Authorities apprehend a major outbreak of the painful debilitating Ross River virus could be inevitable in the flood-ravaged western New South Wales. The region is reporting an explosion of mosquito population.
About 300 rural properties are still cut off by floodwaters in inland New South Wales.
Emergency aircraft are helping with supplies and medical support as well as stock movement and fodder drops to isolated rural properties.
Whatever the scale of such relief work, the mosquito menace looms large. It is felt that the activation of dormant mosquito eggs as floodwaters recede could have serious consequences for public health.
Ross River fever is the most common mosquito-borne viral infection in Australia. Symptoms include joint pains, swelling, severe headache, fatigue, muscle pains and weakness.
But almost three-quarters of people infected with the virus, which has no specific treatment, display no symptoms.
Rates of the disease - spread to humans by mosquitoes that have fed on infected kangaroos and wallabies - will at least double, said Stephen Doggett, a senior scientist at Westmead Hospital, and could rise much higher.
''One of the big concerns is that because it's been dry for so long, antibody levels have dropped in both the human and animal populations,'' Mr Doggett said. Low immunity to the virus, combined with a sudden surge in mosquito numbers, was ''a recipe for disaster ... The conditions are right there for a pretty serious outbreak.''
Further rains could amplify the epidemic, he said, and wet conditions extended the lives of the insects to a week or more, increasing their lifetime number of feeds to about four, which in turn increased the likelihood they would have previously bitten an infected animal, Julie Robotham said, writing for The Sydney Morning Herald.
But an outbreak was certain even if the land dried thoroughly and insect numbers dropped - because the proportion of wild marsupials and mosquitoes carrying the virus would already have increased, meaning transmission would continue.
Residents of flood-affected towns have reported plague numbers of large mosquitoes. Mr Doggett said these were likely to be of the species Aedes vittiger
, which grows to twice the typical size of other mosquitoes and lays its eggs alongside bodies of water.
NSW Health statistics show Ross River notifications have fallen recently in line with prolonged drought, and reached 900 last year, down from a more typical 1223 in 2006.
There was also a need to be alert for the possible spread of the much rarer but deadly Murray Valley encephalitis, which spread in similar conditions, Mr Doggett added.
While rushing repellents to the areas affected, the authorities are warning against skin and blood infections as also of spider and snake bites.