“It’s always the rainy season; sometimes the rainier season,” said Freeman. His teams distribute nets to all of PNG’s 20,000 villages – and keep track of their work. “We can tell you the history of the nets in every one of them,” he said.

It has been a group effort. A malaria adviser in WHO’s country office works with Freeman’s teams, helping determine how many nets are needed and providing technical guidance. WHO also sets global policy and targets, and helps translate these into country-specific plans.

Australia has contributed financial resources, and Population Services International, a US-based NGO, has deployed outreach officers to teach communities how to use mosquito nets consistently and correctly, and how to identify the symptoms of malaria and seek treatment quickly.

The efforts have paid off. “Malaria has dropped like a stone,” Freeman said.

“We have seen a massive decrease in the incidence,” agreed Dr Manuel Hetzel, an epidemiologist who evaluated the malaria-control program from 2008 to 2012 while working for the Institute of Medical Research in PNG.

Two advances are responsible for PNG’s progress: the near-universal distribution of long-lasting insecticidal nets and an infusion of money for diagnosis and treatment of malaria.

Armed with a Global Fund grant of $US109 million in 2009 and guided by WHO’s technical recommendations, PNG distributed more than 7.5 million nets during the following six years.

The effort has halved the incidence of malaria from 400 cases per 100,000 population to 200.

Between 2009 and 2015, the incidence of malaria admissions to public health facilities dropped by 83%, and malaria death rates in health facilities fell by 76%.

Bednets are not the only interventions credited for the advances: surveillance, diagnosis and treatment also play roles in prevention, said Dr Rabi Abeyasinghe, who coordinates malaria activities for WHO in the Western Pacific Region, where malaria is endemic in 10 of its 37 countries.

Surveillance helps planners identify where to distribute bednets, and treatment of individuals prevents other cases from occurring. “If there are people with malaria parasites walking around, the mosquitoes will get infected and transmit it to other people,” he said.

But the advances are in peril.

As donors seek maximum impact for their investments, and focus on countries that need support most, investment in middle-income countries with a low-to-moderate disease burden is declining. Malaria programs in these countries will need to explore other funding arrangements, including increased support from domestic resources.

For example, the Global Fund, which bankrolls approximately 80% of the financing for malaria programs, has cut its funding to PNG by about 50%.

“Donors are interested in countries that have a high burden of malaria but a low income,” said Stefan Stojanovik. “PNG is a low-middle income country.”

The Global Fund and other donors are shouldering much of the financial burden, but governments will have to contribute more resources themselves if they are to control malaria in a sustainable way, said WHO’s Dr Jan Kolaczinski.

 “The lower the burden, the harder it is for malaria programmes to make the case for government funds, as ministers will shift their attention to diseases that pose a more apparent public health problem,” he added.