Cases of Ross River Fever have been recorded in Griffith and across the Murrumbidgee Local Health District.
Health authorities are urging people to take preventive action, particularly those who are spending the Australia Day public holiday camping.
Public health unit acting director Alison Nikitas said there had not been a significant cluster in one particular area.
"They've been fairly well-distributed along the border and out west," she said.
"We're alerting residents to the fact that we have had 18 cases of Ross River up to last Friday since the beginning of the year, when in the similar period of time last year, we had less than five," she said.
"We're asking people to take some precautions about being bitten by mosquitoes.
"Staying out of that early morning and dusk times when mosquitoes are out and active; wearing loose, long-sleeved clothing; and using personal protectants that contain DEET or picaridin.
"The other thing is just making sure that you have your house screened and remove any little buckets of water or any breeding environments."
MLHD has mosquito trapping stations at Albury, Wagga, Griffith and Leeton.
Ms Nikitas said there had been a detection of Ross River Fever in a mosquito caught at Griffith on January 19, but not at any other testing sites.
While the number of mosquitoes counted have been lower than expected, the higher rainfall this year and hot temperatures are optimal breeding conditions.
"The numbers in the report from the 16th [of January] were high in Albury, [and] not so high in Griffith," Ms Nikitas said.
"They were predicting that we would have high temperatures and higher cases this year in the inland regional areas.
"And you can actually have a rash in about the first seven to 10 days as well, which subsides.
"The more serious complications are people can get very swollen and sore joints. And whilst most people recover from Ross River, usually within a few weeks, those symptoms - the tightness, the sore and aching joints - can last for some months and can be quite debilitating."
A blood test early in the illness can indicate potential acute infection, followed by a test two weeks later.
People who develop fever and chills should also be tested for COVID-19, given the similarity in symptoms.