Months of rain and flooding across large parts of NSW have created ideal conditions for an outbreak of Japanese encephalitis across the state.
Agriculture Minister Dugald Saunders said mosquito numbers are expected to increase in the coming weeks.
"As we recover from high rainfall and head into warmer temperatures, the conditions are ideal for Japanese encephalitis to spread," he said on Wednesday.
Livestock owners are being urged to watch for signs of the virus in their animals, with routine surveillance indicating it remains present in parts of regional NSW.
Japanese encephalitis is spread by the bite of infected mosquitoes and is more common in rural and agricultural areas.
Signs of infection include a high temperature, jaundice, lethargy, anorexia and neurological signs including a lack of co-ordination and impaired vision.
It does not present a food safety risk but the virus can cause reproductive failures in pigs.
Health Minister Brad Hazzard said Japanese encephalitis can also affect people, and he is urging people who live or work in areas identified as having the virus to get vaccinated.
"Take additional measures and wear light, long-sleeved clothing, apply repellent to exposed skin, improve drainage where possible to minimise stagnant water and cover windows and doors with insect screens," he said.
The vaccine is recommended for people aged two months or older who live or routinely work in 41 Local Government Areas with identified risk of the virus in southern and western NSW.