Clinical and radiological predictors of outcome for Murray Valley encephalitis

Therapeutic Plasma Exchange for Murray Valley Encephalitis: A Case Report and Review of Clinical Features, Diagnosis, and Challenges in Management

We report the case of a 62-year-old male who presented to the Emergency Department (ED) with altered mental status following a motor vehicle accident. He was transferred to the Intensive Care Unit (ICU) with worsening of his neurological status and subsequently diagnosed with Murray Valley encephalitis: a serious but rare condition caused by infection with Murray Valley encephalitis virus (MVEV). He continued to deteriorate despite treatment with antivirals, glucocorticoids, and therapeutic plasma exchange (TPE) in addition to supportive care and eventually succumbed to his illness. In this report, we review the clinical course, pathophysiology, diagnosis, and characteristic radiological features of Murray Valley encephalitis and highlight the challenges in treating this potentially devastating disease.

Japanese Encephalitis Virus: The Emergence of Genotype IV in Australia and Its Potential Endemicity

A fatal case of Japanese encephalitis (JE) occurred in northern Australia in early 2021. Sequence studies showed that the virus belonged to genotype IV (GIV), a genotype previously believed to be restricted to the Indonesian archipelago. This was the first locally acquired case of Japanese encephalitis virus (JEV) GIV to occur outside Indonesia, and the second confirmed fatal human case caused by a GIV virus. A closely related GIV JEV strain subsequently caused a widespread outbreak in eastern Australia in 2022 that was first detected by fetal death and abnormalities in commercial piggeries. Forty-two human cases also occurred with seven fatalities. This has been the first major outbreak of JEV in mainland Australia, and geographically the largest virgin soil outbreak recorded for JEV. This outbreak provides an opportunity to discuss and document the factors involved in the virus' spread and its ecology in a novel ecological milieu in which other flaviviruses, including members of the JE serological complex, also occur. The probable vertebrate hosts and mosquito vectors are discussed with respect to virus spread and its possible endemicity in Australia, and the need to develop a One Health approach to develop improved surveillance methods to rapidly detect future outbreak activity across a large geographical area containing a sparse human population. Understanding the spread of JEV in a novel ecological environment is relevant to the possible threat that JEV may pose in the future to other receptive geographic areas, such as the west coast of the United States, southern Europe or Africa.

A Journey to the Central Nervous System: Routes of Flaviviral Neuroinvasion in Human Disease

Many arboviruses, including viruses of the Flavivirus genera, are known to cause severe neurological disease in humans, often with long-lasting, debilitating sequalae in surviving patients. These emerging pathogens impact millions of people worldwide, yet still relatively little is known about the exact mechanisms by which they gain access to the human central nervous system. This review focusses on potential haematogenous and transneural routes of neuroinvasion employed by flaviviruses and identifies numerous gaps in knowledge, especially regarding lesser-studied interfaces of possible invasion such as the blood-cerebrospinal fluid barrier, and novel routes such as the gut-brain axis. The complex balance of pro-inflammatory and antiviral immune responses to viral neuroinvasion and pathology is also discussed, especially in the context of the hypothesised Trojan horse mechanism of neuroinvasion. A greater understanding of the routes and mechanisms of arboviral neuroinvasion, and how they differ between viruses, will aid in predictive assessments of the neuroinvasive potential of new and emerging arboviruses, and may provide opportunity for attenuation, development of novel intervention strategies and rational vaccine design for highly neurovirulent arboviruses.

Fatal Infection with Murray Valley Encephalitis Virus Imported from Australia to Canada, 2011

Murray Valley encephalitis virus (MVEV), a flavivirus belonging to the Japanese encephalitis serogroup, can cause severe clinical manifestations in humans. We report a fatal case of MVEV infection in a young woman who returned from Australia to Canada. The differential diagnosis for travel-associated encephalitis should include MVEV, particularly during outbreak years.

Neurological disease caused by flavivirus infections

The Flavivirus genus contains dozens of species with varying geographical distributions. Most flavivirus infections in humans are asymptomatic or manifest as a non-specific febrile illness, sometimes accompanied by rash or arthralgia. Certain species are more commonly associated with neurological disease and may be termed neurotropic flaviviruses. Several flaviviruses endemic to Australia and our near northern neighbours are neurotropic, such as Murray Valley encephalitis virus, West Nile (Kunjin) virus and Japanese encephalitis virus. Flavivirus neurological disease ranges from self-limiting meningitis to fulminant encephalitis causing permanent debilitating neurological sequelae or death. The recent Zika virus outbreak in South America has highlighted the dramatic effects of flavivirus neurotropism on the developing brain. This article focuses on the neurotropic flaviviruses endemic to Australia and those of international significance.

