Three years ago, Jesús Tilano went to a hospital in a thickly forested valley in Colombia with large open lesions on his nose, right arm, and left hand. He was diagnosed with leishmaniasis, a parasitic disease that is spread in the bite of a female sand fly and which plagues poor people who work in fields or forests across developing countries. He was prescribed a drug that required three injections a day for 20 days, each one agonizingly painful. Mr. Tilano, 85, had to make repeated expensive bus trips to town to get them. Then his kidneys started to fail, which is a common side effect of the drug, as are heart failure and liver damage. “The cure was worse than what I had before,” Mr. Tilano said.

Leishmaniasis is a terrible disease, with terrible treatments that have hardly changed in a century. The drug Mr. Tilano took was first given 70 years ago. All the treatments are some combination of painful, toxic, expensive, or challenging to administer, requiring an inpatient hospital stay or daily visits for a month.

Among the so-called “neglected tropical diseases,” many experts believe leishmaniasis is in a class of its own in terms of the lack of progress, in the 120 years since it was first identified, to help the two million people who contract it each year.

Now, finally, that is starting to change: When Mr. Tilano’s grandson Andrés Tilano, 14, contracted leishmaniasis last year, he was treated in a clinic in Medellín, with an experimental therapy that cured his infection in days.

The treatment he received is one of several being developed by the Program for the Study and Control of Tropical Diseases, known as PECET, a small research institute based at the University of Antioquia in Medellín. In its effort to hunt for new treatments for leishmaniasis, the program has partnered with the Drugs for Neglected Diseases Initiative, or DNDi, a nonprofit research and development organization based in Geneva.

All of the experimental treatments the researchers are evaluating are far less toxic, onerous, or expensive than what exists now. But a big hurdle still stands in the way of getting them to the millions of people who need them. None of the new treatments have been tested in a large-scale trial, or approved by Colombia’s drug regulator, or adopted into the national treatment guidelines.

When a drug is made by a pharmaceutical company, the firm will shepherd it through the expensive and time-consuming regulatory process. But there is no money to be made on a drug for a condition that overwhelmingly affects the poor, and academic or public health institutes rarely have the resources to push a drug through to the end of the process.

Marcela Vieira, a Brazilian intellectual property lawyer with an expertise in drug development and access, explained that the global drug development system has long favored private sector firms that can bankroll experiments and diseases that afflict people with money to pay for treatments. However, new research on diseases such as leishmaniasis is increasingly coming from public sector and academic institutions in middle-income countries.

The Covid-19 pandemic led to new investment into building drug development and production capacity for lower- and middle-income countries, said Dr. Juliana Quintero, an expert in leishmaniasis and researcher at PECET.

The program’s research labs sit six floors up in a bulky brick building at the University of Antioquia in Medellín. On the ground floor, Dr. Quintero sees patients who arrive on buses from rural towns. She knows that few can afford to stay in the city for a month of injections; she wants a treatment she can send home with them, ideally one they can take by mouth. Because funds for drug development for leishmaniasis are so scarce, she hopes for something that will work for every one of the 22 parasites in the family that cause variations of the disease in tropical countries around the world.

Dr. Quintero has taken inspiration from Indigenous people in the region, and they are testing a drug that is a gel applied to lesions, which is derived from a plant Indigenous people use to fight the parasite. The experimental treatment that cured Andrés Tilano is called thermotherapy, and in Dr. Quintero’s clinic, she used a hand-held device that emitted heat at 50 degrees Celsius, or 122 degrees Fahrenheit, over top of the lesion, killing the parasite deep inside.

Today, Dr. Quintero prescribes two treatments her institute has developed and supplies them to patients under a so-called compassionate use model, since they have not yet been approved or registered by the Colombian government.

Mr. Tilano and his grandson had cutaneous leishmaniasis, which is the least severe form of the disease. It can progress to other more severe forms of the disease if left untreated. The number of deaths from the disease has dropped significantly in the past few years, mainly because of progress in finding and treating leishmaniasis in India, where it is known as kala-azar.

Because the existing treatments are so onerous and hard to get, Dr. Quintero said, few patients complete the course. That creates newly drug-resistant parasites which are then transmitted to others in their community. When Dr. Quintero went to visit Mr. Tilano at home not long ago, she met his daughter and granddaughter, who had the large circular scars of lesions that had finally healed.