A major outbreak of epidemic polyarthritis in New South Wales during the summer of 1983/1984

Gastro-oesophageal reflux disease

Gastro-oesophageal reflux disease (GERD) is a common disorder in adults and children. The global prevalence of GERD is high and increasing. Non-erosive reflux disease is the most common phenotype of GERD. Heartburn and regurgitation are considered classic symptoms but GERD may present with various atypical and extra-oesophageal manifestations. The pathophysiology of GERD is multifactorial and different mechanisms may result in GERD symptoms, including gastric composition and motility, anti-reflux barrier, refluxate characteristics, clearance mechanisms, mucosal integrity and symptom perception. In clinical practice, the diagnosis of GERD is commonly established on the basis of response to anti-reflux treatment; however, a more accurate diagnosis requires testing that includes upper gastrointestinal tract endoscopy and reflux monitoring. New techniques and new reflux testing parameters help to better phenotype the condition. In children, the diagnosis of GERD is primarily based on history and physical examination and treatment vary with age. Treatment in adults includes a combination of lifestyle modifications with pharmacological, endoscopic or surgical intervention. In refractory GERD, optimization of proton-pump inhibitor treatment should be attempted before a series of diagnostic tests to assess the patient's phenotype.

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.

Infection of Western Gray Kangaroos (Macropus fuliginosus) with Australian Arboviruses Associated with Human Infection

More than 75 arboviruses (arthropod-borne viruses) have been identified in Australia. While Alfuy virus (ALFV), Barmah Forest virus (BFV), Edge Hill virus (EHV), Kokobera virus (KOKV), Murray Valley encephalitis virus (MVEV), Sindbis virus (SINV), Ross River virus (RRV), Stratford virus (STRV), and West Nile virus strain Kunjin (KUNV) have been associated with human infection, there remains a paucity of data regarding their respective transmission cycles and any potential nonhuman vertebrate hosts. It is likely that these viruses are maintained in zoonotic cycles involving native animals rather than solely by human-to-human transmission. A serosurvey (n = 100) was undertaken to determine the prevalence of neutralizing antibodies against a panel of Australian arboviruses in western gray kangaroos (Macropus fuliginosus) obtained from 11 locations in the midwest to southwest of Western Australia. Neutralizing antibodies against RRV were detected in 25%, against BFV in 14%, and antibodies to both viruses in 34% of serum samples. The prevalence of antibodies against these two viruses was the same in males and females, but higher in adult than in subadult kangaroos (p < 0.05). Twenty-one percent of samples had neutralizing antibodies against any one or more of the flaviviruses ALFV, EHV, KOKV, MVEV, and STRV. No neutralizing antibodies against SINV and KUNV were detected. If this sample of kangaroo sera was representative of the broader Australian population of macropods, it suggests that they are common hosts for RRV and BFV. The absence or low seroprevalence of antibodies against the remaining arboviruses suggests that they are not prevalent in the region or that kangaroos are not commonly infected with them. The detection of neutralizing antibodies to MVEV requires further investigation as this virus has not been identified previously so far south in Western Australia.

Arthritogenic Alphaviruses: A Worldwide Emerging Threat?

Arthritogenic alphaviruses are responsible for a dengue-like syndrome associated with severe debilitating polyarthralgia that can persist for months or years and impact life quality. Chikungunya virus is the most well-known member of this family since it was responsible for two worldwide epidemics with millions of cases in the last 15 years. However, other arthritogenic alphaviruses that are as of yet restrained to specific territories are the cause of neglected tropical diseases: O'nyong'nyong virus in Sub-Saharan Africa, Mayaro virus in Latin America, and Ross River virus in Australia and the Pacific island countries and territories. This review evaluates their emerging potential in light of the current knowledge for each of them and in comparison to chikungunya virus.

Ross River virus disease clinical presentation, pathogenesis and current therapeutic strategies

Ross River virus (RRV) is an arthitogenic alphavirus capable of causing outbreaks of debilitating musculoskeletal inflammatory disease in humans. RRV is the most common mosquito-borne disease in Australia, with outbreaks of RRV generally occurring during seasonal wet and warm conditions. Patients with Ross River virus disease (RRVD) typically present with fever, polyarthralgia, myalgia and a maculopapular erythematous rash. Treatment of the disease is usually palliative with no licensed vaccines or antiviral therapies currently available. In an effort to better inform therapeutic design, much progress has been made to understand the pathogenesis of RRVD. Progress has been largely driven by clinical evaluations supported by research using established murine models of RRVD, able to accurately replicate human disease. In this review we describe RRVD pathogenesis and the role of the host immune response, with particular focus on insights from studying animal models. We also discuss prospects for effective vaccines, preclinical development of therapeutic strategies and raise important questions for future RRV research.

