The potentially deadly mosquito-borne Murray Valley encephalitis (MVE) virus has been found in the South Australian Riverland.

Health authorities said testing of local birds, following the discovery of the virus in Victoria and New South Wales over summer, had returned positive results for MVE.

Birds were considered a good indicator of the presence of MVE because they had the ability to carry the virus without developing symptoms.

SA Health communicable disease control branch director Ann Koehler said the presence of the virus in birds would not necessarily have an impact on human health.

There had been no confirmed cases of MVE in humans in South Australia for the past 30 years.

"Only about one in 1000 people infected with the virus develop any symptoms," Dr Koehler said.

"Of those who do develop symptoms, approximately 20 per cent die from brain infection and 40 per cent of the survivors have permanent disability."

Symptoms of MVE include fever, headache, loss of appetite, nausea and vomiting, irritability, drowsiness, confusion and seizures.

It is transmitted by mosquito bites and is always present in parts of northern Australia.

After heavy wet seasons in the north it is sometimes found further south after being carried by various species of wild waterfowl.

Dr Koehler said while people should continue to take the usual protective steps against mosquito bites, there was no reason for Riverland residents to be alarmed.

"And the arrival of colder weather will have a significant impact on the amount of mosquitoes in the area, helping halt the breeding," she said.

Regular monitoring and control of mosquito breeding sites was being conducted by local councils, with support from SA Health.

In March this year MVE was found in two chickens around Kerang, 280km north-east of Melbourne.

A man died last month after contracting the virus in Western Australia's Kimberley region.