Arbovirus infection in a Murray Valley community

Seroprevalence of Japanese encephalitis virus-specific antibodies in Australia following novel epidemic spread: protocol for a national cross-sectional study

INTRODUCTION

Japanese encephalitis virus (JEV) is a mosquito-borne flavivirus that causes encephalitis and other morbidity in Southeast Asia. Since February 2022, geographically dispersed JEV human, animal and vector detections occurred on the Australian mainland for the first time. This study will determine the prevalence of JEV-specific antibodies in human blood with a focus on populations at high risk of JEV exposure and determine risk factors associated with JEV seropositivity by location, age, occupation and other factors.

METHOD

Samples are collected using two approaches: from routine blood donors (4153 samples), and active collections targeting high-risk populations (convenience sampling). Consent-based sampling for the latter includes a participant questionnaire on demographic, vaccination and exposure data. Samples are tested for JEV-specific total antibody using a defined epitope-blocking ELISA, and total antibody to Australian endemic flaviviruses Murray Valley encephalitis and Kunjin viruses.

ANALYSIS

Two analytic approaches will occur: descriptive estimates of seroprevalence and multivariable logistic regression using Bayesian hierarchical models. Descriptive analyses will include unadjusted analysis of raw data with exclusions for JEV-endemic country of birth, travel to JEV-endemic countries, prior JEV-vaccination, and sex-standardised and age-standardised analyses. Multivariable logistic regression will determine which risk factors are associated with JEV seropositivity likely due to recent transmission within Australia and the relative contribution of each factor when accounting for effects within the model.

ETHICS

National Mutual Acceptance ethical approval was obtained from the Sydney Children's Hospitals Network Human Research Ethics Committee (HREC). Local approvals were sought in each jurisdiction. Ethical approval was also obtained from the Australian Red Cross Lifeblood HREC.

DISSEMINATION

Findings will be communicated to participants and their communities, and human and animal health stakeholders and policy-makers iteratively and after final analyses. Understanding human infection rates will inform procurement and targeted allocation of limited JEV vaccine, and public health strategies and communication campaigns, to at-risk populations.

Human Seroprevalence for Dengue, Ross River, and Barmah Forest viruses in Australia and the Pacific: A systematic review spanning seven decades

Background

Dengue (DENV), Ross River (RRV) and Barmah Forest viruses (BFV) are the most common human arboviral infections in Australia and the Pacific Island Countries and Territories (PICTs) and are associated with debilitating symptoms. All are nationally notifiable in Australia, but routine surveillance is limited to a few locations in the PICTs. Understanding the level of human exposure to these viruses can inform disease management and mitigation strategies. To assess the historic and current seroprevalence of DENV, RRV and BFV in Australia and the PICTs we conducted a systematic literature review of all published quantitative serosurveys.

Methodology and principal findings

The Preferred Reporting of Items for Systematic Reviews and Meta-Analyses procedures were adopted to produce a protocol to systematically search for published studies reporting the seroprevalence of DENV, RRV and BFV in Australia and the PICTs. Data for author, research year, location, study population, serosurvey methods and positive tests were extracted. A total of 41 papers, reporting 78 serosurveys of DENV, RRV and BFV including 62,327 samples met the inclusion criteria for this review. Seroprevalence varied depending on the assay used, strategy of sample collection and location of the study population. Significant differences were observed in reported seropositivity depending on the sample collection strategy with clinically targeted sampling reporting the highest seroprevalence across all three viruses. Non-stratified seroprevalence showed wide ranges in reported positivity with DENV 0.0% – 95.6%, RRV 0.0% – 100.0%, and BFV 0.3% – 12.5%. We discuss some of the causes of variation including serological methods used, selection bias in sample collection including clinical or environmental associations, and location of study site. We consider the extent to which serosurveys reflect the epidemiology of the viruses and provide broad recommendations regarding the conduct and reporting of arbovirus serosurveys.

Conclusions and significance

Human serosurveys provide important information on the extent of human exposure to arboviruses across: (1) time, (2) place, and (3) person (e.g., age, gender, clinical presentation etc). Interpreting results obtained at these scales has the potential to inform us about transmission cycles, improve diagnostic surveillance, and mitigate future outbreaks. Future research should streamline methods and reduce bias to allow a better understanding of the burden of these diseases and the factors associated with seroprevalence. Greater consideration should be given to the interpretation of seroprevalence in studies, and increased rigour applied in linking seroprevalence to transmission dynamics.

Low seroprevalence of Murray Valley encephalitis and Kunjin viruses in an opportunistic serosurvey, Victoria 2011

OBJECTIVE

To assess evidence of recent and past exposure to Murray Valley encephalitis virus (MVEV) and West Nile clade Kunjin virus (KUNV) in residents of the Murray Valley, Victoria, during a period of demonstrated activity of both viruses in early 2011.

METHODS

A cross-sectional serosurvey using two convenience samples: stored serum specimens from a diagnostic laboratory in Mildura and blood donors from the Murray Valley region. Specimens were collected between April and July 2011. The main outcome measure was total antibody (IgM and IgG) reactivity against MVEV and KUNV measured using an enzyme immunoassay and defined as inhibiting binding of monoclonal antibodies by >50%, when compared to negative controls. Evidence of recent exposure was measured by the presence of MVEV and KUNV IgM detected by immunofluorescence.

