It would be tough to find a location more hospitable to the spread of malaria than PNG.
"This country has very, very difficult geography, with little infrastructure," said Tim Freeman, a logistician for Rotarians Against Malaria.
At 61, Freeman has spent more than half of his life fighting malaria. He is the kind of guy you want nearby if your car gets stuck in the mud, which he has seen happen a lot while overseeing the distribution of more than 5 million insecticide-treated mosquito nets in PNG.
It contains areas so remote that, until the 1990s, tribes were being discovered whose members had had no previous contact with outsiders.
Even now, some villages have no roads. Delivery of nets can require an airplane, helicopter, boat, truck and days of walking - often in the rain. "It is 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," Freeman said.
It has been a group effort. A malaria adviser in the World Health Organisation 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 (PSI), a US-based nongovernmental organisation, 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.
Both Rotarians Against Malaria and PSI implement their malaria activities through financial support from the Global Fund to Fight AIDS, Tuberculosis and Malaria.
The efforts have paid off. "Malaria has dropped like a stone," Freeman said.
"We have seen a massive decrease in the incidence," agreed Manuel Hetzel, PhD, 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 (LLINs) and an infusion of money for diagnosis and treatment of malaria.
Armed with a Global Fund grant of $109 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 slashed the incidence of malaria in PNG since 2004, 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, he said. "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 programmes 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 programmes, 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 the Global Fund's 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 Dr Jan Kolaczinski, who moved this year to WHO from the Global Fund.
"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.