Singapore's rat problems have worsened in the past year, with the authorities fielding many more complaints and discovering a sharp rise in the number of rat burrows.
Pest busters are also warning that the apparent explosion in the rat population could lead to diseases spreading and even fires in older buildings if the rodents gnaw on power cables.
The National Environment Agency (NEA) alone received 4,106 complaints about rats last year, about 35 per cent more than the 3,031 complaints in 2013.
Its latest round of inspections of public areas in October and November last year also uncovered about 10,000 rat burrows across the island, up from 6,400 burrows in the same period in 2013.
The Government has said that more than 35,000 burrows were found and the rats killed in the first eleven months of last year.
The NEA said close to 90 per cent of the burrows in its October- November inspection were in housing estates.
Improper storage and disposal of food waste could be one cause of infestations, it said, adding that the number of rats can multiply exponentially in a short time. For example, a single adult female Norway rat and its offspring can add as many as 2,500 rats to the population in a single year, it said.
"We are concerned about the increase in the number of burrows detected," said a spokesman.
Pest-control firms said they received up to 60 per cent more rat-related inquiries in the past year. PestBusters' technical director Eugene Surendra said: "For a small island like Singapore, the rat burrow figures are very alarming, and do not auger well for our reputation as a clean country."
If the rats come into contact with food, they could pass on diseases like salmonellosis, which can cause diarrhoea, fever, vomiting and even dehydration.
In 2012, a foreign worker's death was linked to leptospirosis, a bacterial infection spread from rats to humans.
Star Pest Control's general manager Bernard Chan said rats may gnaw on power cables to sharpen their teeth. "If the wires are exposed, people may be electrocuted by live wires during maintenance work, the electricity supply may become unstable and household appliances could catch fire," he said, although he has not seen such incidents.
The NEA said the key to getting rid of rats is removing their food sources and hiding places.
Malls, for example, should prevent rats from entering and breeding on their premises by plugging holes and gaps in their walls.
Everyone, from land owners to building managers and food shop operators, should store food and food waste in rat-proof containers, keep their premises clean and carry out routine pest-control checks and treatment, it added.
On its part, the NEA did more than 144,000 inspections on food shops last year. It has audited 85 out of over 200 malls to ensure that their rat-control measures are adequate.
The agency has also been working with town councils on a "rat attack programme" since 2011, which includes trapping the rats and sealing their burrows. Twelve public areas, including those in Geylang, Joo Chiat and Orchard Road, received special attention because of their high density of eateries and human traffic. The rodent situation in these enclaves "is largely under control", said the NEA, with the number of burrows found falling from 119 in March last year to 11 in December.