The extinction of dengue through natural vulnerability of its vectorsArchived
Aedes aegypti is a highly specialized mosquito species feeding predominantly on humans and breeding in artificial water holding containers in urban areas, and currently restricted to subtropical and tropical areas. Williams et al. focus on the reasons why Ae. aegypti once occurred in locations where the mosquito does not occur anymore in Australia, the more temperate drier parts of the country.
Williams CR (1), Bader CA (1), Kearney MR (2), Ritchie SA (3), Russell RC (4).PLoS Neglected Tropical Diseases 2010 Dec 21; 4(12):e922.
Background: Dengue is the world's most important mosquito-borne viral illness. Successful future management of this disease requires an understanding of the population dynamics of the vector, especially in the context of changing climates. Our capacity to predict future dynamics is reflected in our ability to explain the significant historical changes in the distribution and abundance of the disease and its vector.
Methodology/principal findings:Here we combine daily weather records with simulation modelling techniques to explain vector (Aedes aegypti (L.)) persistence within its current and historic ranges in Australia. We show that, in regions where dengue presently occurs in Australia (the Wet Tropics region of Far North Queensland), conditions are persistently suitable for year-round adult Ae. aegypti activity and oviposition. In the historic range, however, the vector is vulnerable to periodic extinction due to the combined influence of adult activity constraints and stochastic loss of suitable oviposition sites.
Conclusions/significance: These results, together with changes in water-storage behaviour by humans, can explain the observed historical range contraction of the disease vector. For these reasons, future eradication of dengue in wet tropical regions will be extremely difficult through classical mosquito control methods alone. However, control of Ae. aegypti in sub-tropical and temperate regions will be greatly facilitated by government policy regulating domestic water-storage. Exploitation of the natural vulnerabilities of dengue vectors (e.g., habitat specificity, climatic limitations) should be integrated with the emerging novel transgenic and symbiotic bacterial control techniques to develop future control and elimination strategies.
VBORNET comment: 2011-03-16
Aedes aegypti is a highly specialized mosquito species feeding predominantly on humans and breeding in artificial water holding containers in urban areas, and currently restricted to subtropical and tropical areas. Williams et al. focus on the reasons why Ae. aegypti once occurred in locations where the mosquito does not occur anymore in Australia, the more temperate drier parts of the country. By means of mechanistic models (using CIMSiM), they challenge the idea that the historic range is climatically suitable for long term Ae. aegypti survival. They show that in some locations, the mosquito, for example, could only survive when permanent water holding containers were present. When prevalence of water tanks decreased, Ae. aegypti persistence reduced remarkably. Of course the reverse is also possible.
In Europe, until the beginning of the 20th century, the yellow fever mosquito was present in many areas and sea-ports along the Mediterranean coast, but disappeared rapidly during the 1950’s. To our knowledge no report provides convincing evidence why this had happened. The current study might provide clues that the species became extinct through its natural vulnerability in this region. Recently Ae. aegypti has established itself again on the island of Madeira (Portugal) through reintroductions by trade activities as well as on the north-eastern Black Sea coast. Expansions of the distribution of this mosquito due to global warming are expected, but other unidentified non-climatic factors might preclude this from happening. Generally, Ae. aegypti is not anticipated to reach as far north as Western Europe as it cannot withstand freezing temperatures. This study, however, makes you wonder whether man made changes or habits allow this mosquito to establish in apparently climatic unsuitable locations, as once seen in Australia. The authors conclude that Ae. aegypti is naturally vulnerable for extinction in certain conditions and that this vulnerability should be exploited in control programmes especially in subtropical and temperate regions. Yet, considering the increasing importance of Ae.albopictus as vector of dengue in these regions, it adds a level of complexity to such control programmes.
References:
- Sansom Institute for Health Research, University of South Australia, Adelaide, South Australia, Australia
- Department of Zoology, The University of Melbourne, Melbourne, Victoria, Australia
- School of Public Health, Tropical Medicine and Rehabilitation Sciences, James Cook University, Cairns, Queensland, Australia
- Department of Medical Entomology, Sydney Medical School, University of Sydney and Westmead Hospital, Sydney, New South Wales, Australia