Climatic, High Tide and Vector Variables and the Transmission of Ross River Virus

ArticleinInternal Medicine Journal 35(11) · December 2005with 31 Reads
Abstract
This report assesses the impact of the variability in environmental and vector factors on the transmission of Ross River virus (RRV) in Brisbane, Australia. Poisson time series regression analyses were conducted using monthly data on the counts of RRV cases, climate variables (Southern Oscillation Index and rainfall), high tides and mosquito density for the period of 1998-2001. The results indicate that increases in the high tide (relative risk (RR): 1.65; 95% confidence interval (CI): 1.20-2.26), rainfall (RR: 1.45; 95% CI: 1.21-1.73), mosquito density (RR: 1.17; 95% CI: 1.09-1.27), the density of Culex annulirostris (RR: 1.25; 95% CI: 1.13-1.37) and the density of Ochlerotatus vigilax (RR: 2.39; 95% CI: 2.30-2.48), each at a lag of 1 month, were statistically significantly associated with the rise of monthly RRV incidence. The results of the present study might facilitate the development of early warning systems for reducing the incidence of this wide-spread disease in Australia and other Pacific island nations.
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  • Article
    Full-text available
    In Australia, Ross River virus (RRV) is predominantly identified and managed through passive health surveillance. Here, the proactive use of environmental datasets to improve community-scale public health interventions in southeastern Tasmania is explored. Known environmental drivers (temperature, rainfall, tide) of the RRV vector Aedes camptorhynchus are analysed against cumulative case records for five adjacent local government areas (LGAs) from 1993 to 2009. Allowing for a 0- to 3-month lag period, temperature was the most significant driver of RRV cases at 1-month lag, contributing to a 23·2% increase in cases above the long-term case average. The potential for RRV to become an emerging public health issue in Tasmania due to projected climate changes is discussed. Moreover, practical outputs from this research are proposed including the development of an early warning system for local councils to implement preventative measures, such as public outreach and mosquito spray programmes.
  • Article
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    Full-text available
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  • Article
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  • Article
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    Full-text available
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    To describe the epidemiology of Ross River virus (RRV) infection in the endemic Darwin region of tropical northern Australia and to develop a predictive model for RRV infections. Analysis of laboratory confirmed cases of RRV infection between 01 January 1991 and 30 June 2006, together with climate, tidal and mosquito data collected weekly over the study period from 11 trap sites around Darwin. The epidemiology was described, correlations with various lag times were performed, followed by Poisson modelling to determine the best main effects model to predict RRV infection. Ross River virus infection was reported equally in males and females in 1256 people over the 15.5 years. Average annual incidence was 113/100 000 people. Infections peaked in the 30-34 age-group for both sexes. Correlations revealed strong associations between monthly RRV infections and climatic variables and also each of the four implicated mosquito species populations. Three models were created to identify the best predictors of RRV infections for the Darwin area. The climate-only model included total rainfall, average daily minimum temperature and maximum tide. This model explained 44.3% deviance. Using vector-only variables, the best fit was obtained with average monthly trap numbers of Culex annulirostris, Aedes phaecasiatus, Aedes notoscriptus and Aedes vigilax. This model explained 59.5% deviance. The best global model included rainfall, minimum temperature and three mosquito species. This model explained 63.5% deviance, and predicted disease accurately. We have produced a model that accurately predicts RRV infections throughout the year, in the Darwin region. Our model also indicates that predicted anthropogenic global climatic changes may result in an increase in RRV infections. Further research needs to target other high-risk areas elsewhere in tropical Australia to ascertain the best local climatic and vector predictive RRV infection models for each region. This methodology can also be tested for assessing utility of predictive models for other mosquito-borne diseases endemic to locations outside Australia.
  • Article
    Full-text available
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  • Article
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    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.
