Malaria in a changing world: an Australian perspective

Malaria research in Australia: looking through the lens of the past towards the future

Malaria remains a global health priority, with substantial resources devoted to control and intervention since the causative parasite was first identified in 1880. Major advances have been made in discovery and translational research activities aimed at prevention, treatment and control. Laboratory-based, clinical, and field-based studies have complemented public health approaches. Australian scientists have played important roles, developing and applying innovative approaches, novel research tools and cutting-edge technologies in animal and human models of disease, as well as in disease-endemic settings. This article will provide an insight into 50 years of Australian efforts to discover mechanisms and targets of immunity and pathogenesis; develop new diagnostics, drugs, vaccines, and therapeutics; and assess new public health interventions and control measures in malaria-endemic settings.

Climate change and infectious diseases in Australia: future prospects, adaptation options, and research priorities

Climate change will have significant and diverse impacts on human health. These impacts will include changes in infectious disease incidence. In this article, the authors review the current situation and potential future climate change impacts for respiratory, diarrheal, and vector-borne diseases in Australia. Based on this review, the authors suggest adaptive strategies within the health sector and also recommend future research priorities.

Meteorological variables and malaria in a Chinese temperate city: A twenty-year time-series data analysis

OBJECTIVES

This study aimed to examine the impact of climate variation on malaria in a temperate region of China.

METHODS

A 20-year historical time-series data analysis was conducted to examine the relationship between meteorological variables, including maximum and minimum temperatures, rainfall, humidity, and cases of malaria in Jinan, a temperate city in northern China. Data were retrieved from 1959 and 1979 and analyzed on a monthly basis. Spearman correlation and cross-correlation analyses were performed to identify time lag values between each meteorological variable and the number of malaria cases. The Seasonal Autoregressive Integrated Moving Average (SARIMA) model was used to quantify the relationship between the meteorological variables and malaria cases.

RESULTS

The SARIMA models indicate that a 1 degrees C rise in maximum temperature may be related to a 7.7% to 12.7% increase and a 1 degrees C rise in minimum temperature may result in approximately 11.8% to 15.8% increase in the number of malaria cases. A clear association between malaria and other selected weather variables, including rainfall and humidity, has not been detected in this study.

CONCLUSIONS

Temperature could play an important role in the transmission of malaria in temperate regions of China.

Climate change and the transmission of vector-borne diseases: a review

This article reviews studies examining the relationship between climate variability and the transmission of vector- and rodent-borne diseases, including malaria, dengue fever, Ross River virus infection, and hemorrhagic fever with renal syndrome. The review has evaluated their study designs, statistical analysis methods, usage of meteorological variables, and results of those studies. The authors found that the limitations of analytical methods exist in most of the articles. Besides climatic variables, few of them have included other factors that can affect the transmission of vector-borne disease (eg, socioeconomic status). In addition, the quantitative relationship between climate and vector-borne diseases is inconsistent. Further research should be conducted among different populations with various climatic/ecological regions by using appropriate statistical models.

A comparison of two generic trap types for monitoring mosquitoes through an annual cycle in tropical Australia

We compare the community composition, abundance, and seasonality of mosquito species detected by the encephalitis virus surveillance (EVS) CO2 traps and Centers for Disease Control and Prevention (CDC) light traps. Traps were run concurrently for a year during routine weekly monitoring in the vicinity of the city of Darwin in northern Australia. The EVS CO2 traps detected far more individuals than CDC light traps notwithstanding a weaker suction fan, but species richness was similar. Regardless of variation in community composition among sites, differences between trap types were remarkably consistent. Seasonal trends in the abundance of 5 key species from each trap type were similar, but markedly more so in strongly seasonal species. Although EVS CO2 traps outperformed CDC light traps for routine monitoring, the historical transition from the latter to the former is unlikely to have major consequences for the identification of community composition or detection of seasonal trends in key species.

Is there a risk of malaria transmission in NSW?

