A case of Japanese encephalitis has been identified in a man from the Riverland, where there is an ongoing flood emergency.
SA Health said the man, in his 80s, was the first identified case of Japanese encephalitis virus (JEV) in the state this mosquito season and was likely to have "recently acquired" the infection.
SA's Chief Public Health Officer Professor Nicola Spurrier said the man was recovering at home after spending a "number of days" in hospital.
"Fortunately even though he developed encephalitis he recovered and he's now back home so that's good news," she said.
"We know that people can be infected by this virus and have no symptoms whatsoever … but about one in 250 people develop symptoms and then we can make that diagnosis."
Symptoms of JEV include confusion, headaches, tremors, drowsiness, neck stiffness and seizures.
SA Health said there had been 10 confirmed JEV cases in South Australia this year and two deaths.
Professor Spurrier encouraged South Australians to remain vigilant and avoid exposure to mosquitoes, and get vaccinated against Japanese encephalitis if eligible.
"Think about going and getting it done now because of course you need a little bit of time for your immune system to kick in to protect yourself and you just don't know if the mosquito that bites you is the one that's carrying that disease," she said.
She said JEV vaccines were widely available in the Riverland region.
"We've had over 15,000 vaccines provided and we have 26,000 in total so there's still a lot of vaccine there and its not going to do any good for anybody sitting in the fridge, it needs to be in people's arms," she said.
Professor Spurrier said JEV was a "very serious condition" that "can affect anybody of any age".
Professor Spurrier said avoiding getting bitten was important for all South Australians, particularly as other mosquito-borne diseases had been detected in the environment.
SA Health recommends wearing long, lose-fitting and light-coloured clothing, applying mosquito repellent to exposed areas of skin and clearing mosquito breeding sites by emptying or covering anything that holds water.
Professor Spurrier said vigilance would likely be necessary for a prolonged period.
"I think we'll have lots of mosquitoes for quite a long time over this summer period," she said.
"As soon as we get this warm weather they will breed and they will explode in numbers.
"And there is a lot of water and as the main peak of the flooding goes through and that subsides, there will be lots of pools of water and its that stagnant water where mosquitoes just love to breed."
Free passenger ferry for Mannum
Meanwhile, the SA government has contracted a local cruise operator to provide a free passenger ferry service between Mannum and Cowirra in the Murraylands.
The temporary service aims to help locals cross the river for essential services while the regular ferries remain closed.
Mannum's upstream and downstream ferries, along with a number of others along the River Murray, were closed earlier this month due to rising floodwaters.
Four Knots Murray River Cruises will operate the 20-person ferry every 30 minutes from Tuesday.
Cruise operator Chad Blatchford said it was a "great lifeline for a small little business" after he had to close his usual cruise services due to the rising River Murray.
"People driving like an hour, half hour to Murray Bridge and back down, a lot of people just don't have those vehicles to get there and things like that … it means so much for the locals," he said.
Transport Minister Tom Koutsantonis said ferry services were "vital" and they will look at rolling out similar services in other River Murray communities where possible.
"Where we can do it we will and we'll look at other opportunities but this is the first one," he said.
