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Volume 215 - Issue 4

The expanding geographic range of dengue in Australia

Author:  Annelies Wilder‐Smith

Med J Aust 2021; 215 (4): 171-172. || doi: 10.5694/mja2.51185
Published online: 16 August 2021

If suitable mosquito vectors are present in a region, returning infected travellers can initiate local transmission

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If suitable mosquito vectors are present in a region, returning infected travellers can initiate local transmission

Dengue outbreaks outside their usual geographic distribution — the subtropics and tropics of Asia, Africa, and Latin America — always attract media attention. The first major autochthonous dengue outbreaks in Europe were in Madeira (Portugal) in 2012;1 smaller clusters have been reported in France, Croatia,2 and Italy.3 Despite suitable mosquito vectors, the seasonal window for the establishment of dengue in Europe is short and the risk of its propagation, even in southern Europe, is low.4 It could, however, increase with global warming;5 for example, importation of dengue into more temperate climate zones in China has resulted in local outbreaks in cities such as Shanghai.6

Australia, particularly Far North Queensland, has also experienced several dengue outbreaks since 1995. These outbreaks were the result of importation of dengue by travellers, and fortunately limited in size.7 In response, Queensland Health has developed a comprehensive dengue control program that prevented the virus from becoming established in north Queensland. However, the rise in regional tourism, especially to popular destinations such as Bali,8 has increased the risk of its importation, and the urban centres of North Queensland (Cairns and Townsville) have established populations of the dengue vector Aedes aegypti.

In this issue of the MJA, Walker and colleagues report an autochthonous dengue outbreak during May–October 2019 in Rockhampton, central Queensland.9 Twenty‐one cases of locally acquired dengue virus serotype 2 (DENV‐2) infection were identified; genomic sequencing suggested that the outbreak was most closely related to Southeast Asian DENV‐2 strains. The authors conclude that the geographic range of dengue‐receptive areas in Australia has expanded from Far North Queensland into central Queensland, and suggest that maps for dengue‐receptive areas should be redrawn.9 Community engagement and vector control in Queensland should be expanded to include Rockhampton and the surrounding areas.

However, it should be noted that the geographic range of local dengue virus transmission was once substantially wider than as now defined.10 Indeed, the re‐classification of low risk areas as moderate or high risk should be routinely reviewed according to the geographic spread or introduction of mosquito vectors into different parts of Australia. The Queensland Health Dengue management plan 2015‒202011 already designates areas of central Queensland in which suitable vectors, such as Ae. aegypti, are present as being at moderate risk. Further, southeast Queensland, particularly Brisbane, has also experienced dengue outbreaks in the past, and protracted drought conditions and mandatory water restrictions during the early 2000s resulted in increased use of water harvesting and water containers, factors associated with increased container‐breeding mosquito risk.12

Health authorities in all Australian jurisdictions should heed the experience of central Queensland in 20199 and plan accordingly for strategic responses to the local establishment of Ae. aegypti or Ae. albopictus populations. Ae. albopictus is not currently established on mainland Australia but its introduction would not only elevate the risk of dengue but also markedly expand the region at risk, given the temperate climate tolerance of this species. Predictive models coupled with climate tolerance experiments suggest that a Torres Strait strain of Ae. albopictus could be easily imported into Australia, overwintering in the egg stage and then proliferating during summer.13

The key message of the report by Walker and her colleagues9 is that, if vectors for dengue transmission are present in a region, there is a risk of local transmission given pathways of introduction by infected travellers. Health authorities must respond accordingly.

The Rapid Surveillance for Vector Presence system — a powerful tool for the surveillance of invasive Aedes mosquitoes, validation of species eradication, and quality assurance for vector control operations during disease outbreaks — has been introduced in Australia.14 Further, Australian researchers have developed promising novel control strategies based on the fact that Ae. aegypti mosquitoes infected with the wMel strain of Wolbachia pipientis are less susceptible to dengue virus infections than wild‐type Ae. aegypti. In a recent large scale trial in Indonesia, this approach reduced the number of dengue cases by more than 80%.15 Field studies have also been conducted in Far North Queensland, where, despite increasing dengue importation by travellers, releasing the wMel strain of Wolbachia effectively prevented further dengue outbreaks.16 Similar novel control strategies may need to be extended to other areas of Australia with receptive mosquito populations.

 

Author

  • Annelies Wilder‐Smith1,2
  • 1. Institute of Social and Preventive Medicine, University of Bern, Bern, Switzerland
  • 2. Heidelberg Institute of Global Health, University of Heidelberg, Heidelberg, Germany

Correspondence: annelies.wilder-smith@uni-heidelberg.de

Competing interests

No relevant disclosures.

References

Linked content

  • MJA Research Letter: Re‐defining the dengue‐receptive area of Queensland after the 2019 dengue outbreak in Rockhampton

Provenance: Commissioned; externally peer reviewed.

View this article on Wiley Online Library