  • Article
    Australia has a diversity of vectors and vector-borne human diseases. Mosquito-borne arboviruses are of greatest concern, but there are issues with other vector and pathogen systems. Mosquitoes were responsible for more than 35,000 cases of Ross River virus during 1991-1997. Barmah Forest virus is increasing nationwide, and unidentified bunyaviruses suspected of causing illness have been isolated. Cases of Murray Valley encephalitis have occurred in 14 of the past 20 years in northern Australia. Dengue is a continuing problem for northern Queensland, with various serotypes being active. Japanese encephalitis has appeared in the Torres Strait Islands and threatens mainland Australia. Although malaria is eradicated, almost 1,000 cases are imported annually and occasional cases of local transmission occur. With ticks, paralysis in children occurs annually in eastern Australia. Tick typhus (Queensland Tick Typhus--Rickettsia australis) occurs down the east coast, and (Flinders Island Spotted Fever--Rickettsia honei) in Bass Strait and probably Tasmania. Lyme disease is reported but its presence is controversial. Fleas were responsible for a recent outbreak of murine typhus (Rickettsia typhi) in Western Australia. Mites cause scrub typhus (Orientia tsutsugamushi), and there was a recent fatality in the Northern Territory. Overall, resources for investigation and control of vector-borne disease have generally been meager. However, various avenues of basic and applied research have been pursued, and have included investigations into mosquito ecology, vector competence, disease epidemiology, and vector control. Disease surveillance programs vary between states, and mosquito control programs are organized and effective in only a few regions. There are concerns for import of vectors such as Aedes albopictus and export of pathogens such as Ross River virus; the former has occurred but the species has not become established, and the latter has occurred and has resulted in a major outbreak in the South Pacific. The predicted scenarios of increased temperature and rainfall with global warming are also causing concern for increases in vector-borne diseases, particularly the endemic arboviruses. Interest by health authorities is gravitating more towards epidemiological reporting and less towards public health action. In many respects, humans have much to do to get 'on top' of vectors and their pathogens 'down under' in Australia.
  • Article
    Recent El Niño events have stimulated interest in the development of modeling techniques to forecast extremes of climate and related health events. Previous studies have documented associations between specific climate variables (particularly temperature and rainfall) and outbreaks of arboviral disease. In some countries, such diseases are sensitive to El Niño. Here we describe a climate-based model for the prediction of Ross River virus epidemics in Australia. From a literature search and data on case notifications, we determined in which years there were epidemics of Ross River virus in southern Australia between 1928 and 1998. Predictor variables were monthly Southern Oscillation index values for the year of an epidemic or lagged by 1 year. We found that in southeastern states, epidemic years were well predicted by monthly Southern Oscillation index values in January and September in the previous year. The model forecasts that there is a high probability of epidemic Ross River virus in the southern states of Australia in 1999. We conclude that epidemics of arboviral disease can, at least in principle, be predicted on the basis of climate relationships. Images Figure 1
  • Article
    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 (rs=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.
  • Article
    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. 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. 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. 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.
  • Article
    Full-text available
    This paper describes the development of an empirical model to forecast epidemics of Ross River virus (RRV) disease using the multivariate seasonal auto-regressive integrated moving average (SARIMA) technique in Brisbane, Australia. We obtained computerized data on notified RRV disease cases, climate, high tide, and population sizes in Brisbane for the period 1985-2001 from the Queensland Department of Health, the Australian Bureau of Meteorology, the Queensland Department of Transport, and Australian Bureau of Statistics, respectively. The SARIMA model was developed and validated by dividing the data file into two data sets: the data between January 1985 and December 2000 were used to construct a model, and those between January and December 2001 to validate it. The SARIMA models show that monthly precipitation (beta = 0.004, P = 0.031) was significantly associated with RRV transmission. However, there was no significant association between other climate variables (e.g., temperature, relative humidity, and high tides) and RRV transmission. The predictive values in the model were generally consistent with actual values (root mean square percentage error = 0.94%). Therefore, this model may have applications as a decision supportive tool in disease control and risk-management planning programs.
