Papua New Guinea (PNG) is among the world’s most at-risk countries for malaria, with around 1.5 million cases estimated in 2023. Researchers at the Australian Institute of Tropical Health and Medicine (AITHM) estimate that, with a growing population and rising temperatures, 74 per cent of the population could be living in malaria territory by 2040.
The PNG government is hoping to eliminate malaria in the country by 2040. This is why Associate Professor Stephan Karl — together with his fellow researchers from the Papua New Guinea Institute of Medical Research in Madang, the University of Queensland and the Burnet Institute in Melbourne — decided to assess the potential malaria risk for the PNG population for the same time frame.
Associate Professor Karl says that PNG is a country defined by its mountains, with the central mountain range reaching altitudes of 3,000 to 4,000 meters. “The valleys between the mountain ranges have high population densities, and about 40 per cent of the population lives in these highland valleys,” he said. “People preferred to live there because there was no malaria.”
Climate change, however, has already led to frequent malaria outbreaks in the highlands in recent years, and Associate Professor Karl knows that this is only the beginning. “Malaria is a temperature-dependent disease. Malaria mosquitos are most dangerous in the 25-30 degrees Celsius range, because the malaria parasite can develop quickly, and mosquitos lay more eggs,” he said.
“As it gets colder up in the mountains, malaria cannot be transmitted because the mosquito life span is too short,” he said. “However, if the temperature rises in the mountains, then malaria mosquitos will be able to conquer new territories.”
For this study, the researchers relied on recorded temperature data from 1960 to 2019. “We used a relatively conservative model, a middle-of-the-road scenario, to calculate how malaria is probably going to impact the PNG highlands by 2040,” Associate Professor Karl said. “We assumed that we might experience a temperature increase of approximately three degrees Celsius from pre-industrial times to 2100.”
Associate Professor Karl said that there are also other factors that influence whether malaria transmission can occur — if humans do not inhabit an area, there won’t be any malaria cases, for example. “We also need to consider how the population expands over the years, and if there is water where mosquitos can lay their eggs, among other things”, he said.
The team used publicly available satellite data and mapped everything on a five-by-five kilometre grid that shows the likelihood of malaria transmission for each square.
Associate Professor Karl said that the team worked on two scenarios. “One assumes that there is no climate change and only population growth. We calculated the increase in the number of people that may live in malaria risk areas in 2040. PNG currently has a population growth rate of about 3.2 percent. So, even without climate change, the population will increase,” he said.
The second model took population growth and climate change into consideration. “We found that the altitude at which malaria can be transmitted could increase by about 260 meters by 2040,” he said. “That doesn't seem like a lot. But the population density in the highlands, and particularly in the highland valleys, is very high.
“What we found was that the number of people living in malaria-endemic areas in PNG will approximately double between now and 2040,” Associate Professor Karl said.
About 60 per cent of the population — more than six million people — lives in the country’s coastal areas, in which malaria is already endemic. “With climate change, pushing malaria into the highlands, this will rise to 74 per cent,” he said. “Accounting for population growth, an additional 6 million people may be living in malaria territory in 2040 in PNG alone.”
Associate Professor Karl said that these numbers are important indicators for PNG’s National Malaria Control Program and the National Department of Health. “And these numbers are also important because we need to raise more awareness, and we need additional funding if we want to succeed in ultimately eliminating malaria by 2040.”
The article is published at: https://pubmed.ncbi.nlm.nih.gov/41020062/.