In a makeshift bamboo clinic, small children struggle to draw breath through surgical masks, victims of a forgotten but deadly disease that has torn through the teeming Rohingya refugee camps in Bangladesh.
Diphtheria had been all but eradicated in Bangladesh until last year, when more than 650,000 Rohingya poured across the border fleeing a bloody military crackdown in neighbouring Myanmar.
Packed into an area meant for a much smaller number of refugees and with little sanitation or healthcare, the new arrivals provided fertile ground for the highly contagious respiratory disease to take hold.
It quickly spread through the camps, with the World Health Organization reporting more than 3,600 cases.
The outbreak has already claimed the lives of at least 30 refugees, mostly children, while a handful of Bangladeshis living near the camps have also contracted the disease.
Carla Pla, head nurse at the specialist diphtheria unit run by medical charity MSF (Doctors Without Borders), said children were arriving with "severe" symptoms.
"This is a very challenging situation, because everyday there are coming more children, and the challenge to get the vaccine is also something that is very difficult," she told AFP at the unit.
Nearly 600 refugees have been referred there since it opened in December, putting enormous pressure on doctors also struggle to treat rampant malnutrition, water-borne disease and other diseases in the camps.
When AFP visited this week most of the patients were small children, some of them clearly struggling to breathe.
- Caught off guard -
Bangladesh authorities were prepared for other diseases and moved quickly to inoculate the new arrivals against cholera and measles to prevent a health disaster.
But the emergence of diphtheria, which causes difficulty breathing and can lead to heart failure, paralysis and death if left untreated, caught aid workers off guard.
"We were taken aback when tests confirmed diphtheria in the camps. It was a long-lost disease in our country," said Abdus Salam, the chief medical officer for Cox's Bazar district, where the camps are located.
"Immediately, we acquired vaccines from abroad for an emergency response."
In December, they launched a huge vaccination push. Nearly 320,000 children aged under 15 have now been inoculated and another 160,000 children are expected to receive the vaccine this month.
High rates of vaccination mean diphtheria has become increasingly rare in much of the world, although Yemen is currently suffering an outbreak.
But the Rohingya come from impoverished Rakhine state, where state-imposed restrictions have ensured abysmal living standards for the persecuted Muslim community, and many children are not vaccinated.
Pla said it was challenging for staff treating a disease that "only existed in the textbooks for all these years", with many doctors seeing live cases for the first time in their careers.
- Shortage of doctors -
Mohammad Hossain assumed his son, now being treated in the MSF clinic, had the same minor throat infection affecting other Rohingya children in the refugee camp.
"I thought it was tonsilitis. But the doctors said it was much more serious," Hossain told AFP, wearing a protective mask as he tended to the 11-year-old.
The appearance of diphtheria, long forgotten in many parts of the world, has compounded the misery for close to one million displaced Rohingya Muslims living in extreme hardship near the border with Myanmar.
Seven specialist diphtheria field clinics have been set up to treat the rising number of patients since the outbreak, said WHO's Southeast Asia emergency director Roderico Ofrin.
Together the wards house 400 beds for patients, but a shortage of doctors has required medics to be flown in from Britain and elsewhere to help battle the outbreak.
Treatment involves administering an antitoxin and antibiotics.
At the MSF ward, where Hossain's son Mohammad Rashed is making a slow recovery, medics wearing single-use scrubs work in tented-off wards treating patients.
Everyone coming into contact with the tents, set away in an isolated clearing, must wear masks and wash their hands in chlorinated water.
Preventing infected patients from coming into contact with the wider, largely unvaccinated population of Rohingya remains a priority, doctors said.
Rohingya community leaders meanwhile are trying to spread awareness about this resurgent disease to offset a full-blown epidemic.