  • Article
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    To describe the natural history of rheumatic manifestations of Ross River virus (RRV) disease. Prospective longitudinal clinical review. North Queensland local government areas of Cairns, Douglas, Mareeba and Atherton during January to May 1998. General practice patients diagnosed with RRV disease on the basis of symptoms and a positive RRV IgM result. Rheumatic symptoms and signs assessed as soon as possible after disease onset and on two subsequent occasions (up to 6.5 months after onset). 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. Earlier studies may have overestimated the prevalence and duration of symptoms in RRV disease. Progressive resolution over 3-6 months appears usual.
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    Full-text available
    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. 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. 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. 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.
  • Article
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    There have been 5 confirmed cases of Murray Valley encephalitis virus (MVE) infection in the Alice Springs region during the high rainfall years of 1999/00 and 2000/01, compared with one case in the preceding 9 years. There also appeared to be an increased prevalence of Ross River virus (RR) infection in the Alice Springs and Tennant Creek regions associated with high rainfall. This paper presents an analysis of summer rainfall from 1990/91 to 2000/01, numbers of seroconversion of sentinel chickens to MVE, and RR cases in both regions. In Alice Springs where summer rainfall (December to February) and average vector numbers in the December to March period are closely correlated, the analysis also included mosquito vector numbers and MVE cases. Summer rainfall over 100 mm was significantly associated with sentinel chicken seroconversions to MVE. From December to March there was also a significant association of average vector numbers (> or = 300) with seroconversions in sentinel chickens following high summer rainfall. MVE appears enzootic in the Tennant Creek region and epizootic in the Alice Springs region. In Alice Springs during December to March, there was a significant association of RR cases with rainfall over 100 mm and with average vector numbers over 300. There was also a significant correlation of summer rainfall with RR cases in Tennant Creek. Summer rainfall is a new and good early indicator of high risk for both MVE and RR disease in the Alice Springs locality and RR in the Tennant Creek locality. Although similar relationships between rainfall and vector abundance, and disease incidence probably exist in other areas of central Australia, rainfall and vector abundance thresholds will probably vary according to local climatic and environmental conditions.
  • Article
    El Niño Southern Oscillation (ENSO) is a climate event that originates in the Pacific Ocean but has wide-ranging consequences for weather around the world, and is especially associated with droughts and floods. The irregular occurrence of El Niño and La Niña events has implications for public health. On a global scale, the human effect of natural disasters increases during El Niño. The effect of ENSO on cholera risk in Bangladesh, and malaria epidemics in parts of South Asia and South America has been well established. The strongest evidence for an association between ENSO and disease is provided by time-series analysis with data series that include more than one event. Evidence for ENSO's effect on other mosquito-borne and rodent-borne diseases is weaker than that for malaria and cholera. Health planners are used to dealing with spatial risk concepts but have little experience with temporal risk management. ENSO and seasonal climate forecasts might offer the opportunity to target scarce resources for epidemic control and disaster preparedness.
  • Article
    How climate variability affects the transmission of infectious diseases at a regional level remains unclear. We assess the impact of climate variation on the Ross River virus (RRv) transmission in the Townsville region, Queensland, north-east Australia. We obtained population-based information on monthly variations in RRv cases, climatic factors, sea level, and population growth between 1985 and 1996. Cross-correlations were computed for a series of associations 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. We assessed the impact of climate variability on RRv transmission using the seasonal auto-regressive integrated moving average (SARIMA) model. There were significant correlations of the monthly incidence of RRv to rainfall, maximum temperature, minimum temperature and relative humidity, all at a lag of 2 months, and high tide in the current month. The results of SARIMA models show that monthly average rainfall (beta = 0.0007, P = 0.01) and high tide (beta = 0.0089, P = 0.04) were significantly associated with RRv transmission and maximum temperature was also marginally significantly associated with monthly incidence of RRv (beta = 0.0412, P = 0.07), although relative humidity did not seem to have played an important role in the Townsville region. Rainfall, high tide and maximum temperature were likely to be key determinants of RRv transmission in the Townsville region.
  • Article
    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.