The increase can be blamed on a combination of factors, including regular rainfall, cooler temperatures and plentiful food supplies including from the large number of construction sites around Canberra.

Nicole Walker, from Armageddon Pest Control, said there were more calls coming from ''all over Canberra and not just one particular area''. The large number of infestations this year follows heavy demand for rat extermination last year when Rentokil ran out of baits.

Rentokil ACT branch manager Chris McCann said, ''As the temperatures in Canberra decrease, rats and mice search out areas for warmth and food and homes are an ideal source for both of these.

''Rats can fit through holes sized as small as a 10-cent piece and can pose a serious health risk to your family, so it is important to get professional help,'' Mr McCann said.

The rodents can spread disease through their bites, urine, tissue and their fleas. Rats can also destroy household items such as chairs, cables and food.

Rentokil is contracted to ANU's student accommodation complex UniLodge to prevent infestations in its newly constructed buildings that house about 2000 students.

The apartment complex is surrounded by construction sites and has an increased risk of rodents making themselves at home.

UniLodge ensures that baits are set in every cupboard of all of its apartment buildings and, according to Pascal Deschanel, a UniLodge building manager, it has not ''had no incidents to date''.

Pest Companies suggest that affected households and businesses should address the issue as soon as possible to avoid an unmanageable problem as rats breed very quickly.

An RSPCA spokeswoman said it encouraged people to go to the website for information on the most humane way to control infestations.