Riverina residents and those in the border region are being urged to remain vigilant against mosquito bites in the wake of NSW Health confirming one "highly probable" case of the virus in a resident of the border region.

As of Sunday The Daily Advertiser understands there are additional cases under investigation in NSW, expected to be confirmed in the coming days.

The single human case remains "highly probable", with the person in a serious but stable condition in the ICU. This follows on from earlier reports of the rare disease being detected across three Riverina piggeries in Corowa, Grong Grong and Stockinbingal.

This follows on from earlier reports of the rare disease being detected across three Riverina piggeries in Corowa, Grong Grong and Stockinbingal.

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Previously, locally acquired cases of the virus have never been found in NSW in either animals or humans, instead found in far northern Australia and neighbouring countries. JEV can cause severe neurological illness and there is currently no specific treatment.

NSW Health acting chief health officer Dr Marianne Gale has flagged the Murray River and its branches as areas where people should remain especially careful when undertaking outdoor activities such as camping and fishing.

"People should be particularly vigilant given the recent wet weather conditions, which have led to very high mosquito numbers that may increase further in the coming days and weeks," she said.

NSW Health says it is working closely with the Department of Primary Industries and other state agencies to determine the extent of the virus' spread, through animal testing and mosquito monitoring.

"Mosquito control activities are being carried out in the vicinity of farms where pigs are confirmed to have been infected by JEV and NSW Health is arranging vaccination of workers on affected farms," a NSW Health spokesperson added.

JEV is a viral illness, spread by mosquitos, that can infect both animals and humans. The virus cannot be transmitted between humans and cannot be caught by eating pork or pig products.

The virus has been confirmed in samples from a number of pig farms across regional NSW, including the Riverina.

Last week Murrumbidgee Local Health District's director of public health Tracey Oakman said only one per cent of people who contract JEV become unwell, "but they can become very, very unwell".

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