MURRAY Valley encephalitis virus (MVEV) cases surged in Australia last year, on the back of widespread flooding.

The mosquito-borne disease, which is endemic to the nation’s tropical north, re-emerged in south-eastern Australia during 2011.

There were 16 confirmed MVEV cases last year, resulting in three deaths and an additional suspected – but not confirmed – case in Victoria involving a 69-year-old man who also died.

This compared to zero MVEV notifications in 2010; in the period 2001 to 2009 there were 18 confirmed cases.

“MVEV is thought to be maintained in enzootic foci in the north of WA and the Top End of the NT in a cycle involving waterbirds and mosquitoes,” wrote Dr Jack Richards, of the Victorian Infectious Diseases Service at Royal Melbourne Hospital, and co-authors.
 
“Activity outside the enzootic areas is believed to follow the migration of infected waterbirds into flood-affected areas.
 
“…The recent activity of MVEV across Australia decreased with the arrival of winter, but the risk during this summer and the coming autumn remains uncertain.”
 
Dr Richards is urging healthcare professionals outside of usual MVEV-affected areas to be alert to heightened risk of the disease.
 
Initial symptoms include fever (often > 40°C) and headache.

Neurological features include lethargy, irritability, confusion and sometimes seizures occurring early.

There is no proven therapy, and treatment requires early transfer to a hospital with intensive care support.

MVEV infection is usually fatal in 15–30% of cases, with long-term neurological problems occurring in 30–50% of survivors.

“We know the one thing that will make a difference is getting them into ICU very quickly,” Dr Richards told MO.

Aside from the suspected case in Victoria, there were nine confirmed cases (one death) from WA, four cases (one death) from the NT, two cases (one death) from SA and one case from NSW.

Australia’s last major outbreak of MVEV was in 1974, with 58 cases identified and a mortality rate of about 20%.
 
MJA, online 23 Jan
 
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