– Neighbors whisper that she is pregnant, a disgrace for a young, unmarried woman. The rumors mortify her.

Florence Ndimubakunzi is not pregnant. Her heart is failing. It pumps so poorly that blood backs up in her veins, bloating her liver and spleen, and filling her abdomen with fluid. She is only 18.

For millions like her in poorer parts of Africa, Asia and other regions, this devastating heart disease began insidiously. During childhood, they contracted strep throat — an infection caused by streptococcal bacteria.

In poor countries, strep throat often goes undiagnosed and can become a long, slow death sentence. It’s a public health disaster caused by a preventable disease that has been largely wiped out in the U.S. and Western Europe. Without treatment, it can lead to rheumatic fever and rheumatic heart disease, in which the immune system attacks the heart valves, which must open and shut properly 100,000 times a day for the heart to work normally. As the valves deteriorate, the heart gradually wears out. Many die before age 30.

Earlier this year, hoping to beat the odds, Florence and her mother consulted doctors from a humanitarian group, Team Heart, that flies in from the U.S. and Canada once a year to perform lifesaving valve-replacement surgery.

About 100 people showed up to be screened. The team could operate on only 16.

Lying on an examining table, Florence looked impossibly fragile. She had wasted away to 78 pounds; five were fluid.

Dr. Pat Come, a Harvard cardiologist, finally said, “She has significant disease of two valves. But the operative mortality is likely too high.”

If rheumatic fever is detected early, long-term treatment with penicillin can prevent valve damage. But many cases are already advanced.

“Unfortunately, the entry point is heart failure,” said Dr. Joseph Mucumbitsi, a pediatric cardiologist at the King Faisal Hospital in Kigali, and a consultant to Team Heart. “We have many rheumatic heart disease patients below 17. We have some as young as 5.”

He estimated that there might be as many as 20,000 people who need surgery. Rwanda has only five cardiologists and no heart surgeons or hospitals equipped to perform heart surgery — for a population of 12 million.

Since 2008, Team Heart has been traveling to Rwanda. The group was founded by Cecilia Patton-Bolman, an intensive-care nurse who had seen a ward full of teenagers dying from rheumatic heart disease when she visited the country in 2006, and her husband, Dr. R. Morton Bolman, who was then the chief of cardiac surgery at Brigham and Women’s Hospital.

Once a year, 40 to 60 volunteers fly to Kigali: heart surgeons, cardiologists, nurses, anesthesiologists, experts in cardiac ultrasound, biomedical technicians, pharmacists, support staff and perfusionists. An article in a medical journal earlier this year, based on the first 149 cases, reported a survival rate of 95 percent in the first month after surgery.

The Bolmans said it was always their intention to also train Rwandan doctors and nurses, and ultimately to build a cardiac hospital. “We envision putting ourselves out of business,” Patton-Bolman said.

Bolman estimated that it would cost $10 million to build a hospital and $10 million a year to run it. Rwanda’s minister of health, Dr. Diane Gashumba, said rheumatic heart disease was a real concern of the government. “We definitely need this center.”

The team has lined up prospective donors. But despite years of discussion, the government has not been able to commit to paying for patient care.