Differential Diagnosis of Flavivirus Infections in Horses Using Viral Envelope Protein Domain III Antigens in Enzyme-Linked Immunosorbent Assay

In Australia, infection of horses with the West Nile virus (WNV) or Murray Valley encephalitis virus (MVEV) occasionally results in severe neurological disease that cannot be clinically differentiated. Confirmatory serological tests to detect antibody specific for MVEV or WNV in horses are often hampered by cross-reactive antibodies induced to conserved epitopes on the envelope (E) protein. This study utilized bacterially expressed recombinant antigens derived from domain III of the E protein (rE-DIII) of MVEV and WNV, respectively, to determine whether these subunit antigens provided specific diagnostic markers of infection with these two viruses. When a panel of 130 serum samples, from horses with known flavivirus infection status, was tested in enzyme-linked immunosorbent assay (ELISA) using rE-DIII antigens, a differential diagnosis of MVEV or WNV was achieved for most samples. Time-point samples from horses exposed to flavivirus infection during the 2011 outbreak of equine encephalitis in south-eastern Australia also indicated that the rE-DIII antigens were capable of detecting and differentiating MVEV and WNV infection in convalescent sera with similar sensitivity and specificity to virus neutralization tests and blocking ELISAs. Overall, these results indicate that the rE-DIII is a suitable antigen for use in rapid immunoassays for confirming MVEV and WNV infections in horses in the Australian context and warrant further assessment on sensitive, high-throughput serological platforms such as multiplex immune assays.

Case Report: Zika Virus Meningoencephalitis and Myelitis and Associated Magnetic Resonance Imaging Findings

Zika virus (ZIKV) has a wide clinical spectrum of associated neurologic disease including microcephaly and Guillain-Barre syndrome but, despite its known neurotropism, ZIKV meningoencephalitis and myelitis have been rare complications. We describe a case of ZIKV meningoencephalitis and probable myelitis and its associated magnetic resonance imaging findings that rapidly resolved during recovery in a previously healthy adult.

MR imaging of adult acute infectious encephalitis

BACKGROUND

Imaging is a key tool for the diagnosis of acute encephalitis. Brain CT scan must be urgently performed to rule out a brain lesion with mass effect that would contraindicate lumbar puncture. Brain MRI is less accessible than CT scan, but can provide crucial information with patients presenting with acute encephalitis.

METHOD

We performed a literature review on PubMed on April 1, 2015 with the search terms "MRI" and "encephalitis".

RESULTS

We first described the various brain MRI abnormalities associated with each pathogen of acute encephalitis (HSV, VZV, other viral agents targeting immunocompromised patients or travelers; tuberculosis, listeriosis, other less frequent bacterial agents). Then, we identified specific patterns of brain MRI abnomalies that may suggest a particular pathogen. Limbic encephalitis is highly suggestive of HSV; it also occurs less frequently in encephalitis due to HHV6, syphillis, Whipple's disease and HIV primary infection. Rhombencephalitis is suggestive of tuberculosis and listeriosis. Acute ischemic lesions can occur in patients presenting with severe bacterial encephalitis, tuberculosis, VZV encephalitis, syphilis, and fungal infections.

CONCLUSION

Brain MRI plays a crucial role in the diagnosis of acute encephalitis. It detects brain signal changes that reinforce the clinical suspicion of encephalitis, especially when the causative agent is not identified by lumbar puncture; it can suggest a particular pathogen based on the pattern of brain abnormalities and it rules out important differential diagnosis (vascular, tumoral or inflammatory causes).

Deployable Molecular Detection of Arboviruses in the Australian Outback

The most common causes of human infection from the arboviruses that are endemic in Australia are the arthritogenic alphaviruses: Ross River virus (RRV) and Barmah Forest virus (BFV). The most serious infections are caused by the neurotropic flaviviruses, Murray Valley encephalitis virus (MVEV) and the Kunjin subtype of West Nile virus. The greatest individual risk of arbovirus infection occurs in tropical/subtropical northern Australia because of the warm, wet summer conditions from December to June, where conventional arbovirus surveillance is difficult due to a combination of low population density, large distances between population centers, poor roads, and seasonal flooding. Furthermore, virus detection requires samples to be sent to Perth up to 2,000 km away for definitive analysis, causing delays of days to weeks before test results are available and public health interventions can be started. We deployed a portable molecular biology laboratory for remote field detection of endemic arboviruses in northern Queensland, then in tropical Western Australia and detected BFV, MVEV, and RRV RNA by polymerase chain reaction (PCR) assays of extracts from mosquitoes trapped in Queensland. We then used a field-portable compact real-time thermocycler for the samples collected in the Kimberley region of Western Australia. Real-time field PCR assays enabled concurrent endemic arbovirus distribution mapping in outback Queensland and Western Australia. Our deployable laboratory method provides a concept of operations for future remote area arbovirus surveillance.

