One summer’s morning Paniya Sardar noticed a strange mark on her leg. It was the size of her palm, light in colour and felt numb to touch. She had no idea what had caused it.

The family took Paniya, then 14, to a private clinic near their home on the outskirts of Biratnagar, a city in southern Nepal, where they were sold lotions and pills and told not to worry. Three months later, a deep wound appeared on her foot. “This particular blister was pretty big and wouldn’t heal,” her father, Sita Sardar, says through an interpreter. Six months later, it was still there.

Paniya was eventually diagnosed at a local hospital with leprosy, one of the oldest recorded diseases. “[Doctors] were speaking very hard words and talking loudly,” she remembers. “[I] thought, ‘Why has this happened to me?’”

The World Health Organization declared that leprosy had been eliminated as a public health problem globally in 2000, after a fall in international prevalence rates. Nine years later, Nepal’s government reported it had reached targets to eliminate the disease as a public health problem nationally. But critics say such claims were misleading. They insist these claims led to the defunding of leprosy research and caused health departments to wind down services designed to spot patients such as Paniya.

Paniya Sardar, 17, had surgery to regain the full use of her left hand after contracting leprosy at the age of 14. She will soon start physiotherapy to re-teach her brain how to control her fingers. Photograph: Sailendra Kharel/The Guardian

It’s feared that thousands of cases are going undiagnosed across Nepal – and that millions are missing from statistics globally.

“People have misunderstood, [and believe] that somehow the disease was eliminated when in fact new cases are still occurring,” says Professor W Cairns Smith, emeritus professor of public health at the University of Aberdeen.

“The harder you look the more you find,” he says. “We’re not really looking hard enough.”

Leprosy, caused by bacteria called Mycobacterium leprae, is curable, and disability can be prevented with early treatment. But the disease is poorly understood and signs are often missed. Despite its reputation as a very contagious disease, 95% of the world’s population are immune. It’s not known why certain people are more vulnerable than others, and the mode of transmission – it’s thought to be passed on through nasal droplets – is still not fully understood. The tools for diagnosing leprosy are also limited. A skin smear can be taken from behind a patient’s ear, but this doesn’t identify all types of leprosy.

Doctors and nurses instead rely on symptoms such as skin lesions to make a diagnosis, but these can be mistaken for other conditions, says Dr Mahesh Shah, senior consultant dermatologist at Patan clinic, run by the Leprosy Mission, in Lalitpur. “Depending on the leprosy, it takes a long [time] to have proper clinical signs and symptoms. It may be five years, 10 years. From the patient side also it is difficult to recognise the problem.”

Kharka Bahadur Chettri, 75, sits with his wife Sabitri Chettri, 73, outside their room in the Khokana leprosy colony. They met at Khokana and have been married for 47 years. Photograph: Sailendra Kharel/The Guardian

By the time Paniya was correctly diagnosed with leprosy, she had experienced irreversible nerve damage that left her hands with little sensation. This eventually caused her hands to claw – a common symptom of leprosy that not only means she has limited use of her hand, but also that the disease is almost impossible to hide.

Paniya’s experience is the kind of case that the WHO wants to prevent. It calls for patients to be identified earlier, and set a target for zero disabilities among new paediatric patients by 2020. This target is partly aspirational, says Smith: “It focuses the mind to say: this is not acceptable.”

In Nepal, the Leprosy Mission carries out preventative work among communities at risk. “If someone is diagnosed we go and screen family members, even the neighbours,” says Shovakhar Kandel, the charity’s country leader for Nepal.

Some families, such as Paniya’s, are also being offered a post-exposure treatment that can prevent them from developing leprosy. The therapy – known as leprosy post-exposure prophylaxis – is the first major breakthrough in leprosy since multi-drug therapy was introduced as a treatment in the 1980s.

Research suggests it is 50-60% effective in preventing the development of the disease over the following two years. But its success depends on health departments funding specialist workers to track families, work that ground to a halt in many countries after the global elimination target was reached in 2000 – when the prevalence rate was reported to have fallen to less than one case per 10,000 people.

