Using old-fashioned detective work, public health workers in Mali, one of the world’s poorest nations, working with the U.S. Centers for Disease Control and Prevention and the World Health Organization, tracked and quarantined 108 people in two cities and a few roadside towns who may have had contact with a 2-year-old girl from Guinea who died of Ebola on Oct. 24.

There was even a car chase: The last bus the family traveled on during a 700-mile journey from Guinea was stopped on a rural highway, emptied out and disinfected.

The 21-day quarantine period since the little girl’s death on Oct. 24 is almost over, with 41 of the 108 Malians in quarantine due to be released Tuesday, and the remainder by Friday. Since none are showing symptoms, health officials are allowing themselves to hope that their quick response has kept Mali’s first outbreak to a single case.

If so, Mali will join Senegal and Nigeria in having proved yet again that rapid reactions can stop Ebola. In contrast, the initial outbreak in Guinea festered unaddressed for months before it exploded.

"I’m actually feeling very good right now," Dr. Rana Hajjeh, who led the CDC advisory team, said Friday. "We feel reassured that most of the danger is over."

The case also illustrates how even people in close contact with victims do not necessarily get the disease, which spreads when infectious fluids get into an open cut, or a nose, eye or mouth.

Remarkably, no one who touched the girl, Fanta Conde, in Mali is yet sick. Not the woman she called grandmother, her 5-year-old sister or her uncle, who all spent three days traveling with her from Beyla, Guinea. Not Dr. Abdouramane Koungoulba, the pediatrician who first examined her on Oct. 21, nor two traditional healers who saw her earlier, nor any of a dozen other doctors or nurses who gave her a transfusion and intravenous hydration and cleaned up her vomit and diarrhea in the 48 hours before she died.

Nor, apparently, are any of the dozens of bus passengers, taxi drivers, family friends or other contacts she had while traveling.

The episode also drew attention to an unusual decision by President Ibrahim Boubacar Keota: Unlike most West African countries, Mali has not closed its border with an Ebola-affected neighbor – in this case, Guinea.

That is partly for practical reasons. There are so many gravel roads crossing the long border that closing it is probably impossible.

Dr. Abdou Salam Gueye, a CDC investigator, explained that closing the border would violate an honored Malian principle of diatiguiya (pronounced JAH-tih-GEE), the belief that hospitality to friends and even strangers is obligatory. It extends back centuries, to the days when Mali was the core of a great West African empire, and travelers with introductions were welcomed like family.

Michel Sidibe, the Malian executive director of UNAIDS, the United Nations HIV-fighting agency, said diatiguiya is a Mandingo tradition.

"If I come to my diatiguiya’s house, he cannot close the door," Sidibe explained. "His home is my home. Even if I am sick, he must bring me in. And this has extrapolated into ‘I cannot close the border.’"

Mali’s harrowing brush with Ebola began last month with a woman’s selfless act: trying to rescue two young girls in her family from the disease. Aminata Gueye Tamboura, 45, fetched them from their ailing family in Guinea, the cradle of the epidemic, then took them aboard buses and taxis, back to her home in Kayes, in northwest Mali. (Tamboura, although called Fanta’s grandmother, is actually the second wife of Fanta’s grandfather in a polygamous marriage.)

Fanta had a 104-degree fever and an unstoppable nosebleed by the time she was hospitalized. Health officials feared she had seeded the virus all along the route, potentially turning Mali into the fourth nation engulfed by the disease.

The child’s family in Guinea did not believe the virus existed and rejected medical help, even as relatives began to die there, including Fanta’s father, said Dr. Ibrahima Soce Fall, leader of the WHO team in Mali. Fanta’s mother remained in Guinea with a 3-month-old baby because she had to observe 40 days of mourning for her husband, Koungoulba said.

Tamboura, the girls and an uncle left Beyla, a small city, on Oct. 18 in a 10-passenger "bush taxi," and crossed the border the next day. Some passengers said Fanta was given acetaminophen to lower her fever and avoid detection. Tamboura denied it.

During a three-hour layover in Bamako, Mali’s capital, the family took taxis to and from the compound of family friends, and rested there. That compound is now also quarantined with 25 people inside; the government delivers food and has posted guards to make sure no one leaves.

In Kayes, Tamboura took Fanta to two traditional healers, known as marabouts, and then to a neighbor, a former doctor, who urged her to go to Fousseyni Daou Hospital, which she did on Oct. 21.

Initially, Koungoulba said, she told him Fanta was a local child, so he did not suspect Ebola. He did wear gloves, but no other protection.

That evening, Tamboura’s sister admitted that Fanta was Guinean, so he ordered an Ebola test. But it took 24 hours for a car to arrive from Bamako and fetch the sample.

When it turned up positive on Oct. 23, Koungoulba kept asking himself: "Did I do everything I should? Did I touch her dirty diaper or the blood running from her nose?"

Hajjeh, who had just finished helping Mali devise a response plan in case the disease ever arrived, said she was at the airport when she heard the test results were positive.

"I canceled my flight and stayed," she said.

At the hospital, about a dozen staff members were quarantined, as were Fanta’s family and all 40 patients and their families, who sleep under trees on the dusty grounds to help care for the sick.

It was partly for their own protection, doctors said, since there had been angry reactions elsewhere in Mali to earlier suspected cases, which turned out to be false alarms.

Tensions rose when Fanta died the next day. By then, the government was making national broadcasts, looking for everyone who had ridden the buses.

They found many of them through old-fashioned sandal leather: Some passenger lists had cellphone numbers, but in Mali, a village might share one phone. The authorities estimate that they failed to find 39 passengers, but none who sat near the family.

Then Fanta’s 5-year-old sister developed a fever, but it turned out to be malaria, and curable.

Luckily, rumors that the disease did not exist, or that Westerners started it to sell drugs, got little traction in Mali. But in Guinea, such beliefs crippled the response to the epidemic for weeks.

Many Malians stopped shaking hands, opting to touch their hearts in the Muslim "salaam" or do the "WHO elbow bump."

"Some even do like the Dalai Lama," said Fall of the WHO, meaning they bowed with hands in a praying position. "They laugh when they do it, but at least they do it."

Hand-washing stations — often just a plastic teakettle of water with soap — are now required in buses. (While hand sanitizers are easier, some Muslims shun them because they contain alcohol, Hajjeh said.)

Some customs did not change: Friends continued sharing tea glasses and eating from common plates, even inside the hospital.

Senegal’s outbreak was one case with few suspected contacts. Nigeria’s was large — 21 cases in two major cities. But its response was powerful and efficient, said Samantha Bolton, a WHO spokeswoman. Nigeria turned the emergency operations center it created for polio over to its Ebola team, and health workers made 18,500 home visits to more than 900 contacts.

"In Nigeria, the government was very, very much in control," Bolton said. "That needs to happen in Mali. Here, the government could probably do with a few more people on each team."

The country recently appointed an Ebola coordinator, so it will be better prepared next time, if there is one.

© 2014 The New York Times Company