Analysis of Arbovirus Isolates from Australia Identifies Novel Bunyaviruses Including a Mapputta Group Virus from Western Australia That Links Gan Gan and Maprik Viruses

The Mapputta group comprises antigenically related viruses indigenous to Australia and Papua New Guinea that are included in the family Bunyaviridae but not currently assigned to a specific genus. We determined and analyzed the genome sequences of five Australian viruses isolated from mosquitoes collected during routine arbovirus surveillance in Western Australia (K10441, SW27571, K13190, and K42904) and New South Wales (12005). Based on matching sequences of all three genome segments to prototype MRM3630 of Trubanaman virus (TRUV), NB6057 of Gan Gan virus (GGV), and MK7532 of Maprik virus (MPKV), isolates K13190 and SW27571 were identified as TRUV, 12005 as GGV, and K42904 as a Mapputta group virus from Western Australia linking GGV and MPKV. The results confirmed serum neutralization data that had linked SW27571 to TRUV. The fifth virus, K10441 from Willare, was most closely related to Batai orthobunyavirus, presumably representing an Australian variant of the virus. Phylogenetic analysis also confirmed the close relationship of our TRUV and GGV isolates to two other recently described Australian viruses, Murrumbidgee virus and Salt Ash virus, respectively. Our findings indicate that TRUV has a wide circulation throughout the Australian continent, demonstrating for the first time its presence in Western Australia. Similarly, the presence of a virus related to GGV, which had been linked to human disease and previously known only from the Australian southeast, was demonstrated in Western Australia. Finally, a Batai virus isolate was identified in Western Australia. The expanding availability of genomic sequence for novel Australian bunyavirus variants supports the identification of suitably conserved or diverse primer-binding target regions to establish group-wide as well as virus-specific nucleic acid tests in support of specific diagnostic and surveillance efforts throughout Australasia.

Analysis and prediction of Ross River virus transmission in New South Wales, Australia

BACKGROUND

Ross River virus (RRV) disease is the most widespread mosquito-borne disease in Australia. The disease is maintained in enzootic cycles between mosquitoes and reservoir hosts. During outbreaks and in endemic regions, RRV transmission can be sustained between vectors and reservoir hosts in zoonotic cycles with spillover to humans. Symptoms include arthritis, rash, fever and fatigue and can persist for several months. The prevalence and associated morbidity make this disease a medically and economically important mosquito-borne disease in Australia.

METHODS

Climate, environment, and RRV vector and reservoir host information were used to develop predictive models in four regions in NSW over a 13-year period (1991-2004). Polynomial distributed lag (PDL) models were used to explore long-term influences of up to 2 years ago that could be related to RRV activity.

RESULTS

Each regional model consisted of a unique combination of predictors for RRV disease highlighting the differences in the disease ecology and epidemiology in New South Wales (NSW). Events up to 2 years before were found to influence RRV activity. The shorter-term associations may reflect conditions that promote virus amplification in RRV vectors whereas long-term associations may reflect RRV reservoir host breeding and herd immunity. The models indicate an association between host populations and RRV disease, lagged by 24 months, suggesting two or more generations of susceptible juveniles may be necessary for an outbreak. Model sensitivities ranged from 60.4% to 73.1%, and model specificities ranged from 57.9% to 90.7%. This was the first study to include reservoir host data into statistical RRV models; the inclusion of host parameters was found to improve model fit significantly.

CONCLUSION

The research presents the novel use of a combination of climate, environment, and RRV vector and reservoir host information in statistical predictive models. The models have potential for public health decision-making.

