Mapping the spread of the Aedes aegypti and Aedes albopictus mosquitoes

Over the last decades, factors including human movement and climate change have opened up opportunities for the dramatic expansion of disease-carrying mosquitoes into new regions. In recent research, an international and multidisciplinary team have used statistical mapping techniques to understand the spread of both species in Europe and the United States and draw attention to likely patterns of future expansion. In this Infectious Thoughts interview, we speak with Dr. Moritz Kraemer about the role of mapping in informing targeted policies for future mosquito control, and the need for involvement of sectors as diverse as infrastructure development, climate change and civil society to improve the data and surveillance of mosquitoes worldwide.

What were some of the main reasons for which you chose to focus your work on the expansion of the mosquitoes Aedes aegypti and Aedes albopictus?

Both species have been rapidly expanding over the last decades. Aedes aegypti for example is the most important vector transmitting dengue, yellow fever, chikungunya and zika virus and we hope that these maps will provide a baseline for making decision how to slow down their spread.

What are the main factors driving the expansion of the Aedes mosquitoes globally?

We find that over the past two decades the rapid expansion of both vectors can be well explained by human mobility. Going further into the future however we anticipate that increases in temperature and continued urbanization drive most of the expansion of these species

Fig 1: Predicted global geographical distribution of Ae. aegypti and Ae. albopictus

The distribution of Ae. aegypti (a) and Ae. albopictus (b) in 2050 under the medium climatic scenario RCP 6.0 and uncertainty for Ae. aegypti (c) and Ae. albopictus (d).

Where are some of the regions where you are recording the most rapid increases in Aedes? Have these results been expected?

Our maps pin-point locations that are most at risk of receiving new populations of these species. Interestingly these differ between both species as they have different biting preferences and biology. For example, Ae. aegypti is expected to spread to new urban areas in China and the USA. Aedes albopictus expansion is mostly concentrated around its existing distribution.

Fig 2: Predicted future spread of Ae. aegypti and Ae. albopictus in the United States

Spread was estimated using human-mobility metrics and ecological determinants fitted to past occurrence data. a, Forecasted change in the distribution of Ae. aegypti between 2020 and 2050 using the medium climatic scenario RCP 6.0 at the US county-level ranging from −0.25 (blue) to 0.25 (red). Red indicates expansion and dark blue contraction of the Aedesrange distribution between 2020 and 2050. b, The predicted habitat suitability for the presence of Ae. aegypti in 2050. Pixels with no predicted suitability are in grey. c,d, The corresponding results of a and b for Ae. albopictus.

Your work has outlined some of the main trends in the spread of Aedes mosquitoes - given these, what are some further implications of cryptic breeding sites? How could your work and conclusions spur specific industries such as construction and urban planning to raise mosquito-proofing in their priorities?

We believe that the work presented enables targeted surveillance and control of both species. More work however is needed to investigate the small scale patterns and drivers of mosquito abundance and one aspect we are currently investigating is quality of housing as well as sanitation and urban infrastructure. From historic data we see that the introduction of piped water and infrastructure in general have led to reductions in mosquito abundance.

How could citizen science input into mosquito surveillance systems and ultimately inform vector control programmes? How could the health community engage more with a range of partners such as the public, customs officials, global supply chains, migration agencies, ...

Mosquito spread is a very complex issue and requires different stakeholders to work together, including the public, health agencies etc. Our maps have already been used by vector surveillance teams to investigate the hotspots of mosquito spread, including ports and along highways.

Similarly, these maps can be used to make policies to continue efforts to reduce the spread of the species across multiple countries. Citizens can help support these efforts through monitoring open water containers around their houses and neighbourhoods.

Which technologies or partnerships would you like to see developed to help with your ongoing research and surveillance projects?

It will be very important to increase the accuracy and volume of the data available to date. We hope to inspire work on monitoring mosquito abundance along major importation corridors and continue to curate a database that can then be used to update our predictions. This could include citizens to take images of mosquitoes that can then be validated by experts and entered into a database.