High rainfall and warm temperatures last summer have resulted in a near doubling of Ross River virus cases.
WA Health Department acting medical entomologist Peter Neville said La Nina weather conditions had resulted in increased mosquito breeding in wetlands and low-lying areas.
“The environmental conditions have really been suited to the mosquitoes themselves breeding in very large numbers, the virus as well, which has its own life cycle, and also host animals, things like kangaroos and wallabies,” he said.
Dr Neville said although cases were still being recorded, there had so far been 1579 incidents of Ross River virus reported in WA for last financial year.
“It’s almost double what we had last year in 2010-11,” he said.
“However it’s not an unusual figure to reach, back in 2003-04 we saw 1574 cases and then if we go back to 1995-96 we saw 1488.
“We sort of see this pattern associated with La Nina weather conditions every five or six or so years.”
The symptoms of Ross River virus include painful or swollen joints, sore muscles, skin rashes, fever, fatigue and headaches.
Symptoms can last from several weeks through to several months, depending on the patient.
Dr Neville said the worst affected areas were the South West, Great Southern and outer Perth suburbs near bushland.
He said it had been a very busy year following up patients who had come down with the virus and talking to local councils about mosquito control.