Acute encephalitis is inflammation of the brain that is most commonly caused by viral or bacterial infection.
All seven cases in SA have required treatment in hospital.
Chris Lease, executive director of Health Protection and Licensing Services in the department, said authorities were investigating the confirmed cases for flavivirus, a mosquito-borne disease that can develop into encephalitis.
“All of these people required hospitalization with four people currently still in hospital, and one person having sadly passed away,” he said in a media release on Sunday, adding that the south east of Australia currently experiencing a La Nina weather pattern increases the risk of mosquito-borne diseases.
“Symptoms of encephalitis may include confusion, headaches, neck stiffness, tremors, drowsiness and seizures.”
In addition to the seven cases of acute encephalitis, there have also been 77 confirmed cases of the Ross River virus in SA, in 2022 so far, up from 48 at the same time in 2021.
Ross River is not lethal but can cause joint pain, fever and rashes.
The West Nile virus has been detected in New South Wales and mosquitoes carrying the Kokobera virus – a type of flavivirus – have been found in SA’s Riverland region.
“Most people who are infected with these viruses are asymptomatic or develop a mild febrile illness, but a small proportion of infected people, less than 1 per cent will develop encephalitis, which may be fatal or cause long-term neurological damage,” Lease said.