RESULTS

Of 1,115 specimens, 24 (2.2%, 95% CI 1.3-3.0%) were positive for MVEV total antibody, and all were negative for MVEV IgM. Of 1,116 specimens, 34 (3.1%, 95% CI 2.0-4.0%) were positive for KUNV total antibody, and 3 (0.27%) were KUNV IgM positive. Total antibody seroprevalence for both viruses was higher in residents born before 1974.

CONCLUSIONS

Despite widespread MVEV and KUNV activity in early 2011, this study found that seroprevalence of antibodies to both viruses was low (<5%) and little evidence of recent exposure.

IMPLICATIONS

Our findings suggest both viruses remain epizootic in the region and local residents remain potentially susceptible to future outbreaks.

Influence of hosts on the ecology of arboviral transmission: potential mechanisms influencing dengue, Murray Valley encephalitis, and Ross River virus in Australia

Ecological interactions are fundamental to the transmission of infectious disease. Arboviruses are particularly elegant examples, where rich arrays of mechanisms influence transmission between vectors and hosts. Research on host contributions to the ecology of arboviral diseases has been undertaken within multiple subdisciplines, but significant gaps in knowledge remain and multidisciplinary approaches are needed. Through our multidisciplinary review of the literature we have identified five broad areas where hosts may influence the ecology of arboviral transmission: host immunity; cross-protective immunity and antibody-dependent enhancement; host abundance; host diversity; and pathogen spillover and dispersal. Herein we discuss the known and theoretical roles of hosts within these topics and then apply this knowledge to three epidemiologically important mosquito-borne arboviruses that occur in Australia: dengue virus (DENV), Murray Valley encephalitis virus (MVEV), and Ross River virus (RRV). We argue that the underlying mechanisms by which hosts influence arboviral activity are numerous and attempts to delineate these mechanisms further are needed. Investigations that focus on hosts of vector-borne diseases are likely to be rewarding, particularly where the ecology of vectors is relatively well understood. From an applied perspective, enhanced knowledge of host influences upon vector-borne disease transmission is likely to enable better management of disease burden. Finally, we suggest a framework that may be useful to identify and determine host contributions to the ecology of arboviruses.

The risk of Ross River and Barmah Forest virus disease in Queensland: implications for New Zealand

OBJECTIVES

To describe the incidence of Ross River (RR) and Barmah Forest (BF) virus disease in Queensland and determine the risk of importation of RR virus from Queensland into New Zealand (NZ) via viraemic travellers.

METHODS

Based on routine RR and BF virus notification data of seven major urban tropical and subtropical Queensland populations, incidence rates adjusted for age, sex, season and a baseline level of immunity were used to examine the annual and seasonal risk of disease in the specific populations and selected subgroups. The risk for NZ was determined by estimating the number of infections among major visitor groups travelling from Queensland to NZ, using seroconversion rates.

RESULTS

In Queensland, annual rates of RR and BF virus disease ranged between 31.5-288.3 and 3.4-37.4/100,000 person years respectively and increased to between 48.4-423.5 and 3.8-40.4/100,000 person years at risk when adjusted for immunity. Our estimates indicate that more than 100 viraemic travellers may enter NZ from Queensland each year. Estimates were greatest among New Zealanders returning home.

CONCLUSIONS AND IMPLICATIONS

Usefulness of notification data could be maximised by presenting more detailed information to the local governments responsible for the control and public health awareness of these pathogens. Given the high number of viraemic persons entering NZ, the abundance of possums and the emergence of Oc. camptorhynchus, transmission of RR virus within NZ is probable. Health authorities should prepare for a virgin soil epidemic of RR virus by initiating serological and clinical surveillance in key areas, enhance public and professional awareness and elevate national resources necessary to invoke emergency vector control and case management.

Ross River virus infection on the North Coast of New South Wales

A retrospective follow-up survey was undertaken of residents of the North Coast of New South Wales infected with Ross River virus in 1992. The aims of the study were to describe the epidemiology and acute symptomatology of Ross River virus infection, its natural history during the first 12 months of infection, and its effects on those infected. Questionnaires were distributed to both cases and their medical practitioners. Of 129 people infected, aged between six and 85 years, 81 (63 per cent) were male and 48 (37 per cent) were female. The peak age-specific incidence was in the age group 50 to 59 years. The most common symptoms were arthralgia (95 per cent) and tiredness (91 per cent). Over 60 per cent took time off work. At 12 months follow-up, over 50 per cent reported persistent arthralgia, 35 per cent reported persistent tiredness and 15 per cent were still unable to carry out their normal activities. The median duration of symptoms was in the range 7 to 12 months, and of incapacity was in the range five weeks to three months. There were some differences from previous reports of Ross River virus outbreaks, in the incidence of major symptoms and the duration of illness and incapacity. These are likely to be at least partly due to inconsistent measurement methods. In this study, there were systematic differences between medical practitioners' and patients' estimates of periods of incapacity. Previous estimates of the direct economic costs and indirect human costs of infection based on data obtained from medical practitioners, although alarming, are almost certainly underestimates.