Projecting the impact of climate change on the transmission of Ross River virus: methodological challenges and research needs

Ross River virus (RRV) is the most common vector-borne disease in Australia. It is vitally important to make appropriate projections on the future spread of RRV under various climate change scenarios because such information is essential for policy-makers to identify vulnerable communities and to better manage RRV epidemics. However, there are many methodological challenges in projecting the impact of climate change on the transmission of RRV disease. This study critically examined the methodological issues and proposed possible solutions. A literature search was conducted between January and October 2012, using the electronic databases Medline, Web of Science and PubMed. Nineteen relevant papers were identified. These studies demonstrate that key challenges for projecting future climate change on RRV disease include: (1) a complex ecology (e.g. many mosquito vectors, immunity, heterogeneous in both time and space); (2) unclear interactions between social and environmental factors; and (3) uncertainty in climate change modelling and socioeconomic development scenarios. Future risk assessments of climate change will ultimately need to better understand the ecology of RRV disease and to integrate climate change scenarios with local socioeconomic and environmental factors, in order to develop effective adaptation strategies to prevent or reduce RRV transmission.

Climate variability, social and environmental factors, and ross river virus transmission: research development and future research needs

BACKGROUND

Arbovirus diseases have emerged as a global public health concern. However, the impact of climatic, social, and environmental variability on the transmission of arbovirus diseases remains to be determined.

OBJECTIVE

Our goal for this study was to provide an overview of research development and future research directions about the interrelationship between climate variability, social and environmental factors, and the transmission of Ross River virus (RRV), the most common and widespread arbovirus disease in Australia.

METHODS

We conducted a systematic literature search on climatic, social, and environmental factors and RRV disease. Potentially relevant studies were identified from a series of electronic searches.

RESULTS

The body of evidence revealed that the transmission cycles of RRV disease appear to be sensitive to climate and tidal variability. Rainfall, temperature, and high tides were among major determinants of the transmission of RRV disease at the macro level. However, the nature and magnitude of the interrelationship between climate variability, mosquito density, and the transmission of RRV disease varied with geographic area and socioenvironmental condition. Projected anthropogenic global climatic change may result in an increase in RRV infections, and the key determinants of RRV transmission we have identified here may be useful in the development of an early warning system.

CONCLUSIONS

The analysis indicates that there is a complex relationship between climate variability, social and environmental factors, and RRV transmission. Different strategies may be needed for the control and prevention of RRV disease at different levels. These research findings could be used as an additional tool to support decision making in disease control/surveillance and risk management.

Detection of Ross River virus in clinical samples using a nested reverse transcription-polymerase chain reaction

BACKGROUND

Ross River virus (RRV) is a mosquito borne alphavirus that has been found in Australia, Papua New Guinea and the Pacific Islands. It is aetiological agent of epidemic polyarthritis, a debilitating illness whose symptoms are arthritis, arthralgia, lethargy, rash and fever which may persist for weeks or months. Diagnosis is made on a serological basis, but in many cases is presumptive rather than definite.

OBJECTIVES

To apply the polymerase chain reaction (PCR) to detection of RRV in human sera to assess its suitability for application in disease diagnosis.

STUDY DESIGN

Sensitivity of the nested RT-PCR assay was determined by detection of virus of known titre diluted in uninfected serum. Clinical serum samples from patients serologically diagnosed of having RRV infection were tested by nested RT-PCR to assess its diagnostic value.

RESULTS

Sensitivity of the nested RT-PCR assay was determined to be detection of 0.01 PFU of virus stock in 100 mul serum. Clinical samples tested showed that 10 of 26 (38%) serum samples with low or negative (non-diagnostic) virus-specific antibody titres were PCR-positive, whereas all 22 specimens with high antibody titres were PCR-negative. PCR positivity was unaffected by repeated freezing and thawing of samples.

CONCLUSIONS

While PCR cannot replace serology as a means of RRV diagnosis, it may be useful in conjunction with serological testing, particularly for forming definitive diagnoses in those samples with low (inconclusive) antibody titres. It is faster and more sensitive than virus isolation by tissue culture, and could also prove useful in investigations of disease pathogenesis.

Acute symptoms and sequelae of Ross River virus infection in South-Western Australia: a follow-up study

BACKGROUND

Unusually high tides along the south-west coast of Western Australia (WA) during the spring and summer of 1988-89 provided ideal breeding conditions for mosquito vectors of Ross River virus (RRV). This was followed by the biggest outbreak of RRV infection ever documented in WA (330 notified cases).

