Climate change is going to mean mosquito-borne diseases spread north out of the tropics right? That seems to be the story the news media are giving us. But it is really the case? Do we really need to start thinking about buying bednets to protect against mozzy bites?
As editor of Global Health database I was invited to the ISNTD Bites seminar in London, at the Natural History Museum where the issue was hotly debated. The session on climate change and disease vectors showed that while biology of disease vectors like mosquitoes and sandflies is affected by temperature there are several other factors that influence spread of disease vectors and the diseases they carry that may mean they don’t spread in the way straight climate maps predict. Among these are land use, urbanisation and global trade. In fact, the entomologists at the seminar were arguing that climate change issues are distracting researchers from looking more into factors that are having drastic effects on the spread of disease vectors and disease right now.
So whats the verdict? Europe is still at risk of more vectorborne disease but it probably won't be climate change that is responsible. I don't think I'll get a bednet - yet.
I’ve included points from the relevant talks below with a take home message and if you want to read more see Further reading for papers cited by the speakers and sourced from Global Health database which covers vectorborne diseases and the vectors that carry them.
The Climatologist Dr Cyril Caminade (University of Liverpool):
The climate will become more suitable for Aedes albopictus mosquitoes in Europe
Dr Caminade’s predictions suggest Cyprus, Bulgaria, Slovakia, Turkey, Hungary, Benelux countries, Germany and Macedonia are all at risk of becoming homes for the mosquito that carries dengue fever. Its not all bad though, Spain and the Mediterranean coast would become less suitable in these models. The model includes temperature and rainfall predictions and assumptions about the overwintering ability of the mosquito and information about the mosquito’s current extent in Europe.
Dr Caminade admits the spread of disease vectors is a complex issue- although the climate might become more suitable, it is down to social and other factors as to whether the vectors and disease become established.
The view from the lab...Dr Courtney Murdock (Pennsylvania State University):
Temperature influences mosquito immunity and therefore its ability to carry disease but its not a simple picture.
Dr Murdock reminded us that mosquitoes live in a world of changing temperatures. Both changes in temperature through the day and night and the average temperature over a longer cycle could influence the ability of the mosquito to transmit disease. Dr Murdock’s studies show that important immune parameters are affected in different ways by temperature with some working best at 18 degrees and others at 30 degrees centigrade.. She warns that the consequence of this is that lab studies done at one temperature probably do not reflect what is happening in the field.
Ecological modelling... Dr Paul Ready (LSHTM)
Other factors are at work – vegetation types, altitude and sandfly overwintering factors are important for Leishmaniasis spread.
Dr Ready’s ecological studies identified landuse, altitude, density of the host(s) and the disease vector’s overwintering characteristics as key variables affecting spread of actual disease. His ecological modelling based on these factors showed that leishmaniasis carried by one species of sandfly could move up the French Atlantic coast while the other was unlikely to spread much further north.
Vector control specialist Dr Julian Entwistle (Xenex Associates)
The big question: is climate change important for transmission? Answer- no. we could be more at risk from the car tyres and the lucky bamboo trade…
Dr Entwistle argued that the theory that climate change will lead to wetter warmer weather and an increase in mosquito and other insect borne disease is shaky. There are lots of other important factors that have been shown to influence these diseases now: Urbanisation, travel, global trade. Aedes albopictus the disease vector responsible for dengue and chikungunya spread has been massively influenced by trade in used tyres and lucky bamboo rather than temperature changes.
Papers cited by the speakers plus more sourced from Global Health database.
Suitability of European climate for the Asian tiger mosquito Aedes albopictus: recent trends and future scenarios, Cyril Caminade, Jolyon M. Medlock, Els Ducheyne, K. Marie McIntyre, Steve Leach, Matthew Baylis and Andrew P. Morse. Interface 2012. doi: 10.1098/rsif.2012.0138
Potential impacts of climate change on the ecology of dengue and its mosquito vector the Asian tiger mosquito (Aedes albopictus). Erickson, R. A.; Hayhoe, K.; Presley, S. M.; Allen, L. J. S.; Long, K. R.; Cox, S. B.;, Environmental Research Letters, 2012, 7, 3, 034003,
LeishmaniaIntegrated Mapping of Establishment Risk for Emerging Vector-Borne Infections: A Case Study of Canine Leishmaniasis in Southwest France. Hartemink, N.; Vanwambeke, S. O.; Heesterbeek, H.; Rogers, D.; Morley, D.; Pesson, B.; Davies, C.; Mahamdallie, S.; Ready, P, PLoS ONE, 2011, August, e20817,
Environmental risk mapping of canine leishmaniasis in France. Chamaille, L.; Tran, A.; Meunier, A.; Bourdoiseau, G.; Ready, P.; Dedet, J. P. Parasites and Vectors, 2010, 3, 31, (8 April 2010)
Website:The EDEN project
Heterogeneity of environments associated with transmission of visceral leishmaniasis in South-Eastern France and implication for control strategies. Faucher, B.; Gaudart, J.; Faraut, F.; Pomares, C.; Mary, C.; Marty, P.; Piarroux, R.; PLoS Neglected Tropical Diseases, 2012, 6, 8, e1765
Complex effects of temperature on mosquito immune function. Murdock, C. C.; Paaijmans, K. P.; Bell, A. S.; King, J. G.; Hillyer, J. F.; Read, A. F.; Thomas, M. B., Proceedings of the Royal Society of London. Series B, Biological Sciences, 2012, 279, 1741, pp 3357-3366
Temperature-mediated differential expression of immune and stress-related genes in Aedes aegypti larvae. Muturi, E. J.; Nyakeriga, A.; Blackshear, M., Journal of the American Mosquito Control Association, 2012, 28, 2, pp 79-83
Vectorborne diseases spreading in Europe
The ecology of climate change and infectious diseases. Lafferty, Kevin D. Ecology . 2009, 90,:888–900.
Article: "Mosquitoes in Europe: an Emerging Threat", International Pest Control, 2012,Vol. 54, Number 4, See: http://www.isntdbites.com/#/entwistle/4568751259
Photo credit: Aedes- James Gathanay/CDC; Sandfly-CDC