Residents of New South Wales and Victoria face alarming threats of a rare avian disease this summer that health officials said was being caused by mosquitoes.

According to Jeremy McAnulty, director for NSW Health's Centre for Health Protection, these specific mosquitoes that are prevalent from towns near the Murray River to Victoria, cause Murray Valley Encephalitis (MVE) and was first observed affecting poultry stocks in southwest NSW.

"Murray Valley encephalitis or MVE is a rare infection of humans in New South Wales ... when it does occur it's carried by mosquitoes and is primarily a virus of birds, so mosquitoes transmit it between birds and occasionally people get in the way," McAnulty told ABC News.

Health officials from both states have issued advisories warning residents to be wary of these mosquitoes and once they suspect of bites, they need to be aware of MVE's symptoms.

Immediate symptoms, according to McAnulty, are severe headache, fever, neck stiffness, drowsiness and confusion but he reminded that "99 per cent or more of the time, an infected person will remain totally well and not get any symptoms."

"But a small proportion of people who are infected will get an illness that ranges from being fairly mild to very severe and fatal," McAnulty added.

Health officials said that the disease is so rare the last recorded case in Australia was way back in the 1970s, which affected some 80 patients then, with cases again emerging last summer.

"Most recently in the last summer we saw two people with the infection, one of whom didn't have symptoms was found by testing and one who did have symptoms and recovered," McAnulty was quoted by ABC as saying.

"In about a third of people who get the symptoms it can be fatal and in about another third they can have long-term ongoing neurological problems. So it can be a nasty disease if you get it," the NSW health official added.

MEV leads to brain infection or meningitis, which McAnulty stressed, is the more serious complications attributed to the disease, stages of which when reached by an infected person could lead to death.

Yet the infections can be shunned by avoiding contacts with the mosquito carriers, which health officials said were most active during dusk and dawn, time of the day that people should be protected when they venture out.

Protection is best offered by wearing long sleeves and long pants, McAnulty said, and by using insect repellents containing DEET or picaridin, to effectively fend off these mosquitoes.