OBJECTIVES

To describe the nature and duration of symptoms of RRV infection in WA, and associated functional disability; to determine the perceived effectiveness of treatments; to determine the usefulness of available information on RRV infection.

STUDY DESIGN

A retrospective study of all cases of RRV infection reported from South West WA during the 1988-89 outbreak, using a self-administered patient questionnaire.

RESULTS

The most common symptoms were arthralgia, tiredness and lethargy, and joint stiffness and swelling. In patients with joint manifestations, the knees, wrists and ankles were almost always affected. Non-steroidal anti-inflammatory agents, rest, simple analgesics and hydrotherapy were subjectively the most helpful treatments. Only 27% of patients had recovered completely within 6 months of onset of symptoms. Three years after the outbreak, up to 57% still experienced at least intermittent joint symptoms. Less than one-third of people reported that the available information adequately explained the consequences of RRV infection.

CONCLUSIONS

Compared with patients elsewhere in Australia, people infected with RRV in the South West of WA experience a slightly different spectrum of clinical symptoms, with a longer period of disability. This may be related to the presence of a different topotype of the virus to that found elsewhere in Australia. Better information for doctors and patients on the likely course of the illness is needed. Future studies should examine the economic cost associated with RRV infection, and evaluate treatments to shorten the period of disability.

Specific enzyme immunoassays for the rapid detection of Ross River virus in cell cultures inoculated with infected mosquito homogenates

BACKGROUND

Ross River (RR) virus is a mosquito-borne alphavirus and one of the aetiological agents of epidemic polyarthritis in humans. Early detection of increased virus activity in mosquito populations enables public health authorities to implement measures to reduce the number of human infections during epidemics. However, current surveillance techniques require a minimum of four weeks for viruses to be isolated and identified.

OBJECTIVES

This study was carried out to assess the use of enzyme immunoassays (EIA) as rapid alternatives to traditional cell culture techniques for detection of RR virus in mosquitoes.

STUDY DESIGN

Enzyme immunoassays and immunoperoxidase assays were developed using RR-specific monoclonal antibodies and compared to traditional methods for detection of RR virus in field-caught mosquito samples.

RESULTS

By inoculation of C6/36 cell cultures with mosquito homogenates and testing monolayers and culture supernatant by EIA, RR virus was detected and identified in all infected samples within 6 days.

CONCLUSIONS

The use of EIA provides a rapid, sensitive and specific alternative to traditional methods for the detection of RR virus in mosquito vectors.

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.

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.

Different responses of Ross River virus to climate variability between coastline and inland cities in Queensland, Australia

AIMS

To examine the potential impact of climate variability on the transmission of Ross River virus (RRv) infection, and to assess the difference in the potential predictors of RRv incidence in coastline and inland regions, Queensland, Australia.

METHODS

Information on the RRv cases notified between 1985 to 1996 was obtained from the Queensland Department of Health. Climate and population data were supplied by the Australian Bureau of Meteorology and the Australia Bureau of Statistics, respectively. The function of cross correlations was used to compute a series of correlations between climate variables (rainfall, maximum temperature, minimum temperature, relative humidity, and high tide) and the monthly incidence of RRv disease over a range of time lags. Time series Poisson regression models were performed to adjust for the autocorrelations of the monthly incidences of RRv disease and the confounding effects of seasonality, the case notification time, and population sizes.

RESULTS

The cross correlation function shows rainfall, maximum temperature, minimum temperature, and relative humidity at a lag of 1-2 months and high tide in the current month were significantly associated with the monthly incidence of RRv in the coastline region. Relative humidity and rainfall at a lag of two months was also significantly associated with the monthly incidence of RRv in the inland region. The results of Poisson regressive models show that the incidence of RRv disease was significantly associated with rainfall, maximum temperature, minimum temperature, relative humidity, and high tide in the coastline region, and with rainfall and relative humidity in the inland region. There was a significant interaction between climate variables and locality in RRv transmission.

CONCLUSIONS

Climate variability may have played a significant role in the transmission of RRv. There appeared to be different responses of RRv to climate variability between coastline and inland cities in Queensland, Australia. Maximum temperature appeared to exhibit a greater impact on the RRv transmission in coastline than in inland cities. Minimum temperature and relative humidity at 3 pm inland seemed to affect the RRv transmission more than at the coastline. However, the relation between climate variables and RRv needs to be viewed within a wider context of other social and environmental factors, and further research is needed.

