Changing epidemiology of Ross River virus disease in South Australia

Exposure dynamics of Ross River virus in horses - Horses as potential sentinels (a One Health approach)

Ross River virus (RRV), the most medically and economically important arbovirus in Australia, has been the most prevalent arbovirus infections in humans for many years. Infected humans and horses often suffer similar clinical symptoms. We conducted a prospective longitudinal study over a 3.5-year period to investigate the exposure dynamics of RRV in three foal cohorts (n = 32) born in a subtropical region of South East Queensland, Australia, between 2020 and 2022. RRV-specific seroconversion was detected in 56% (n = 18) of foals with a median time to seroconversion, after waning of maternal antibodies, of 429 days (95% CI: 294-582). The median age at seroconversion was 69 weeks (95% CI: 53-57). Seroconversion events were only detected between December and March (Southern Hemisphere summer) over the entire study period. Cox proportion hazards regression analyses revealed that seroconversions were significantly (p < 0.05) associated with air temperature in the month of seroconversion. Time-lags in meteorological variables were not significantly (p > 0.05) associated with seroconversion, except for relative humidity (p = 0.036 at 2-month time-lag). This is in contrast to research results of RRV infection in humans, which peaked between March and May (Autumn) and with a 0-3 month time-lag for various meteorological risk factors. Therefore, horses may be suitable sentinels for monitoring active arbovirus circulation and could be used for early arbovirus outbreak detection in human populations.

Implications of Innate Immunity in Post-Acute Sequelae of Non-Persistent Viral Infections

Non-persistent viruses classically cause transient, acute infections triggering immune responses aimed at the elimination of the pathogen. Successful viruses evolved strategies to manipulate and evade these anti-viral defenses. Symptoms during the acute phase are often linked to dysregulated immune responses that disappear once the patient recovers. In some patients, however, symptoms persist or new symptoms emerge beyond the acute phase. Conditions resulting from previous transient infection are termed post-acute sequelae (PAS) and were reported for a wide range of non-persistent viruses such as rota-, influenza- or polioviruses. Here we provide an overview of non-persistent viral pathogens reported to be associated with diverse PAS, among them chronic fatigue, auto-immune disorders, or neurological complications and highlight known mechanistic details. Recently, the emergence of post-acute sequelae of COVID-19 (PASC) or long COVID highlighted the impact of PAS. Notably, PAS of non-persistent infections often resemble symptoms of persistent viral infections, defined by chronic inflammation. Inflammation maintained after the acute phase may be a key driver of PAS of non-persistent viruses. Therefore, we explore current insights into aberrant activation of innate immune signaling pathways in the post-acute phase of non-persistent viruses. Finally, conclusions are drawn and future perspectives for treatment and prevention of PAS are discussed.

Ross River Virus Infection: A Cross-Disciplinary Review with a Veterinary Perspective

Ross River virus (RRV) has recently been suggested to be a potential emerging infectious disease worldwide. RRV infection remains the most common human arboviral disease in Australia, with a yearly estimated economic cost of $4.3 billion. Infection in humans and horses can cause chronic, long-term debilitating arthritogenic illnesses. However, current knowledge of immunopathogenesis remains to be elucidated and is mainly inferred from a murine model that only partially resembles clinical signs and pathology in human and horses. The epidemiology of RRV transmission is complex and multifactorial and is further complicated by climate change, making predictive models difficult to design. Establishing an equine model for RRV may allow better characterization of RRV disease pathogenesis and immunology in humans and horses, and could potentially be used for other infectious diseases. While there are no approved therapeutics or registered vaccines to treat or prevent RRV infection, clinical trials of various potential drugs and vaccines are currently underway. In the future, the RRV disease dynamic is likely to shift into temperate areas of Australia with longer active months of infection. Here, we (1) review the current knowledge of RRV infection, epidemiology, diagnostics, and therapeutics in both humans and horses; (2) identify and discuss major research gaps that warrant further research.

Spatial and temporal patterns of Ross River virus in south east Queensland, Australia: identification of hot spots at the rural-urban interface

Background

Ross River virus (RRV) is responsible for the most common vector-borne disease of humans reported in Australia. The virus circulates in enzootic cycles between multiple species of mosquitoes, wildlife reservoir hosts and humans. Public health concern about RRV is increasing due to rising incidence rates in Australian urban centres, along with increased circulation in Pacific Island countries. Australia experienced its largest recorded outbreak of 9544 cases in 2015, with the majority reported from south east Queensland (SEQ). This study examined potential links between disease patterns and transmission pathways of RRV.