Ajay Kumar Chaudhari, 35, sits with his seven-year-old son, Vivas, in their room in the Khokana leprosy colony, where about 350 people sufferers live. Chaudhari receives 1,500 rupees per month, roughly £10.40 Photograph: Sailendra Kharel/The Guardian

Today, Paniya, now 17, is sitting in a physiotherapy room of Anandaban hospital, a specialist facility near to Kathmandu, her arm cased in thick plaster of paris.

She has just undergone life-altering surgery to regain the full use of her left hand. This involves cutting slits into a tendon from her longest finger and attaching this to her other fingers. Through months of intensive physiotherapy at the hospital, run by the Leprosy Mission, she will slowly reteach her brain how to use her fingers again – a first step in rebuilding her life.

Nobody in Paniya’s family told the neighbours that she had leprosy. She begged her mother not to ask for a discount on local buses which, as a person affected by leprosy, she was entitled to receive. When multidrug therapy caused her skin to darken, the family told people that she had a skin condition. Eventually people started to guess.

Paniya Sardar’s family at their home in Rangeli, near to Biratnagar. Her father, Sita, work as a labourer and her mother, Sumitra, works as a cleaner in a local hospital. Photograph: Sailendra Kharel/The Guardian

Neighbours began to treat the family differently. “The disgust showed in their face,” says Sumitra Sardar, Paniya’s mother, who works as a cleaner. Before, she would go to watch television at her friends’ houses, but their parents stopped her from visiting.

During treatment, many patients – including Paniya – experience fever and inflammation of the skin. “Right after taking medication her face started changing, almost bending,” her father says. “She got more ill, to the point when she had never been ill like that before,” adds Sumitra. For a year, Paniya suffered weakness, fever, difficulty breathing, dry ulcers and nosebleeds.

When her mother went in to meet with a teacher about her condition, she found that Paniya’s name had been removed from the register. “The teacher said she is a big girl now, she doesn’t need to study,” says Sumitra. Paniya was 15.

Attitudes towards leprosy in Nepal have changed in recent decades: the belief that leprosy is a curse sent by God has faded, says Jaybind Kumar Yadav, secretary of the Nepal branch of Idea, the International Association for Integration, Dignity and Economic Advancement, a group run by people affected by leprosy.

Idea recently assisted a woman who had been cast out and spent more than two decades living in a cave. Such cases are less common today, says Yadav, though around 350 people continue to live at Khokana leprosy colony, first established as a place to quarantine people with the disease.

“Right now the message is they are segregated, and kept away from the community,” says Yadav. Rehabilitating people back in the community would send a signal that this is wrong.

Gyani Maya, 65, moved recently to Khokana. She has had leprosy since she was a child but didn’t receive treatment until she was an adult. At Khokana, Laxmi Khatri and her 14-year-old son Ishwor help to care for her. Photograph: Sailendra Kharel/The Guardian

At home, Paniya’s mother worries about the future, and wonders if the disease will prevent her daughter from earning or having a family. “Paniya is a daughter who needs to be married, [we] can’t take care of her forever.” Sumitra says. But she will need to be honest about her condition: discriminatory laws mean it is forbidden for a person to “deceptively marry or arrange marriage” with a person who is affected by leprosy.

The disease has already placed an enormous financial burden on the family. Her dad hopes she will be able to do tailoring work or open up a shop for cosmetics – work that will be possible once she has regained the use of her hands.

Thuli Thapa, 63, relaxes in the sun at the Khokana colony. Photograph: Sailendra Kharel/The Guardian

On the ward at Anandaban, Paniya has been watching Jodha Akbar, an Indian romantic drama, and playing with other young patients’ makeup. In the future, she’d like to run a stall – perhaps selling fruit and vegetables. She has also met a boy who also has leprosy, on the male ward of the hospital. She would like to get married one days, she adds, “if it’s a good man and he understands”.

It’s an 18-hour bus journey from her home near Biratnagar to Kathmandu: too far and too expensive for her parents to visit. Her mother has already stalked the boy from the hospital ward on Facebook. “She needs to be treated first and then we’ll worry about the boy,” says Sumitra.

Paniya is likely to spend the next six months in hospital while both hands are treated. The older women, or aunties, on the ward are looking after her, she says. They warned her the operation would be painful, but she says she felt fine. “The aunties, they are saying, ‘You are smiling – you don’t feel pain.’”