NSW has a putative malaria vector in Anopheles annulipes, and increased numbers of immigrants from malaria endemic countries who may be infective to mosquitoes but asymptomatic. We examine the factors known to influence malaria transmission and conclude that local transmission is possible but unlikely. The public health implications are that there should be systematic screening of immigrants from malaria endemic countries on arrival, and that the public health capacity to identify and respond to a malaria outbreak should be maintained.

An outbreak of Plasmodium vivax malaria in Far North Queensland, 2002

OBJECTIVE

To describe an outbreak of Plasmodium vivax malaria in Far North Queensland in 2002.

DESIGN

Epidemiological and entomological investigations; molecular analyses of the infecting parasites.

MAIN OUTCOME MEASURES

Case characteristics, adult and larval mosquito counts at the outbreak location, haplotyping of parasites in blood samples from different cases determined through sequencing of AMA1 and MSP1 genes.

RESULTS

A man with imported P. vivax malaria stayed at a camping ground 95 km north of Cairns in late September 2002. This led to an outbreak of P. vivax malaria in 10 adults who stayed at the camping ground in October. Large numbers of Anopheles farauti sensu lato larvae were present in stagnant pools in a creek at the camping ground, and many adult mosquitoes were collected nearby. Not only had most of the infected patients been exposed to mosquitoes at night, they were also less likely than other campers to have used insect repellents appropriately (odds ratio, 0.01; P < 0.001). Two different haplotypes of P. vivax, only one of which was detected in the imported case, were involved in the outbreak.

CONCLUSIONS

Although local transmission of malaria is rare in Far North Queensland, the risk is probably higher in the dry season (September to December). Campers need to be aware of the increased risk of mosquito-borne diseases. Sexual recombination of multiple gametocytes in mosquitoes infected by the imported case may have resulted in the two haplotypes of P. vivax involved in the outbreak.

Global change and human vulnerability to vector-borne diseases

Global change includes climate change and climate variability, land use, water storage and irrigation, human population growth and urbanization, trade and travel, and chemical pollution. Impacts on vector-borne diseases, including malaria, dengue fever, infections by other arboviruses, schistosomiasis, trypanosomiasis, onchocerciasis, and leishmaniasis are reviewed. While climate change is global in nature and poses unknown future risks to humans and natural ecosystems, other local changes are occurring more rapidly on a global scale and are having significant effects on vector-borne diseases. History is invaluable as a pointer to future risks, but direct extrapolation is no longer possible because the climate is changing. Researchers are therefore embracing computer simulation models and global change scenarios to explore the risks. Credible ranking of the extent to which different vector-borne diseases will be affected awaits a rigorous analysis. Adaptation to the changes is threatened by the ongoing loss of drugs and pesticides due to the selection of resistant strains of pathogens and vectors. The vulnerability of communities to the changes in impacts depends on their adaptive capacity, which requires both appropriate technology and responsive public health systems. The availability of resources in turn depends on social stability, economic wealth, and priority allocation of resources to public health.

Implications of climate change for parasitism of animals in the aquatic environment

Climate change can occur over evolutionary and ecological time scales as a result of natural and anthropogenic causes. Considerable attention has been focused in recent years on the biological consequences of global warming. However, aside from studies on those deleterious parasites that cause disease in man, little effort has been dedicated to understanding the potential changes in the parasite fauna of animal populations, especially those in aquatic systems. Predictions using General Circulation Models, among others, are examined in terms of their consequences for parasite populations in freshwater and marine ecosystems, concentrating on the temperate and boreal regions of eastern North America. Biological effects due to global warming are not predictable simply in terms of temperature response. It is also essential to explore the effects on aquatic parasites of alterations in host distribution, water levels, eutrophication, stratification, ice cover, acidification, oceanic currents, ultraviolet-light penetration, weather extremes, and human interference. Evaluation of the potential response of parasites of aquatic organisms to climate change illustrates the complexity of host–parasite systems and the difficulty of making accurate predictions for biological systems. Parasites in aquatic systems will respond directly to changes in temperature but also indirectly to changes in other abiotic parameters that are mediated indirectly through changes in the distribution and abundance of their hosts. Local extirpations and introductions may be expected as a result. In the long term, climatic change may influence selection of different life-history traits, affecting parasite transmission and, potentially, virulence.