Methods

The spatial and temporal distribution of notified RRV cases, and associated epidemiological features in SEQ, were analysed for the period 2001–2016. This included fine-scale analysis of disease patterns across the suburbs of the capital city of Brisbane, and those of 8 adjacent Local Government Areas, and host spot analyses to identify locations with significantly high incidence.

Results

The mean annual incidence rate for the region was 41/100,000 with a consistent seasonal peak in cases between February and May. The highest RRV incidence was in adults aged from 30 to 64 years (mean incidence rate: 59/100,000), and females had higher incidence rates than males (mean incidence rates: 44/100,000 and 34/100,000, respectively). Spatial patterns of disease were heterogeneous between years, and there was a wide distribution of disease across both urban and rural areas of SEQ. Overall, the highest incidence rates were reported from predominantly rural suburbs to the north of Brisbane City, with significant hot spots located in peri-urban suburbs where residential, agricultural and conserved natural land use types intersect.

Conclusions

Although RRV is endemic across all of SEQ, transmission is most concentrated in areas where urban and peri-urban environments intersect. The drivers of RRV transmission across rural-urban landscapes should be prioritised for further investigation, including identification of specific vectors and hosts that mediate human spillover.

Flooding and Arboviral Disease: Predicting Ross River Virus Disease Outbreaks Across Inland Regions of South-Eastern Australia

Flood frequency is expected to increase across the globe with climate change. Understanding the relationship between flooding and arboviral disease can reduce disease risk and associated costs. South-eastern Australia is dominated by the flood-prone Murray-Darling River system where the incidence of Australia's most common arboviral disease, Ross River virus (RRV), is high. This study aimed to determine the relationship between riverine flooding and RRV disease outbreaks in inland south-eastern Australia, specifically New South Wales (NSW). Each study month from 1991 to 2013, for each of 37 local government areas (LGAs) was assigned 'outbreak/non-outbreak' status based on long-term trimmed-average age-standardized RRV notification rates and 'flood/non-flood' status based on riverine overflow. LGAs were grouped into eight climate zones with the relationship between flood and RRV outbreak modeled using generalized estimating equations. Modeling adjusted for rainfall in the previous 1-3 mo. Spring-summer flooding increased the odds of summer RRV outbreaks in three climate zones before and after adjusting for rainfall 1, 2, and 3 mo prior to the outbreak. Flooding at any time of the year was not predictive of RRV outbreaks in the remaining five climate zones. Predicting RRV disease outbreaks with flood events can assist with more targeted mosquito spraying programs, thereby reducing disease transmission and mosquito resistance.

Chronic viral infections in myalgic encephalomyelitis/chronic fatigue syndrome (ME/CFS)

Background and main text

Myalgic encephalomyelitis/chronic fatigue syndrome (ME/CFS) is a complex and controversial clinical condition without having established causative factors. Increasing numbers of cases during past decade have created awareness among patients as well as healthcare professionals. Chronic viral infection as a cause of ME/CFS has long been debated. However, lack of large studies involving well-designed patient groups and validated experimental set ups have hindered our knowledge about this disease. Moreover, recent developments regarding molecular mechanism of pathogenesis of various infectious agents cast doubts over validity of several of the past studies.

Conclusions

This review aims to compile all the studies done so far to investigate various viral agents that could be associated with ME/CFS. Furthermore, we suggest strategies to better design future studies on the role of viral infections in ME/CFS.

Improving public health intervention for mosquito-borne disease: the value of geovisualization using source of infection and LandScan data

Epidemiological studies use georeferenced health data to identify disease clusters but the accuracy of this georeferencing is obfuscated by incorrectly assigning the source of infection and by aggregating case data to larger geographical areas. Often, place of residence (residence) is used as a proxy for the source of infection (source) which may not be accurate. Using a 21-year dataset from South Australia of human infections with the mosquito-borne Ross River virus, we found that 37% of cases were believed to have been acquired away from home. We constructed two risk maps using age-standardized morbidity ratios (SMRs) calculated using residence and patient-reported source. Both maps confirm significant inter-suburb variation in SMRs. Areas frequently named as the source (but not residence) and the highest-risk suburbs both tend to be tourist locations with vector mosquito habitat, and camping or outdoor recreational opportunities. We suggest the highest-risk suburbs as places to focus on for disease control measures. We also use a novel application of ambient population data (LandScan) to improve the interpretation of these risk maps and propose how this approach can aid in implementing disease abatement measures on a smaller scale than for which disease data are available.

