Emerging Genotype IV Japanese Encephalitis Virus Outbreak in New South Wales, Australia

Abstract

The detection of a new and unexpected Japanese encephalitis virus (JEV) outbreak in March 2022 in Australia, where JEV is not endemic, demanded the rapid development of a robust diagnostic framework to facilitate the testing of suspected patients across the state of New South Wales (NSW). This nascent but comprehensive JEV diagnostic service encompassed serological, molecular and metagenomics testing within a centralised reference laboratory. Over the first three months of the outbreak (4 March 2022 to 31 May 2022), 1,061 prospective samples were received from 878 NSW residents for JEV testing. Twelve confirmed cases of Japanese encephalitis (JE) were identified, including ten cases diagnosed by serology alone, one case by metagenomic next generation sequencing and real-time polymerase chain reaction (RT-PCR) of brain tissue and serology, and one case by RT-PCR of cerebrospinal fluid, providing an incidence of JE over this period of 0.15/100,000 persons in NSW. As encephalitis manifests in <1% of cases of JEV infection, the population-wide prevalence of JEV infection is likely to be substantially higher. Close collaboration with referring laboratories and clinicians was pivotal to establishing successful JEV case ascertainment for this new outbreak. Sustained and coordinated animal, human and environmental surveillance within a OneHealth framework is critical to monitor the evolution of the current outbreak, understand its origins and optimise preparedness for future JEV and arbovirus outbreaks.

Arthropod-Borne Flaviviruses in Pregnancy

“…The incubation period after a mosquito bite is 5–15 days. The virus replicates in local Langerhans cells and keratinocytes, and regional lymph nodes, after which it is carried by the lymphatic systemic into the thoracic duct and bloodstream [ 5 , 78 ]. JEV is neurotropic resulting in meningoencephalitis in approximately 1% of cases [ 79 ].…”

“…Viral shedding can be prolonged: for example, ZIKV RNA may be detectable for long periods in urine (median 24 days) and semen (median 25 days, but up to 370 days) [ 132 ]. Targeted NAAT assays carry higher diagnostic specificity but lower sensitivity due to short-lived viremia in many of these infections [ 5 , 125 ]. Loop-mediated isothermal amplification (LAMP)-based methodologies have been used for the detection of some flaviviruses such as JEV in resource-limited settings [ 133 ].…”

“…Non-targeted methods such as metagenomic sequencing carry promise in unveiling occult flavivirus infection if targeted sampling with expert guidance is performed, such as in cases of unexplained meningoencephalitis [ 5 , 134 ].…”

“… Global distribution of flaviviruses of importance in pregnancy including ( A ) Zika virus; ( B ) Yellow fever virus and dengue virus; and ( C ) Japanese encephalitis virus and West Nile virus [ 1 , 3 , 4 ]. Of note, the potential endemicity of JEV in Australia is currently under investigation in light of a recent outbreak in 2022 [ 5 ]. …”

Growth, Pathogenesis, and Serological Characteristics of the Japanese Encephalitis Virus Genotype IV Recent Strain 19CxBa-83-Cv

“…As of 22 October 2022, over 40 human JE cases, with seven fatal cases, have been reported [ 41 ]. The outbreak of JEV was first identified in swine and subsequently in humans, mosquitoes, and sentinel chickens [ 42 ]. Genetic analysis of the virus associated with the epidemics in 2021 and 2022 indicated that the virus was GIV JEV [ 38 , 40 , 43 ].…”