Tia Phalla, the vice chair of the National AIDS Authority, remembers the darkest chapters of the country’s fight against HIV, like in 1995, four years after the first case of the virus was detected in Phnom Penh, when on average 65 Cambodians were infected every day. By the end of the 1990s, the country had the highest new infection rate in the region, and an epidemic on its hands.

But since then, the Kingdom’s HIV/AIDS programme has distinguished itself as a model for treatment and prevention. This year, there are just two new cases on average each day and four of every five currently infected with the virus have access to treatment.

But Cambodia now finds itself at a crossroads, in part because of its own success. With outsider funding dwindling since 2010, the government is being asked to pick up more of the tab. If it doesn’t, the programme faces severe shortages, according to health workers and experts within the HIV/AIDS programme.

For Phalla, who was involved in the 1992 founding of the National Committee to Fight AIDS, the stakes could not be higher. About 120,000 Cambodians have died from the virus since the epidemic emerged, but more than half a million other deaths have been averted by the country’s successful response, according to United Nations estimates.

Phalla said that if Cambodia hadn’t taken quick action – mobilising across ministries and in partnership with NGOs and global health organisations – the scale of tragedy could have been close to the suffering endured in the killing fields of the Khmer Rouge.

The possibility of losing ground after decades of progress weighed on him.

“My dream is that this killing field is not coming,” he said.

Cambodia has been dependent on external funding throughout its fight against HIV/AIDS, but since 2010 the pool has been slowly shrinking.

Outgoing UNAIDS Country Director Marie-Odile Emond said that in response national contributions have increased slowly, but not at the same rate.

“It’s really . . . urgent for the government to increase its national funding contribution because with all the estimates that we’ve done, there’s still sufficient funding for 2017, but from 2018 [and on], unless the government increases its contribution, we are going to have a funding gap for services,” she said. “It’s very dangerous. If there is a funding gap and the government is not able to invest, then services will drop and we are losing some of the gains.”

According to Emond, the government will have to invest at least $4 million – up from $1.5 million this year – beginning in 2018 to avoid any gaps in services, at a time when its goal is to eliminate new infections by 2025.

The two largest donors to the program, the Global Fund and USAID, not only have decreased funding, but have also imposed stricter co-financing requirements, whereby in order to receive funding a government contribution must increase each year.

Global Fund spokesman Seth Faison said the country’s co-financing requirement for next year is yet to be determined, but earlier this month Phalla said the Kingdom will need to invest $3.2 million in each of the next three years to have access to the Fund’s $41.6 million.

Dr Ly Penh Sun, the director of the Ministry of Health’s National Centre for HIV/AIDS, Dermatology and STDS (NCHADS), said he was confident that the Finance Ministry would allocate the necessary funds. “The government of Cambodia will continue to commit to fund the gap,” he said.

However, Phalla noted a handful of national spending priorities, especially at a time with two costly upcoming elections that the government will need to pay for. It is also struggling to figure out a long-term sustainable plan for the Kantha Bopha Children’s Hospitals after Beat Richner, the founder, announced in March that he was stepping down from his post, with the hospitals eventually coming under government management.

According to the Global Fund’s Faison, the funding cuts to Cambodia’s HIV/AIDS sector are directly linked to its successes.

“The Global Fund allocation is based on disease burden and income level of each country where we invest, which is more than 100 countries,” he wrote in an email. “Allocations go up where the problems are greater, and go down where progress is being made.”

The second largest donor to the sector, USAID, has reduced its contribution from a high of $18 million in recent years to $11 million in 2017, Phalla said. USAID will also only fund technical assistance, not services, after November.

Jay Raman, a spokesman with the US Embassy, said assistance in HIV/AIDS “is substantial and has produced outstanding results”, but declined to comment further.

One of the other consequences of funding shortfalls is fading expertise among health workers. Many of the locals involved in the fight against the virus since the early 1990s are retiring. With little money going towards NGOs working in HIV/AIDS, the young generation of health workers, and civil society organisations themselves, are shifting elsewhere. That leaves the approximately 70,000 Cambodians living with the virus potentially neglected.

For Emond, whose tenure as UNAIDS country director came to an end on May 12, the country in some ways has more to lose than those still grappling with a full-blown epidemic.

“If you reduce treatment access or prevention work, which is also very important, then you immediately have an impact on people’s lives, but there is also a risk that the epidemic may re-bounce,” she said.

“And then we are going to have to invest more later.”

Other countries in the region, such as Vietnam and Myanmar, have endured similar cuts but managed to increase their national contributions, she added.

“Being one of the first countries to reach the end of the tunnel means you are facing challenges that other countries are not yet seeing because they are behind in the tunnel,” she said.