Genetic ablation of arginase 1 in macrophages and neutrophils enhances clearance of an arthritogenic alphavirus

Chikungunya virus (CHIKV) and Ross River virus (RRV) cause a debilitating, and often chronic, musculoskeletal inflammatory disease in humans. Macrophages constitute the major inflammatory infiltrates in musculoskeletal tissues during these infections. However, the precise macrophage effector functions that affect the pathogenesis of arthritogenic alphaviruses have not been defined. We hypothesized that the severe damage to musculoskeletal tissues observed in RRV- or CHIKV-infected mice would promote a wound-healing response characterized by M2-like macrophages. Indeed, we found that RRV- and CHIKV-induced musculoskeletal inflammatory lesions, and macrophages present in these lesions, have a unique gene-expression pattern characterized by high expression of arginase 1 and Ym1/Chi3l3 in the absence of FIZZ1/Relmα that is consistent with an M2-like activation phenotype. Strikingly, mice specifically deleted for arginase 1 in neutrophils and macrophages had dramatically reduced viral loads and improved pathology in musculoskeletal tissues at late times post-RRV infection. These findings indicate that arthritogenic alphavirus infection drives a unique myeloid cell activation program in inflamed musculoskeletal tissues that inhibits virus clearance and impedes disease resolution in an arginase 1-dependent manner.

Bayesian spatiotemporal analysis of socio-ecologic drivers of Ross River virus transmission in Queensland, Australia

This study aims to examine the impact of socio-ecologic factors on the transmission of Ross River virus (RRV) infection and to identify areas prone to social and ecologic-driven epidemics in Queensland, Australia. We used a Bayesian spatiotemporal conditional autoregressive model to quantify the relationship between monthly variation of RRV incidence and socio-ecologic factors and to determine spatiotemporal patterns. Our results show that the average increase in monthly RRV incidence was 2.4% (95% credible interval (CrI): 0.1-4.5%) and 2.0% (95% CrI: 1.6-2.3%) for a 1 degrees C increase in monthly average maximum temperature and a 10 mm increase in monthly average rainfall, respectively. A significant spatiotemporal variation and interactive effect between temperature and rainfall on RRV incidence were found. No association between Socio-economic Index for Areas (SEIFA) and RRV was observed. The transmission of RRV in Queensland, Australia appeared to be primarily driven by ecologic variables rather than social factors.

Arthritis and arthralgia three years after Sindbis virus infection: clinical follow-up of a cohort of 49 patients

Sindbis virus (SINV) emerges as large human outbreaks in northern Europe every 7 years. Similar to many other alphaviruses, SINV is a mosquito-borne causative agent of a rash-arthritis. Previous reports suggest that in many alphavirus infections joint symptoms might persist for years. A prospective cohort of 49 patients was physically examined 3 y after verified acute SINV infection to reveal persistent joint symptoms. We carefully searched for a temporal association between the infection and current symptoms, and took into account other medical conditions. Sera were collected and analysed with enzyme immunoassays. Arthritis (swelling and tenderness on physical examination) was diagnosed in 4.1% (2/49) of the patients. Tenderness on palpation or in movement of a joint was found in 14.3% of the patients in the rheumatological examination, and an additional 10.2% complained of persisting arthralgia at the interview. Thus, 24.5% of the patients had joint manifestations attributable to the infection 3 y earlier. A positive IgM antibody response persisted in 3/49 of the patients; both patients with arthritis were in this group. As one-quarter of the patients were symptomatic 3 y after infection, it seems that persistent symptoms of SINV infection have considerable public health implications in areas with high seroprevalence.

Genome microevolution of chikungunya viruses causing the Indian Ocean outbreak

BACKGROUND

A chikungunya virus outbreak of unprecedented magnitude is currently ongoing in Indian Ocean territories. In Réunion Island, this alphavirus has already infected about one-third of the human population. The main clinical symptom of the disease is a painful and invalidating poly-arthralgia. Besides the arthralgic form, 123 patients with a confirmed chikungunya infection have developed severe clinical signs, i.e., neurological signs or fulminant hepatitis.