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.

Persistent Ross River virus infection of murine macrophages: an in vitro model for the study of viral relapse and immune modulation during long-term infection

A clinical feature of Ross River virus disease (RRVD) is the periodic relapse of symptoms months after the initial onset of disease. The underlying mechanisms responsible for this relapse have not been determined. In a long-term (148 days) in vitro study of persistently infected murine macrophages we established that RRV infection periodically fell to undetectable biological levels that required genetic detection. However, the virus concentration spontaneously relapsed to biologically detectable levels that corresponded with enhanced viral mRNA expression, cellular detachment, and cytopathic effect. By altering the cell culture conditions we found that relapse could also be induced. We propose that the periodic relapse of symptoms in RRVD may be associated with spontaneous or stress-induced increases in RRV within persistently infected macrophages. This study also established that RRV enhanced macrophage phagocytic activity and dysregulated the immunoregulatory molecules CD80, IFN-gamma, and TNF-alpha that may facilitate persistence of RRV and avoidance of immune responses.

Predicting Ross River virus epidemics from regional weather data

BACKGROUND

Diseases caused by arboviruses cause extensive mortality and morbidity throughout the world. Weather directly affects the breeding, abundance, and survival of mosquitoes, the principal vector of many arboviruses. The goal of this study was to test whether climate variables could predict with high levels of accuracy (more than 70%) epidemics of one arbovirus, Ross River virus disease.

METHODS

Weather data from two regions in southeastern Australia were matched with Ross River virus disease data for the period 1991 to 1999. Our aim was to develop simple models for the probability of the occurrence of an epidemic in an area in a given year.

RESULTS

Two predictable epidemic patterns emerged, after either high summer rainfalls or high winter rainfalls. A prerequisite relating to host-virus dynamics was lower than average spring rainfall in the preepidemic year. The sensitivity of the model was 96% for Region 1 and 73% for Region 2.

CONCLUSIONS

Early warning of weather conditions conducive to outbreaks of Ross River virus disease is possible at the regional level with a high degree of accuracy. Our models may have application as a decision tool for health authorities to use in risk-management planning.

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: 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.

Changing epidemiology of Ross River virus disease in South Australia

OBJECTIVE

To investigate changes in epidemiology and symptoms of Ross River virus (RRV) disease in South Australia.

DESIGN

Longitudinal questionnaire-based survey of notified cases from one to 36 months after infection.

SUBJECTS

All patients with recent serologically confirmed RRV infection notified to the Communicable Disease Control Unit, South Australian Health Commission, between 1 October 1992 and 30 June 1993.

OUTCOME MEASURES

Sociodemographic data, source of infection, symptoms and ability to carry out daily activities (at onset of illness and at time of questionnaire, up to 36 months after infection), symptom duration, economic impact of the illness, cases recovery time, factors predictive of delayed recovery.

RESULTS

Information was obtained on the acute illness from 698 of the 821 subjects and at 15 months after infection from 436. At 15 months, 51% of respondents still had joint pain and 45% had persistent tiredness and lethargy. Other common symptoms included myalgia (34%), lymphadenopathy (25%), headache (23%) and depression (22%). These symptoms were still common 30 months after infection. Increasing age was the only statistically significant predictor of delayed recovery. Infections were acquired across the State, away from previously recognised RRV-endemic areas.

CONCLUSIONS

For many people, RRV disease is debilitating, with long term symptoms similar to those of chronic fatigue syndrome. The geographic range of the infection has expanded in SA.

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.

Mosquito-borne viruses and epidemic polyarthritis

The two most common mosquito-borne viruses associated with epidemic polyarthritis and polyarticular disease are Ross River and Barmah Forest viruses, accounting for about 90% and 10%, respectively, of serologically confirmed cases. Occasional cases of polyarticular disease in Australia have been associated with infection by other mosquito-borne arboviruses, but the role of these viruses in human disease remains to be confirmed.

Climate change and global infectious disease threats

The world's climate is warming up and, while debate continues about how much change we can expect, it is becoming clear that even small changes in climate can have major effects on the spread of disease. Erwin K Jackson, a member of Greenpeace International's Climate Impacts Unit and a delegate to the 11th session of the United Nations Intergovernmental Panel on Climate Change (Rome, 11-15 December), reviews the scientific evidence of this new global threat to health.

