There is no vaccination or treatment for the virus, with people urged to protect themselves against mosquito bites.

MVE virus is spread by mosquitoes from infected animals to humans. In some rare cases it can cause severe neurological illness with headache, convulsions and reduced consciousness.

The virus cannot be transmitted between humans, and people cannot get the virus by touching an infected animal or eating animal products.

The primary hosts of MVE virus are waterbirds such as herons and egrets. Detection of MVE is likely related to recent rainfall and flooding.

Health Protection NSW executive director Dr Richard Broome said most infected people will not have any symptoms.

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"Only a small proportion of people infected with the virus will experience symptoms, which include fever, headache, nausea, vomiting, loss of appetite, diarrhoea, and muscle aches. Among those who get a severe infection, some may die or have lifelong neurological complications," he said.

While Australia is free of many mosquito-borne diseases such as malaria and dengue fever, Japanese encephalitis virus (JEV), Ross River virus and Barmah Forest virus are present.

The best way to avoid infection is to avoid being bitten by mosquitoes, which are most active between dusk and dawn.