METHODS AND FINDINGS

We report the nearly complete genome sequence of six selected viral isolates (isolated from five sera and one cerebrospinal fluid), along with partial sequences of glycoprotein E1 from a total of 127 patients from Réunion, Seychelles, Mauritius, Madagascar, and Mayotte islands. Our results indicate that the outbreak was initiated by a strain related to East-African isolates, from which viral variants have evolved following a traceable microevolution history. Unique molecular features of the outbreak isolates were identified. Notably, in the region coding for the non-structural proteins, ten amino acid changes were found, four of which were located in alphavirus-conserved positions of nsP2 (which contains helicase, protease, and RNA triphosphatase activities) and of the polymerase nsP4. The sole isolate obtained from the cerebrospinal fluid showed unique changes in nsP1 (T301I), nsP2 (Y642N), and nsP3 (E460 deletion), not obtained from isolates from sera. In the structural proteins region, two noteworthy changes (A226V and D284E) were observed in the membrane fusion glycoprotein E1. Homology 3D modelling allowed mapping of these two changes to regions that are important for membrane fusion and virion assembly. Change E1-A226V was absent in the initial strains but was observed in >90% of subsequent viral sequences from Réunion, denoting evolutionary success possibly due to adaptation to the mosquito vector.

CONCLUSIONS

The unique molecular features of the analyzed Indian Ocean isolates of chikungunya virus demonstrate their high evolutionary potential and suggest possible clues for understanding the atypical magnitude and virulence of this outbreak.

Ross River virus: Molecular and cellular aspects of disease pathogenesis

Ross River virus (RRV) is a mosquito-borne alphavirus indigenous to Australia and the Western Pacific region and is responsible for several thousand cases of human RRV disease (RRVD) per annum. The disease primarily involves polyarthritis/arthralgia, with many patients also presenting with rash, myalgia, fever, and/or lethargy. The symptoms can be debilitating at onset, but they usually resolve within 3-6 months. Recent insights into the RRV-host relationship, associated pathology, and molecular biology of infection have generated a number of potential avenues for improved treatment. Although vaccine development has been proposed, the small market size and potential for antibody-dependent enhancement (ADE) of disease make this approach unattractive. Recent insights into the molecular basis of RRV-ADE and the virus's ability to manipulate host inflammatory and immune responses create potential new opportunities for therapeutic invention. Such interventions should overcome virus-induced dysregulation of protective host responses to promote viral clearance and/or ameliorate inflammatory immunopathology.

Sindbis viruses and other alphaviruses as cause of human arthritic disease

Amongst the arthritis-causing arboviruses, i.e. those spread by insects, the alphavirus group is of special interest. These viruses occasionally cause vast outbreaks, such as O'nyong-nyong in Africa in 1959. In Fennoscandia, Sindbis-related Ockelbo, Pogosta, or Karelian fever viruses have been found to cause significant morbidity. The major symptoms in addition to joint inflammation are fever, fatigue, headache and rash. The joint symptoms may persist for weeks, even months. The diagnosis is based on the clinical picture and serology. The causative viruses are closely related but not identical. It appears that at least in Finland the Pogosta disease is more common than thought, and the symptoms may often be overlooked. Several factors related to the viruses, their hosts, and global environmental changes may affect the spread of these viruses. All over the world arbovirus-caused diseases have increased, because of global changes.

Using human disease outbreaks as a guide to multilevel ecosystem interventions

Human health often depends on environmental variables and is generally subject to widespread and comprehensive surveillance. Compared with other available measures of ecosystem health, human disease incidence may be one of the most useful and practical bioindicators for the often elusive gauge of ecologic well-being. We argue that many subtle ecosystem disruptions are often identified only as a result of detailed epidemiologic investigations after an anomalous increase in human disease incidence detected by routine surveillance mechanisms. Incidence rates for vector-mediated diseases (e.g., arboviral illnesses) and direct zoonoses (e.g., hantaviruses) are particularly appropriate as bioindicators to identify underlying ecosystem disturbances. Outbreak data not only have the potential to act as a pivotal warning system for ecosystem disruption, but may also be used to identify interventions for the preservation of ecologic health. With this approach, appropriate ecologically based strategies for remediation can be introduced at an earlier stage than would be possible based solely on environmental monitoring, thereby reducing the level of "ecosystem distress" as well as resultant disease burden in humans. This concept is discussed using local, regional, and global examples, thereby introducing the concept of multilevel ecosystem interventions. Key words: bioindicators, disease control, disease outbreaks, ecologic management, ecosystem health, surveillance.

