An integrated public health response to an outbreak of Murray Valley encephalitis virus infection during the 2022-2023 mosquito season in Victoria

Maxwell Braddick; Helen M O'Brien; Chuan K Lim; Rebecca Feldman; Cathy Bunter; Peter Neville; Christopher R Bailie; Grace Butel-Simoes; Min-Ho Jung; Aidan Yuen; Nicole Hughes; N Deborah Friedman

doi:10.3389/fpubh.2023.1256149

An integrated public health response to an outbreak of Murray Valley encephalitis virus infection during the 2022-2023 mosquito season in Victoria

Front Public Health. 2023 Oct 4:11:1256149. doi: 10.3389/fpubh.2023.1256149. eCollection 2023.

Authors

Affiliations

¹ Communicable Diseases Section, Health Protection Branch, Victorian Department of Health, Melbourne, VIC, Australia.
² Victorian Infectious Diseases Service, The Royal Melbourne Hospital, The Peter Doherty Institute for Infection and Immunity, Melbourne, VIC, Australia.
³ Victorian Infectious Diseases Reference Laboratory, The Royal Melbourne Hospital, The Peter Doherty Institute for Infection and Immunity, Melbourne, VIC, Australia.
⁴ Department of Infectious Diseases, Peter Doherty Institute for Infection and Immunity, The University of Melbourne, Melbourne, VIC, Australia.
⁵ Agriculture Victoria, Department of Energy, Environment and Climate Action, Melbourne, VIC, Australia.

Abstract

Introduction: Murray Valley encephalitis virus (MVEV) is a mosquito-borne flavivirus known to cause infrequent yet substantial human outbreaks around the Murray Valley region of south-eastern Australia, resulting in significant mortality.

Methods: The public health response to MVEV in Victoria in 2022-2023 included a climate informed pre-season risk assessment, and vector surveillance with mosquito trapping and laboratory testing for MVEV. Human cases were investigated to collect enhanced surveillance data, and human clinical samples were subject to serological and molecular testing algorithms to assess for co-circulating flaviviruses. Equine surveillance was carried out via enhanced investigation of cases of encephalitic illness. Integrated mosquito management and active health promotion were implemented throughout the season and in response to surveillance signals.

Findings: Mosquito surveillance included a total of 3,186 individual trapping events between 1 July 2022 and 20 June 2023. MVEV was detected in mosquitoes on 48 occasions. From 2 January 2023 to 23 April 2023, 580 samples (sera and CSF) were tested for flaviviruses. Human surveillance detected 6 confirmed cases of MVEV infection and 2 cases of "flavivirus-unspecified." From 1 September 2022 to 30 May 2023, 88 horses with clinical signs consistent with flavivirus infection were tested, finding one probable and no confirmed cases of MVE.

Discussion: The expanded, climate-informed vector surveillance system in Victoria detected MVEV in mosquitoes in advance of human cases, acting as an effective early warning system. This informed a one-health oriented public health response including enhanced human, vector and animal surveillance, integrated mosquito management, and health promotion.

Keywords: Murray Valley encephalitis virus; encephalitis; flavivirus; mosquito-borne disease; mosquitoes; outbreak; surveillance; vector-borne disease.

Publication types

Review

MeSH terms

Animals
Culicidae*
Disease Outbreaks
Encephalitis Virus, Murray Valley*
Encephalitis, Arbovirus* / diagnosis
Encephalitis, Arbovirus* / epidemiology
Horses
Humans
Mosquito Vectors
Public Health
Seasons
Victoria / epidemiology