Three people died and 16 others were confirmed cases of Murray Valley encephalitis virus in 2011, according to an article in the Medical Journal of Australia.

Further outbreaks are possible this summer. There were no reported cases in 2010, and only four in 2009. The increase in the amount of cases came in the wake of significant regional flooding, with deaths occurring in Western Australia, South Australia and the Northern Territory.

The virus is endemic in northern Australia but has also reappeared in southeastern Australia last year. Experts say the risk during this summer and coming autumn remains unclear, particularly in areas where floods have occurred.

The virus causes brain inflammation, and is fatal in about 15-30% of cases, as well as causing long-term neurological problems in 30-50% of survivors. Only 40% of sufferers make a complete recovery.

Symptoms include fever, headache, lethargy, confusion, and sometimes seizures. There is not yet a cure or vaccine.