Ross River virus disease in Australia: epidemiology, socioecology and public health response

Societal and ecosystem change have a potentially profound impact of on human health and well-being. Alteration in the pattern of infectious diseases could be one of the most significant results of this process. Arboviral infections are a global public health issue with significant morbidity and mortality burden in the human population. Ross River virus (RRV) infection is the most common arboviral disease in Australia and some Pacific island nations. The present paper aims to illustrate the epidemiological and socioecological implications of RRV infection in Australia and to make recommendations for public health response to this disease.

Ross River virus disease in Australia, 1886-1998, with analysis of risk factors associated with outbreaks

Ross River virus (RR) is a mosquito-borne arbovirus responsible for outbreaks of polyarthritic disease throughout Australia. To better understand human and environmental factors driving such events, 57 historical reports on RR outbreaks between 1896 and 1998 were examined collectively. The magnitude, regularity, seasonality, and locality of outbreaks were found to be wide ranging; however, analysis of climatic and tidal data highlighted that environmental conditions act differently in tropical, arid, and temperate regions. Overall, rainfall seems to be the single most important risk factor, with over 90% of major outbreak locations receiving higher than average rainfall in preceding months. Many temperatures were close to average, particularly in tropical populations; however, in arid regions, below average maximum temperatures predominated, and in southeast temperate regions, above average minimum temperatures predominated. High spring tides preceded coastal outbreaks, both in the presence and absence of rainfall, and the relationship between rainfall and the Southern Oscillation Index and La Niña episodes suggest they may be useful predictive tools, but only in southeast temperate regions. Such heterogeneity predisposing outbreaks supports the notion that there are different RR epidemiologies throughout Australia but also suggests that generic parameters for the prediction and control of outbreaks are of limited use at a local level.

Ross River virus disease in tropical Queensland: evolution of rheumatic manifestations in an inception cohort followed for six months

OBJECTIVE

To describe the natural history of rheumatic manifestations of Ross River virus (RRV) disease.

DESIGN

Prospective longitudinal clinical review.

SETTING

North Queensland local government areas of Cairns, Douglas, Mareeba and Atherton during January to May 1998.

PARTICIPANTS

General practice patients diagnosed with RRV disease on the basis of symptoms and a positive RRV IgM result.

MAIN OUTCOME MEASURES

Rheumatic symptoms and signs assessed as soon as possible after disease onset and on two subsequent occasions (up to 6.5 months after onset).

RESULTS

57 patients were recruited, 47 of whom were reviewed three times (at means of 1.1, 2.4 and 3.6 months after disease onset). Results are reported for these 47: 46 (98%) complained of joint pain at first review, with the ankles, wrists, fingers, knees and metacarpophalangeal joints (II-IV) most commonly involved. Prevalence of joint pain decreased progressively on second and third reviews, both overall (92% and 68% of patients, respectively), and in the five joints most commonly affected. The prevalence of other common rheumatic symptoms and signs, and use of non-steroidal anti-inflammatory drugs, also progressively declined over the three reviews.

CONCLUSIONS

Earlier studies may have overestimated the prevalence and duration of symptoms in RRV disease. Progressive resolution over 3-6 months appears usual.

Natural history of Ross River virus-induced epidemic polyarthritis

OBJECTIVE

To describe the natural history, treatment and cost of Ross River virus-induced epidemic polyarthritis (RRV disease).

DESIGN

Questionnaire-based longitudinal prospective study.

PARTICIPANTS AND SETTING

Patients in the greater Brisbane area, Queensland, diagnosed with RRV disease by their general practitioners based on clinical symptoms and paired serological tests between November 1997 and April 1999.

MAIN OUTCOME MEASURES

Scores on two validated quality-of-life questionnaires (Clinical Health Assessment Questionnaire and Medical Outcomes Study Short Form 36) were obtained soon after diagnosis and one, two, three, six and 12 months thereafter. Scores were compared between patients diagnosed with RRV disease alone and those with RRV disease plus other conditions.