Epidemiology and outcomes of acute encephalitis

PURPOSE OF REVIEW

This review seeks to describe recent advances in the epidemiology, outcomes, and prognostic factors in acute encephalitis.

RECENT FINDINGS

Infectious causes continue to account for the largest proportion of encephalitis cases in which a cause is identified, although autoimmune causes are increasingly recognized. Type-A gamma-aminobutyric acid (GABAa) receptor antibodies have been recently identified in encephalitis with refractory seizures, whereas the roles of antibodies to the glycine receptor and dipeptidyl peptidase-like protein 6 have been defined in progressive encephalomyelitis with rigidity and myoclonus. Recent findings in the US cases of encephalomyelitis presenting with acute flaccid paralysis raise the possibility that enterovirus D68, a common respiratory pathogen, may cause central nervous system disease. Mortality from acute encephalitis occurs in about 10% of cases, with a large proportion of survivors suffering from cognitive or physical disability. In addition to delay in institution of appropriate antiviral or immune therapy, several potentially reversible factors associated with poor prognosis have been identified, including cerebral edema, status epilepticus, and thrombocytopenia.

SUMMARY

Encephalitis imposes a significant worldwide health burden and is associated with poor outcomes. Supportive treatment and early institution of therapy may improve outcomes. Careful neurocognitive assessment of survivors of encephalitis is needed to better define long-term outcomes.

Headache and Tremor: Co-occurrences and Possible Associations

BACKGROUND

Tremor and headache are two of the most prevalent neurological conditions. This review addresses possible associations between various types of tremor and headache, and provides a differential diagnosis for patients presenting with both tremor and headache.

METHODS

Data were identified by searching MEDLINE in February 2015, with the terms "tremor" and terms representing the primary headache syndromes.

RESULTS

Evidence for an association between migraine and essential tremor is conflicting. Other primary headaches are not associated with tremor. Conditions that may present with both tremor and headache include cervical dystonia, infectious diseases, hydrocephalus, spontaneous cerebrospinal fluid leaks, space-occupying lesions, and metabolic disease. Furthermore, both can be seen as a side effect of medication and in the use of recreational drugs.

DISCUSSION

No clear association between primary headaches and tremor has been found. Many conditions may feature both headache and tremor, but rarely as core clinical symptoms at presentation.

The changing epidemiology of Murray Valley encephalitis in Australia: the 2011 outbreak and a review of the literature

Murray Valley encephalitis virus (MVEV) is the most serious of the endemic arboviruses in Australia. It was responsible for six known large outbreaks of encephalitis in south-eastern Australia in the 1900s, with the last comprising 58 cases in 1974. Since then MVEV clinical cases have been largely confined to the western and central parts of northern Australia.

In 2011, high-level MVEV activity occurred in south-eastern Australia for the first time since 1974, accompanied by unusually heavy seasonal MVEV activity in northern Australia. This resulted in 17 confirmed cases of MVEV disease across Australia. Record wet season rainfall was recorded in many areas of Australia in the summer and autumn of 2011. This was associated with significant flooding and increased numbers of the mosquito vector and subsequent MVEV activity. This paper documents the outbreak and adds to our knowledge about disease outcomes, epidemiology of disease and the link between the MVEV activity and environmental factors.

Clinical and demographic information from the 17 reported cases was obtained. Cases or family members were interviewed about their activities and location during the incubation period.

In contrast to outbreaks prior to 2000, the majority of cases were non-Aboriginal adults, and almost half (40%) of the cases acquired MVEV outside their area of residence. All but two cases occurred in areas of known MVEV activity.

This outbreak continues to reflect a change in the demographic pattern of human cases of encephalitic MVEV over the last 20 years. In northern Australia, this is associated with the increasing numbers of non-Aboriginal workers and tourists living and travelling in endemic and epidemic areas, and also identifies an association with activities that lead to high mosquito exposure. This outbreak demonstrates that there is an ongoing risk of MVEV encephalitis to the heavily populated areas of south-eastern Australia.

An outbreak of Murray Valley encephalitis with 17 confirmed cases occurred across Australia in 2011. This outbreak involved parts of Australia where cases had not occurred for many decades. The epidemiology in this outbreak reflects a change that has occurred over the past 15 years, with more non-Aboriginal cases, fewer children and more cases that were not resident where they acquired the infection than had been observed prior to 2000. The outbreak was associated with significant flooding in many parts of Australia and most cases reported either outdoor activities where mosquito exposure was highly likely or significant mosquito exposure.