Singapore's rat problem: Common myths and health risks

SINGAPORE — Deanne Baptista, manager of local pest control company Origin Exterminators, has a story involving rats that sounds like a plot from a horror movie.

Her team was once called in after the rodents were sighted at a wet market. Fearing that the news could be bad for business, stallholders set up traps and cages.

Baptista quipped: "Basically, everyone thought of themselves as a rat catcher."

The situation turned comical when people could not remember what they placed where. They also did not know what to do once a rat was caught. And no one informed the pest control team about what they had done.

"So, by the time we initiated our action plan, we were greeted by not live rats but many decomposed ones," Ms Baptista recalled, adding that the stench was unbearable.

The incident is not a one-off. Rats have been making regular headlines all over the island in recent months.

In November 2023, a video of a rat lying on a tray of untouched food at Tangs Market went viral. A month later, a rat was discovered and captured in a cafeteria at the Institute of Technical Education College West in Choa Chu Kang.

Adding to the concern, veterinarians reported in January a surge in cases of leptospirosis, a bacterial infection primarily spread through the urine of rodents, which can affect both animals and humans.

In humans, a leptospirosis infection can result in symptoms ranging from a high fever and muscle pain in mild cases to bleeding in the lungs and meningitis in more severe ones.

Residents of Hougang have also complained of a persistent rat infestation, enduring for five years repeated damage to their car engine wires at a carpark in Hougang Avenue 8.

The three most prevalent types of rats in Singapore are the Norway rat (Rattus norvegicus), roof rat (Rattus rattus) and house mouse (Mus musculus).

The Norway rat, often referred to as the brown or sewer rat, can reportedly grow to the size of a kitten. 

Norway rats are excellent swimmers and prefer to seek food from a single source.

Roof rats, as their name implies, prefer elevated spaces. Agile climbers, they often take refuge in ceilings, like to travel in groups and are active during the night.

House mice, despite their small size, are prolific breeders, capable of giving birth to 20 pups each time. Theoretically, their numbers can expand from two to two million within 24 months in an environment free from predator and human intervention.

Rave Lee, assistant innovation manager at PestBusters, said: "In the industry, we have this rule of thumb: If your thumb fits into a hole, a rat can squeeze through because its body is so flexible.

"For a house mouse, the hole needs to be only the size of your pinky."

These commensal rodents, or rats that live in human habitats, are not unique to Singapore. Many other urban cities grapple with these species.

In New York City, where the rat population is reportedly three million, infestations have become so pervasive that the mayor appointed a "rat tsar" in April 2023 to address the issue.

So how many rats are there in Singapore? Pest control companies tell The Straits Times there is no precise data.

In October 2022, MP Mariam Jaafar asked in Parliament if there was a rat infestation problem on the island. Figures from the National Environment Agency — which conducts routine surveillance to pinpoint areas with rat activity — pointed to a fluctuating but persistent problem.

In 2020 and 2021, the average number of rat burrows detected in public areas during each two-month surveillance cycle were 4,300 and 3,900 respectively.

As social and economic activities resumed in the aftermath of Covid-19, the number for 2022 hovered around 4,100 as at August. Nonetheless, this figure was lower than the pre-Covid-19 count of 4,740 in 2019.

Dr Foo Foong Kuan, general manager of the technical and entomology department at pest control company Anticimex, said: "An infestation means rat sighting does not cease once we catch a rat. Rat activities continue persistently, making it nearly impossible to achieve zero rat count."

Pest control companies told ST in January that inquiries about rat infestation are up 25 per cent since November 2023. Several factors could have contributed to this uptick in rodent activity.

Lee of PestBusters noted that recent weather conditions, like the north-east monsoon, have brought heavier rain than usual to Singapore. The downpours could have flooded burrows or nests outdoors, compelling Norway rats to seek refuge indoors.

Ms Daphne Ling, technical executive and entomologist at Origin Exterminators, said there is also a rise in rat activities "especially when roadworks and tunnelling happen near the vicinity".

"Such disturbances make the rats feel unsafe about their surroundings, forcing them out of their nests and venturing to nearby food sources in search of safe shelters."

Infestations of roof rats and house mice that nest indoors are mostly the result of inadequate waste management, poor housekeeping practices, or the presence of gaps and openings in walls due to wear and tear.

Fighting infestation is complex, requiring more than just trapping and extermination, said pest controllers.

Infestations within household flats are relatively contained, but the scenario differs in large commercial buildings like shopping malls.

