Experts have warned Australians of the proliferation of mosquitoes in summer and diseases carried by the insect. The mosquito population is forecast to hit their highest level in more than 10 years.

The hike in mosquitoes is largely due to the coldest start to summer in more than five decades and frequent rains which often leads to mosquito-borne ailments such as ross river fever and barmah forest virus.

Weather reports said the temperature reached 25.2 degrees Celsius in the first 13 days of December and reached a maximum of 25.6 on Sunday. It was also the wettest start to December since 2008 with 5.64 millimetres of rain fall.

The experts stressed that most mosquito species thrive on still water and summer heat.

Besides these two diseases, authorities are also on the lookout for a rise in number of cases of infection with the deadly horse-borne kunjin virus, particularly in western Sydney.

The insect develops the kunjin virus after it bites a mammal infected with it, which in turn the mosquitoes spread to humans.

"If you take the years from 2000 to 2010, it was the driest decade on record. Mosquitoes need water to breed, and with more humidity mosquitoes live longer. It's actually the older mosquitoes that transmit viruses rather than the younger one," The Herald Sun quoted Stephen Doggett, senior scientist at the Westmead Hospital's Department of Entemology.

In 2010, the kunjin virus took the lives of 10 per cent of horses in New South Wales after the virus crossed the Great Dividing Range. He pinpointed the areas at high risk for the kunjin virus in western Sydney as Baulkam Hills, Camden, Wisemans Ferry, Richmond and Windsor.

In Moora, the mosquitoes bit chickens that carry the virus and transmitted it to humans, confirmed Peter Williams, the manager of Health, Building and Planning Services in Moora.

Other ailments carried by the mosquito are the Murray Valley Encephalitis which has symptoms of fever, drowsiness, headache, stiff neck, nausea and dizziness. In severe cases, people infected could suffer from coma and may lead to permanent brain damage or death.