Meet the team tracking monkey sounds in Singapore to stop emerging diseases

SINGAPORE - Over two dozen audio recording devices will soon be deployed across Singapore’s green spaces to record calls of the long-tailed macaque, the most common monkey species here.

It is not wildlife biologists who are eavesdropping on the monkeys, though, but a research team from the NUS Saw Swee Hock School of Public Health led by Associate Professor Kimberly Fornace.

They are on a mission to identify “hot spots” where an emerging disease caused by a parasite in these monkeys could potentially spread to humans.

Recording the calls of these social primates – which are the natural hosts of a parasite that causes malaria – will allow researchers to detect the animals’ presence in an area without having to physically see them.

The collected data can then be compared against information on places with high human and mosquito activity.

Pilot studies are currently being conducted on Pulau Ubin and in Mandai’s Night Safari, and the project will expand nationwide in September.

Malaria can be passed from monkeys to humans when a mosquito feeds on a parasite-infected macaque, and subsequently bites a person.

While such zoonotic transmissions of malaria are commonly documented in

places like Malaysia

, only a few cases have ever been recorded in Singapore.

According to the Ministry of Health’s HealthHub page, malaria brings about symptoms such as high fever, headaches, muscle aches and fatigue.

Singapore was declared malaria-free in 1982, which means the country had no locally transmitted cases for at least three consecutive years before that.

Despite this, the Republic needs to constantly be vigilant against the spread of diseases, due to its status as a transport hub.

The team plans to roll out the devices – dubbed AudioMoths – at 25 locations nationwide, pending final approval from the National Parks Board. The devices, costing about $120 each, will be deployed across a mix of park connectors, and forest cores and edges.

Of particular importance to the team are locations such as the Rail Corridor and northern park connector loop – the latter connects Admiralty, Woodlands, Mandai and the Central Catchment area.

Mr Shri Lak Nanjan Chandran, one of the researchers in the NUS team, said: “They are of interest because on top of being frequented by people, there’s a lot of green vegetation – so this will help us determine if the macaques are also using these spaces.”

The devices will be put up for a duration of eight months to a year, to detect variations in macaque activity during different seasons, such as over the north-east and south-west monsoon seasons, Mr Lak added.

In humans, malaria is typically thought to have been caused by four different parasites from the genus Plasmodium. These four parasites are known to naturally live, grow and multiply in human hosts.

But in recent years, a fifth parasite has come to global attention.

In 2004, a team of researchers sounded the alarm that the parasite Plasmodium knowlesi (P. knowlesi), which mainly replicates in long-tailed macaques, was also detected in humans.

Even Singapore’s National Centre for Infectious Diseases considers the disease caused by P. knowlesi an “emerging infection” in South-east Asia.

In 2007, Singapore recorded its first human case of locally acquired P. knowlesi infection, in a 20-year-old soldier in the Singapore Army, who had trained in forested areas where monkeys are commonly seen.

Subsequently, four more cases of human P. knowlesi infection were detected here in 2007, followed by another in 2008 – all among military personnel who had spent time in the forest.

In the Republic, no further cases were detected in humans after 2008.

A study published in 2021, however, found that the malaria-causing parasite was still prevalent within some macaque populations in Singapore.

P. knowlesi was detected in 80.5 per cent of 379 long-tailed macaques sampled between March 2009 and March 2017 from the Western Catchment area, a fully militarised zone.

Though monkeys living in other green spaces tested negative for malaria, Mr Lak said this may change as monkey troops are displaced by development.

Research projects like this can thus help to inform surveillance and mitigation strategies, he added.

For example, if hot spots where humans and animal vectors (animal carriers) intersect are known, government agencies like the National Environment Agency (NEA) could

deploy more traps in these places for vector monitoring.

Such traps include the Night Catcher, which was designed and optimised for use in forested areas, Mr Lak said.

The NUS team’s research is part of a larger bucket of projects funded by the Climate Impact Science Research programme, which is led by NEA.

These projects aim to study the impacts of climate change on various facets of life, including food security, water resources, energy and human health.

Disease risks are exacerbated by climate change, which bring about temperature and rainfall shifts that prompt animal populations to move into new areas, where they may have increased contact with humans.

Acoustic monitoring is not without its limitations, however.

According to Mr Lak, the recorded audio can be used to detect whether monkeys are present, but not how many there are.

He said: “For species as social as macaques, many of them may be calling at once, so we can’t really determine how many of them there are.”

These devices also ineffectively capture sound in green spaces where noise levels are high, such as parks close to the Changi and Seletar airports – where monkey calls may be masked by the roar of a passing plane.

Instead, acoustic monitoring data could be used alongside information collected via other methods, such as camera traps or researchers’ direct observations in the field, Mr Lak said.

Research projects such as this, which span domains like health and environmental studies, should be the way forward for the Republic, said Dr Chelsea Baker, a research fellow with the NUS team.

“Climate intersects with disease, and you can’t separate human health from animal and environmental health – these things are very intertwined and interconnected.”

Associate Professor Adrian Loo, deputy director of NUS’ Centre for Nature-Based Climate Solutions and who is not involved in the research, said the team’s work helps to fortify disease surveillance not just in Singapore, but also across South-east Asia.

He said: “The bioacoustics sensors can collect data 24/7. This can support field observations by researchers, which is usually limited by how much time one can spend in the field.

“They are also applicable not just in Singapore, but regionally, where vectors can have a larger range – bioacoustics may hence be helpful in extending coverage (over bigger areas).”

How does AudioMoth work?