The warning comes because recent heavy rains followed by hot weather provide ideal conditions for mosquito breeding.

Pools of stagnant water have turned many backyards into the perfect breeding ground for mosquitoes. It only takes two to three weeks to produce large numbers of mature mosquitoes.

While mosquito bites are generally no more than a nuisance, they can transmit infections such as Ross River virus or Barmah Forest virus.

This happens more commonly in rural areas but cases have occurred in the urban fringe areas of northern and western Sydney in recent years.

The Hawkesbury area, due to its rural setting, contains the highest prevalence of Ross River virus and other mosquito-borne viruses in the Sydney West Area Health Service area, per person of population.

Ross River virus and Barmah Forest virus infection can cause an influenza-like illness, with fever, chills, aches and pains in the muscles and joints and, sometimes, fatigue, swelling of joints and a rash.

It may last a few days to weeks and occasionally causes episodes of illness for months to a year.

The incubation period (the time between mosquito bite and illness) ranges from three days to three weeks.

Anyone can contract these diseases and in the western Sydney area, 23 human cases are reported on average each year.

However the number of cases notified can vary widely depending on rainfall and temperature patterns.

People living in areas near constructed or natural waterways should take particular care.

Mosquito trapping is conducted at a number of locations throughout the Western Sydney area during the breeding season to determine whether mosquitoes are carrying viruses.

Trapping is conducted by local councils and testing is performed at the Centre for Infectious Diseases and Microbiology Laboratory at Westmead Hospital.