Arboviruses causing human disease in the Australasian zoogeographic region

Over 65 arboviruses have been reported from countries in the Australasian zoogeographic region, but only a few have been implicated in human disease. These include the flaviviruses Murray Valley encephalitis (MVE), Kunjin (KUN), Kokobera (KOK), and dengue, particularly types 1 and 2; the alphaviruses Ross River (RR), Barmah Forest (BF), and Sindbis (SIN); and the bunyaviruses, Gan Gan and Trubanaman. In this paper recent epidemiological and clinical results pertaining to these viruses are reviewed, with major emphasis on MVE and RR viruses. The extensive early studies of Australian arboviruses have been reviewed by Doherty [49, 50], and their ecology and vectors more recently by Kay and Standfast [87]. In addition, the biology of MVE and KUN [113] and RR [87, 114] viruses have been the subjects of more detailed reviews. The Australasian zoogeographic region is defined as countries east of the Wallace and Weber lines, two hypothetical lines in the Indo-Australian archipelago where the fauna of the Australasian and Oriental regions meet. Seroepidemiological studies of human arboviral infections have suggested that the Japanese encephalitis flavivirus and the chikungunya alphavirus occur only in the Oriental region, whereas the related MVE and RR viruses, respectively, are restricted to the Australasian region [85, 148]. Serological results from Wallacea, the zone between the Wallace and Weber lines, are not so clear-cut [85]. This review is therefore restricted to countries east of Wallacea, specifically New Guinea and Australia.

Arbovirus infections of humans in high-risk areas of south-eastern Australia: a continuing study

OBJECTIVES

To determine the current immune status of high-risk populations of New South Wales and Victoria to the arboviral pathogens, Murray Valley encephalitis (MVE) and Kunjin (KUN) viruses, which are associated with Australian encephalitis (AE), and Ross River (RR) and Kokobera (KOK) viruses which are associated with polyarthritis. Further, to estimate seroconversion rates to these viruses in high-risk populations over the 10-year period 1981-1991.

DESIGN AND STUDY POPULATION

Blood was taken from 2873 permanent residents, children and adults from previously identified high-risk areas in western NSW and northern Victoria. Samples were tested by the haemagglutination-inhibition (HI) test for antibodies to the four viruses. All sera were also tested for MVE and KUN antibodies by the more specific neutralisation test (NT). Ninety-five of the subjects had been seronegative when sampled 10 years previously.

RESULTS

Age standardised prevalence rates for flavivirus HI antibodies (MVE, KUN, KOK) ranged from 66% (Bourke) to 15% (Forbes), and were similar to those observed 10 years previously. However, specific NT antibodies to MVE and KUN were uncommon in all districts except Bourke, indicating a very high level of susceptibility to Australian encephalitis, should a fresh epidemic occur. Whereas KUN virus seems enzootic in NSW and Victoria, MVE did not appear to have been present since the last outbreak in 1974, even in Bourke. Flavivirus antibody rates (as detected by the broadly reactive HI test) greatly exceeded those specifically attributable to MVE and KUN (NT test) or KOK, leading to the speculation that unidentified flaviviruses are responsible for most human infections. Ross River virus antibody prevalence rates exceeded those of flaviviruses in all districts, ranging from 72% (Bourke) to 25% (Cohuna), and were uniformly higher than those observed in 1981. Ten-year seroconversion rates in seronegative panels were 8.5% for flaviviruses and 24.2% for RR virus, and are broadly consistent with the cross-sectional study.

CONCLUSIONS

Although flavivirus and alphavirus infections have occurred at a "steady rate"in western NSW and northern Victoria, there is a general lack of immunity to the agents of Australian encephalitis in all centres except Bourke. This needs to be considered in public health policy in these areas.

Illness caused by a Barmah Forest-like virus in New South Wales

Barmah Forest virus, a recently-discovered arbovirus which belongs to the alphavirus genus of the family Togaviridae, has been shown to cause infections in humans in New South Wales. The present report documents three patients in whom Barmah Forest viral infection appears to have resulted in illness. Barmah Forest virus or a closely-related alphavirus may, as are several other alphaviruses, be pathogenic.