The explosion of mosquitoes being seen and felt around Newcastle has been reflected in NSW Health's latest mosquito surveillance report.
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The report said numbers were at "very high" levels in Newcastle - the highest recording in the state, along with Nambucca.
Higher than average rainfall was creating "perfect breeding conditions for mozzies to lay their eggs," said Dr David Durrheim, of Hunter New England Health.
"All we need is a couple of really cold nights and the mosquito problem will go away, but on the coast it's still pretty warm."
Dr Durrheim added that climate change was causing "longer mosquito-active seasons".
"If the weather remains mild and we get big king tides, we might see another surge in mosquito numbers before winter hits us," he said.
The report said high tides over 1.8 metres were predicted from May 7 to 12, which could "trigger hatching" of the saltwater mosquito Aedes vigilax.
This mosquito type was a "vector of interest" for Ross River virus and Barmah Forest virus.
"In the right conditions with an inland breeze, they can travel up to 20 kilometres," Dr Durrheim said.
Another problem mosquito was Aedes notoscriptus, which "hangs around our houses and likes to breed in receptacles" like pot plants.
Hunter New England had recorded 78 cases of Ross River virus this year, rising from 47 over the same period last year.
There were 26 cases of Barmah Forest virus this year, compared to 48 over the same period last year.
These figures apply to people unwell enough to seek medical attention and be PCR tested.
"It's a reasonable year [for virus numbers]," Dr Durrheim said.
"The big issue is people let their guard down after Easter because they think we're heading into winter."
He said it was "still a sensible time to cover up and use repellant".
There are no vaccines for the Ross River or Barmah Forest viruses.
Symptoms following infection can include painful swollen joints, skin rashes, fever, fatigue, headaches and swollen lymph nodes.
Dr Durrheim said mosquitoes were "not born infected with these viruses".
"They have to feed on an infected reservoir, which we think is usually a marsupial [like kangaroos]," he said.
"This time of year, the viral load of infected marsupials is very high.
"A high proportion of roos will have Ross River. They don't seem to suffer much from it, but they're a source of virus for the mozzies."
Dr Durrheim said there were about 300 species of mosquitoes in Australia, but "only a limited number of them can transmit viruses".
"Adult mosquitoes only live up to three weeks in good conditions in mid-summer," he said.
They have a short period to get infected with the viruses and spread them, which diminishes as the weather cools.