Such structures comprise common areas like corridors and stairs, alongside individual units and stalls. Rats, oblivious to such boundaries, will start exploring freely once they gain entry.

Dr Foo noted that inspections often reveal hidden complexities, such as obstructed views and inaccessible infestation sites.

"Typically, our inspection begins at the ceiling," she said. "When we open the ceiling panels, we often encounter numerous service lines like piping and wiring, which can obstruct our vision, posing difficulties to thoroughly assess an infestation."

Compounding the problem is the unwillingness of people to pay for pest extermination. Reasons, said exterminators, include a prevailing belief that rat elimination is a one-time solution, and the financial strain associated with continuous surveillance.

But Tang, a property manager, stands out as a notable exception. The 46-year-old, who declined to disclose her full name, said her company, which manages a commercial building, invests about $33,000 annually in pest control efforts.

This commitment is mainly driven by a desire to avoid any negative social media exposure about rat infestation, given the propensity of people, especially vloggers, to capture and share videos and images of buildings without prior notification.

Other factors complicating pest control include the challenge of coordinating across different stakeholders in commercial buildings and the lack of natural predators.

More importantly, there is a common misconception that rats are unintelligent, when in fact they are smart and adaptable.

"I remember working with a high-end shopping mall in Singapore," Baptista said. "The mall maintained a rigorous rat control programme, mainly targeting its numerous food outlets.

"These rats were so cunning that they knew the humans were pursuing them. So, they relocated to the retail areas and built their nests above shops selling designer bags and luxury items."

Lee said: "As professionals, it's crucial to understand the biology of pests before proposing control measures to clients. The public can also contribute by disposing waste responsibly."

Seasoned rat catchers said the fight is not just a task for professionals. Public involvement is crucial.

One hurdle, they added, is the notable disparity in public perception and response to rat sightings, depending on the location.

Ling said: "When people encounter a rat at a hawker centre or neighbourhood carpark, they often perceive it as a common occurrence. However, expectations are higher for shopping malls and upscale locations."

In reality, the public should prioritise hawker centres just as much, given that many people dine there, and they are closer to residential areas, she added.

Similar to Aedes mosquitoes that are responsible for dengue fever, rats, said Ling, also transmit numerous life-threatening diseases, including plague and rat-bite fever.

Baptista said: "There are considerable efforts and education for dengue fever, but not enough attention is given to rat infestation."

She referred to the incident of a rat falling from the ceiling of a basement foodcourt in Orchard Road, highlighting netizens' comments indicating the common occurrence of rats in neighbourhoods.

She added: "Until we collectively recognise that it's also not normal to see rats in hawker centres, I think the problem will not go away."

How to tackle a rat problem

Pest controllers said eradicating the menace involves more than just detecting and capturing the rodents. It also involves follow-up measures and effective pest management programmes.

Know the lay of the land

The initial step often involves requesting a floor plan to grasp the entire layout of the building.

This is particularly important for high-rise structures and shopping malls, where the layout is complex and comprises numerous units and tenants.

Next, rat catchers follow the signs of infestation, such as droppings, footprints and gnaw marks, as they navigate through the premises. Gnawing or chewing on objects, including doors, furniture and walls, is essential for rats to prevent their front teeth from overgrowing and piercing through their mouths.

This leaves behind distinct marks that darken over time. Based on these assessments, the pest control team comes up with a strategy.

Devise a plan

Control strategies typically range from recommending that clients keep their food in tightly sealed containers to sealing gaps with concrete to prevent rats entering from external areas.

Pest controllers from Origin Exterminators rely on a locally developed monitoring system that uses infrared technology and motion sensors to remotely detect rat movement.

The data collected enables pest controllers to strategically place glue boards and snap traps. The system will also provide alerts when rats are captured.

Depending on the severity of the infestation, the team will revisit the site weekly or fortnightly to assess whether the control strategy requires adjustments.

Monitor, monitor, monitor

If the client is receptive to a long-term pest management plan, the team will keep the monitoring system in operation and schedule visits once every month or every three to six months.

PestBusters uses a natural rat repellent composed of botanical and organic ingredients.

"Rats communicate through pheromones, an odour that signals to other rats that an area is safe for exploring," said Lee, the company's assistant innovation manager.

"Since rats follow the same path repeatedly, this repellent disrupts their pheromones, causing rats to feel disoriented. They become uncertain about whether to continue along their usual paths or where to go next."

This enables pest controllers to effectively locate groups of rats.

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This article was first published in The Straits Times. Permission required for reproduction.