RESULTS

67 patients were enrolled. Most patients with RRV disease alone had severe acute symptoms, but followed a consistent path to recovery within three to six months. Other conditions, often chronic rheumatic diseases or depression, were identified in half the cohort; their quality-of-life scores suggested stable chronic illness between six and 12 months after diagnosis. Non-steroidal anti-inflammatory drugs (NSAIDs) were taken by 58% of patients (average use, 7.6 weeks; range, 2-22 weeks). Time off work averaged 1.9 days, and direct cost to the community was estimated as 1018 Australian dollars per patient.

CONCLUSIONS

Symptom duration and frequency of long-term symptoms may have been overestimated by previous studies of RRV disease. Disease persisting six to 12 months after RRV diagnosis was largely attributable to other conditions, highlighting the need to seek other diagnoses in RRV patients with persistent symptoms.

Climate variability and Ross River virus transmission

OBJECTIVES

(1) To examine the feasibility to link climate data with monthly incidence of Ross River virus (RRv). (2) To assess the impact of climate variability on the RRv transmission.

DESIGN

An ecological time series analysis was performed on the data collected between 1985 to 1996 in Queensland, Australia.

METHODS

Information on the notified RRv cases was obtained from the Queensland Department of Health. Climate and population data were supplied by the Australian Bureau of Meteorology and the Australian Bureau of Statistics, respectively. Spearman's rank correlation analyses were performed to examine the relation between climate variability and the monthly incidence of notified RRv infections. The autoregressive integrated moving average (ARIMA) model was used to perform a time series analysis. As maximum and minimum temperatures were highly correlated with each other (r(s)=0.75), two separate models were developed.

RESULTS

For the eight major cities in Queensland, the climate-RRv correlation coefficients were in the range of 0.12 to 0.52 for maximum and minimum temperatures, -0.10 to 0.46 for rainfall, and 0.11 to 0.52 for relative humidity and high tide. For the whole State, rainfall (partial regression coefficient: 0.017 (95% confidence intervals 0.009 to 0.025) in Model I and 0.018 (0.010 to 0.026) in Model II), and high tidal level (0.030 (0.006 to 0.054) in Model I and 0.029 (0.005 to 0.053) in Model II) seemed to have played significant parts in the transmission of RRv in Queensland. Maximum temperature was also marginally significantly associated with the incidence of RRv infection.

CONCLUSION

Rainfall, temperature, and tidal levels may be important environmental determinants in the transmission cycles of RRv disease.

Ross River virus: ecology and distribution

Ross River virus is the most common mosquito-borne pathogen in Australia, and approximately 5000 human cases are reported annually. The infection is not fatal, but there is considerable morbidity associated with a debilitating polyarthritis that is the major symptom. The virus is annually active in most regions of Australia, but exists as strains that vary in virulence. Native macropods are thought to be the natural vertebrate hosts, although horses and humans may be involved during epidemic activity, and vertical transmission of the virus occurs in mosquitoes. Different mosquito species are involved as vectors in various regions and in different seasonal and environmental conditions. In coastal areas the saltmarsh mosquitoes Aedes camptorhynchus and Ae. vigilax are the most important vectors in southern and northern regions, respectively, whereas in inland areas Culex annulirostris is the most important vector, although various Aedes species can be involved depending on region and conditions, and the epidemiology of the disease and vector control imperatives vary with circumstance concomitantly.

Ross River virus transmission, infection, and disease: a cross-disciplinary review

Ross River virus (RRV) is a fascinating, important arbovirus that is endemic and enzootic in Australia and Papua New Guinea and was epidemic in the South Pacific in 1979 and 1980. Infection with RRV may cause disease in humans, typically presenting as peripheral polyarthralgia or arthritis, sometimes with fever and rash. RRV disease notifications in Australia average 5,000 per year. The first well-described outbreak occurred in 1928. During World War II there were more outbreaks, and the name epidemic polyarthritis was applied. During a 1956 outbreak, epidemic polyarthritis was linked serologically to a group A arbovirus (Alphavirus). The virus was subsequently isolated from Aedes vigilax mosquitoes in 1963 and then from epidemic polyarthritis patients. We review the literature on the evolutionary biology of RRV, immune response to infection, pathogenesis, serologic diagnosis, disease manifestations, the extraordinary variety of vertebrate hosts, mosquito vectors, and transmission cycles, antibody prevalence, epidemiology of asymptomatic and symptomatic human infection, infection risks, and public health impact. RRV arthritis is due to joint infection, and treatment is currently based on empirical anti-inflammatory regimens. Further research on pathogenesis may improve understanding of the natural history of this disease and lead to new treatment strategies. The burden of morbidity is considerable, and the virus could spread to other countries. To justify and design preventive programs, we need accurate data on economic costs and better understanding of transmission and behavioral and environmental risks.

