Researchers at NSW Health Pathology have published a study into the 2023 outbreak of Murray Valley encephalitis virus, including the impact of genomic sequencing in determining the spread of the disease and the crucial One Health collaboration to contain this emergent public health threat.

Mur­ray Val­ley encephali­tis (MVE) is a rare but poten­tial­ly seri­ous infec­tion of the brain caused by the Mur­ray Val­ley encephali­tis virus (MVEV) – a zoonot­ic flavivirus.It is spread by mos­qui­toes from infect­ed ani­mals to humans and although most peo­ple who are infect­ed do not expe­ri­ence any symp­toms, it has the poten­tial to cause per­ma­nent neu­ro­log­i­cal dis­ease or even death.

In 2023, there were 26 report­ed cas­es of MVE in Aus­tralia, includ­ing six in New South Wales.

A com­pre­hen­sive research study into the diag­nos­tic com­po­nents of the out­break was pub­lished in the pres­ti­gious jour­nal, the Lancet Microbe in June 2025 and involved pub­lic health lab­o­ra­to­ries across Australia.
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The research assessed how well diag­nos­tic plat­forms per­formed dur­ing the first six months of the out­break, as well as test­ing algo­rithms and the genom­ic char­ac­ter­is­tics of the virus to deter­mine the best way for­ward for future MVEV test­ing and surveillance.

The study also acknowl­edged the impact of a chang­ing cli­mate, with the out­break occur­ring after two unsea­son­ably wet sum­mers and a La Niña weath­er pat­tern which brought heavy rain­fall to the east­ern states of Australia.

Med­ical virol­o­gist and study author at NSW Health Pathology’s Insti­tute of Clin­i­cal Pathol­o­gy and Med­ical Research at West­mead Dr Jen Kok said it’s the largest case series of Mur­ray Val­ley encephali­tis virus from a diag­nos­tic viewpoint.

“We assessed fla­vivirus diag­nos­tics for all patients with sus­pect­ed Mur­ray Val­ley encephalitis.

“Twen­ty-sev­en patients were diag­nos­ti­cal­ly assessed for MVEV between Jan 1, 2023, and July 31, 2023, and they ranged from 6 weeks old to 83 years.

“We looked at the diag­nos­tics not just from stan­dard serol­o­gy, which is tra­di­tion­al­ly how these infec­tions have been diag­nosed, but also from PCRs, or nucle­ic acid detec­tion, which allows you to do genom­ic sequenc­ing of the virus.”

Using genom­ic sequenc­ing, the researchers found there were two con­cur­rent­ly cir­cu­lat­ing geno­types of MVEV in Australia.

One was cir­cu­lat­ing in the north and the south­east­ern parts of the coun­try, while the oth­er was only present in north­ern parts of Australia.

The impact of a One Health approach

Jen Kok said the research high­light­ed the impor­tance of a mul­ti­modal diag­nos­tic approach.

“The 2023 MVEV out­break brought togeth­er pub­lic health lab­o­ra­to­ries across Aus­tralia, along with ani­mal health groups, envi­ron­men­tal health organ­i­sa­tions and ento­mol­o­gists,” he said.

“It was real­ly the Japan­ese encephali­tis virus (JEV) out­break the year before in 2022 that paved the way for a One Health approach to diag­nos­tics and lab­o­ra­to­ry coor­di­na­tion for these outbreaks.”

The research also under­lined the impor­tance of con­tin­ued invest­ment in diag­nos­tic sur­veil­lance, par­tic­u­lar­ly with chang­ing weath­er pat­terns bring­ing unsea­son­al rain and increased trans­mis­sion of zoonot­ic dis­ease, which are infec­tious dis­eases trans­mit­ted between ani­mals and humans.

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“Sur­veil­lance needs to be done using mul­ti­ple meth­ods and organ­i­sa­tions,” he said.

“You need all those areas com­ing togeth­er, because no sin­gle sur­veil­lance method is com­plete, in the same way that no sin­gle diag­nos­tic method is com­plete for these outbreaks”.

The research con­cludes that ongo­ing One Health sur­veil­lance and col­lab­o­ra­tion is cru­cial for the ear­ly detec­tion of epi­demics, to enable prompt action to reduce the pub­lic health, ani­mal health, and envi­ron­men­tal impacts.

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