Drones are being used to track monkeys deep in the Malaysian forests to understand better how the primates are passing a rare strain of malaria to humans. Malaysian Borneo has seen a surge in cases of “monkey malaria,” a strain of the disease that normally only affects macaques, caused by the parasite Plasmodium knowlesi. The disease is commonly misdiagnosed because it looks the same as a mild form of malaria under a microscope. But the monkey strain – which accounts for 69% of all human malaria cases in Malaysia – has a high fatality rate due to the parasite’s rapid replication cycle. A team of scientists from the London School of Hygiene and Tropical Medicine has been running a research programme using drone technology, called the Monkey Bar Project, to monitor the spread of the disease.
Cally Roper, professor in malaria genetics, said: “This unusual form of malaria was previously only found in the macaque population and was very rare, but the number of cases has been increasing and it appears people are at risk when coming into contact with the monkeys.” The latest data available shows the number of cases among humans in Malaysia has increased from 376 cases in 2008 to 1,604 in 2016. Eight deaths from the disease were also reported in 2016. Researchers have found a strong link between deforestation and a higher incidence of the disease among humans. It’s thought to be because monkeys are forced out of their natural habitat towards farmland or to seek out food sources. Studies revealed that where substantial areas of forest had been cleared in the past five years, there was a 1.5 to three times higher incidence of “monkey malaria. Drones are used to monitor changes in the landscape like the clearing of forests for agriculture, where there is primary or secondary forest or plantations,” said Roper. “It can then be inferred what forest cover is most conducive to the spread of this form of malaria.”
Using drones is cheaper than obtaining satellite images, and can give a more detailed picture of what the ground cover looks like in areas where the disease is prevalent. A £10,000 fixed-wing drone operated by a laptop is used to monitor the forests by running for up to 40 minutes in grid patterns, taking photographs that are then knitted together to form a high-resolution map. The Monkey Bar Project has been collecting data in this way since 2013 but more recently has started using thermal imaging to follow the movements of the macaque monkeys. Research fellow Kimberly Fornace, who has been mapping deforestation in Borneo’s northern Sabah region, said, “We are still optimising the process, but the hope is to have a rapid way of estimating how many monkeys are in a particular area without having to wander around the jungle at night looking for them.” The team have also attached GPS collars to individual monkeys within macaque troops living close to humans and tracked them using a drone. Fornace said, “We’ve used it on several monkeys and on one in particular where we knew there was a large area of land being cleared so we could see where it was moving in response.”
All the data collected is from long-tailed macaques, the most common species of the primate in Sabah. The majority of macaques in the area test positive for P knowlesi – in some areas there is a prevalence of up to 86%. However, the parasite does not appear to affect the monkeys. Macaques are relatively well adapted to living close to people and are moving closer to humans to scavenge for food as forests are cut down. Fornace said, “[The rise in cases] is a cause for concern because Malaysia has made huge gains in controlling other forms of malaria and the P knowlesi strain now makes up the vast majority of cases.” She added, “It is also worrying because what has worked for other strains of malaria such as … doing mass drug administrations – you obviously can’t do with monkeys. There is no way of stopping the transmission.” Instead, it is hoped the latest technology will help experts predict where outbreaks could occur to inform malaria control programmes.
The Monkey Bar Project is due to publish the findings of its five-year study later this year, but already the data collected by the drones have had some positive impact. The team say public health officials have been more proactive about malaria prevention in areas where tree clearing is taking place – such as using insecticide sprays and distributing bed nets. Drone technology is increasingly being used in the fight against malaria and other diseases. In Zanzibar, drones are being used to survey malaria hot spots and identify water-laden areas where malaria-carrying mosquitoes are likely to breed.
The next phase of the project – run by Aberystwyth University in Wales, in partnership with Zanzibar’s Malaria Elimination Programme – will be to bring the drone imagery to smartphones to guide insecticide spraying. Andy Hardy, lecturer in remote sensing at Aberystwyth University, said: “I conducted a proof study last year which found we can use drone technology to rapidly and accurately map malarial mosquito habitats. “From July this year, we will roll this out across Zanzibar, flying over target areas – such as a rice paddy, which would take about 30 minutes.” The images can be quickly processed on a standard laptop to produce a map of the area that is scanned for water bodies and all locations logged. This is then uploaded to an app used by spraying teams to help them better navigate the landscape and track their progress. The use of such technologies to map and tackle the spread of malaria will be discussed at the London malaria summit on Wednesday. Heads of state are to convene to announce some new commitments to tackle the disease.
Credit: Hannah Summers for The Guardian, 17 April 2018.