Arboviruses associated with human disease in Australia

Mosquito-borne arboviruses are an important public health issue in Australia. The alphaviruses Ross River and Barmah Forest virus are widespread and active annually, and cause debilitating polyarthritis. The flaviviruses Murray Valley encephalitis, Kunjin and Japanese encephalitis virus are restricted in distribution and activity but may cause life-threatening illness, and dengue viruses are active in some areas.

A comparison of the diseases caused by Ross River virus and Barmah Forest virus

Barmah Forest virus (BFV) and Ross River virus (RRV) are mosquito-borne viruses with similar vectors and environmental requirements. They cause diseases characterised by arthralgia, arthritis and myalgia, often accompanied by fever and rash. Arthritis is more common and more prominent in RRV disease and rash is more common and florid with BFV infection, although the diseases cannot be reliably distinguished by their clinical symptoms. Diagnosis is based on serological tests and a definite diagnosis of recent infection requires the demonstration of rising titres of IgG. Arthralgia, myalgia and lethargy may continue for at least six months in up to half of patients with RRV, but in only about 10% of patients with BFV. Both diseases are managed symptomatically.

Mosquito-borne arboviruses in Australia: the current scene and implications of climate change for human health

Of the mosquito-borne arboviruses, the encephalitic Murray Valley encephalitis and Kunjin viruses are a major public health concern, but the arthritides Ross River and Barmah Forest viruses are more important in a public health sense, being responsible for a far greater number of infections. Reported cases of Ross River totalled approximately 30,000 during 1991-1996; there have been several widely separated outbreaks of Barmah Forest in recent years and case reports are increasing annually. Surveillance programmes have increased our understanding of the geographic regions, climatic conditions and vector factors associated with viruses. Virus activity is widespread but is often localised, is driven primarily by mosquito abundance and various species are involved; host factors are involved also, but are not well understood. Typically, mosquito populations are governed by availability of habitat and environmental conditions. Models of climate change predict increases in rainfall, tides and temperature for parts of Australia, and such changes have the potential to increase the risk of arbovirus transmission by increasing the distribution and abundance of vectors, and duration of mosquito and arbovirus seasons. However, the amplitude of climate change is uncertain and the ecology of arbovirus transmission is complex. It is likely that some areas will have increases in arbovirus activity and human infection with predicted climate change, but risk of increased transmission will vary with locality, vector, host and human factors.

The relationship between fatigue, psychological and immunological variables in acute infectious illness

OBJECTIVE

The aim of this paper is to explore the longitudinal relationships between physical and psychological symptoms and immunological factors following acute infective illnesses.

METHOD

Preliminary data from a prospective investigation of patients with serologically proven acute infectious illnesses due to Epstein-Barr virus (EBV), Ross River virus (RRV) or Q fever are reported. Patients were assessed within 4 weeks of onset of symptoms and then reviewed 2 and 4 weeks later. Physical illness data were collected at interview. Psychological and somatic symptom profiles were assessed by standardised self-report questionnaires. Cell-mediated immune (CMI) function was assessed by measurement of delayed-type hypersensitivity (DTH) skin responses.

RESULTS

Thirty patients who had been assessed and followed over the 4-week period (including 17 patients with EBV, five with RRV and eight with Q fever) were included in this analysis. During the acute phase, profound fatigue and malaise were the most common symptoms. Classical depressive and anxiety symptoms were not prominent. Initially, 46% of cases had no DTH skin response (i.e. cutaneous anergy) indicative of impaired cellular immunity. Over the 4-week period, there was a marked improvement in both somatic and psychological symptoms, although fatigue remained a prominent feature in 63% of subjects. The reduction in reported fatigue was correlated with improvement in the DTH skin response (p = 0.001) and with improvement in General Health Questionnaire (GHQ) scores (p < 0.01).

CONCLUSIONS

Acute infectious illnesses are accompanied by a range of nonspecific somatic and psychological symptoms, particularly fatigue and malaise rather than anxiety and depression. Although improvement in several symptoms occurs rapidly, fatigue commonly remains a prominent complaint at 4 weeks. Resolution of fatigue is associated with improvement in cell-mediated immunity.