on a roadside as bush meat in Lofa County. Bush meat is one of the major carriers of the Ebola virus. The Liberian government and International partners have warned people to not eat it. The World Health Organisation (WHO) reported that a total of 888 Ebola cases including 539 deaths have been recorded in West Africa since February AFP In pictures: Ebola virus Ebola virus People unload protection and healthcare material at Conakry's airport, to help fight the spread of the Ebola virus and treat people who have been already infected AFP/Getty Images In pictures: Ebola virus Ebola virus Body of evidence: health workers transport a casket of a nun whose death resulted from an Ebola infection in Zaire in 1995 Getty In pictures: Ebola virus Ebola virus Peter Piot in Yambuku, northern Congo (then Zaire), in 1976, where he was part of the original team to discover the Ebola virus J Breman In pictures: Ebola virus Ebola virus A member of Doctors Without Borders helps to unload protection and healthcare materials in Guinea Getty In pictures: Ebola virus Ebola virus Doctors in protective gear work inside the Medecins Sans Frontieres isolation ward as Guinea faced the worst ever outbreak of the Ebola virus Getty Images

Some people he visited wouldn’t give their names. Others denied that they had been around Ms Nyanford, apparently to avoid being ordered into the 21-day quarantine, even though it was not enforced. “You all want to quarantine us, but how are we going to eat?” asked Cleo Tobar.

Ebola had been raging across Liberia for seven months. In the country’s infected areas, quarantine means not socialising with other people. No sharing food. No sharing a bathroom. Ebola is spread through the bodily fluids of highly infected people.

Scientists use formulas to map Ebola’s transmission vectors and its exponential infection rate. But New Kru Town is a place where you can watch the virus’s web grow outward in real time.

Every day that Mr Pomney returned, he was approached by someone reporting a new case: a corpse that had been left on a mattress for three days until it started to decay; the body of an 11-month-old boy; a young man with a high fever who sat zombie-like in front of his house. “This whole area is infected,” he said.

Mr Pomney was left with hardly any contacts to trace, except for the two little girls whom everyone watched, waiting for symptoms to emerge.

Days later, Mr Pomney sighed and walked to a home pointed out by another slum resident. Another member of the contact tracing team, John Shagbeh, joined him. When they got to the house, a few yards from where Ms Nyanford had died, a man in his early 20s was sitting, staring blankly.

“This guy needs to go to the hospital,” Mr Shagbeh said. “We went to the doctor. He said it’s yellow fever,” the man’s mother said.

The contact tracers didn’t believe her. Many people in New Kru Town are desperate to avoid Ebola treatment centres, which they see as dangerous.

“If you don’t go to the hospital, we will call the police on you,” Mr Shagbeh shouted. “You need to accept that this man is infected.”

Red Cross members carry the body of an Ebola victim in Monrovia, Liberia, earlier this month (Anadolu Agency/Getty) (Anadolu Agency/Getty Images)

In Nigeria, where there were 20 confirmed or probable cases of Ebola in July, tracers created a list of 894 contacts of the patients, and isolated and monitored them. Health workers conducted 18,500 face-to-face visits.

Last week, the country was declared Ebola-free.

But in Liberia, where more than 4,600 people have been diagnosed with the disease since March, improvised contact-tracing teams were formed only after Ebola had spread widely.

There could be tens of thousands of contacts scattered across slums like New Kru Town. The country’s public health system was almost nonexistent even before Ebola.

In the United States, many contact tracers have advanced degrees in public health. In Liberia, they are former students or shopkeepers or security guards. Until June, Mr Pomney sold stationery.

Liberia’s contact tracers are supposed to make daily checks on victims’ friends, relatives and neighbours, beginning as soon as the cases are identified. But in New Kru Town, the tracers said, it typically takes about 10 days before the process even begins. By that time, more people have typically developed symptoms.

“You can’t quarantine people here. We’re all intertwined,” said Aloysius Nimely, the pastor of Garden Street Temple Bible Wheel Church.

A health worker sprays disinfectant onto a college in Monrovia, Liberia (AP)

As families attended church services, Mr Pomney was running between houses. In three hours, he had heard about three new bodies. His job is not to remove the dead, but he was the only representative of the Liberian government in the slum, and he decided he had to do something.

He called the body-collection team. He waited with the families. He took out his clipboard and tried to diagram the web of physical contacts orbiting the deceased. Each time, he got a few names, and then he gave up. The circles were too wide. There were too many people who didn’t want to give their names or didn’t want to admit that they had had contact with the dead.

Exactly one week after Ms Nyanford’s body was driven away, Mr Pomney walked by Princess and Georgina, who were sitting in a circle with relatives.

“It’s only a matter of time,” he said. “One day, they’re going to get it.”