Monday March 23 2015
Climate change could create an environment favourable to mosquitoes
"Mosquitoes heading for warmer UK," Sky News reports after a new review predicted climate change will make the UK a more hospitable environment for disease-carrying mosquitoes and ticks, leading to an outbreak of conditions normally seen in more tropical climates.
In the review, two authors searched the literature to identify evidence looking at the effect climate change in Europe could have on diseases carried by mosquitoes or other insects, such as ticks.
Mosquitoes thrive in warm and wet environments, so a rise in the average temperature could make the UK a more attractive destination. This could then lead to an increase in three diseases – malaria, dengue fever and chikungunya (a viral infection with symptoms similar to malaria) – in the UK by as early as 2030.
A review of this kind can only provide an estimate and cannot predict the future with 100% accuracy. However, it does show the potential public health dangers that could arise from climate change: a rise in the average temperature by just a few degrees centigrade could have a range of unpredictable effects on our environment.
Where did the story come from?
This study was written by two researchers from the Emergency Response Department, Public Health England (PHE), Porton Down. PHE is the NHS body responsible for protecting and improving public health in England.
One of the researchers received partial finding from the National Institute for Health Research's Health Protection Research Unit.
The study was published in the peer-reviewed medical journal Lancet Infectious Diseases.
What kind of research was this?
This was a literature review, where the researchers identified and discussed research on the effect climate change could have on the risk of vector-borne disease in the UK. Vector-borne disease is disease carried by a non-human organism (such as mosquitoes or ticks) that is then transmitted to humans.
The researchers searched literature databases to identify any published papers that had looked at vector-borne disease in Europe, and focused on reports that were potentially relevant to the UK.
They present a discussion of the issue and the evidence they identified. They also make various recommendations on monitoring and studying these vector-borne diseases, including how they are impacted by weather and climate.
The researchers clearly state that the views expressed in the article are theirs and "not necessarily those of the National Health Service, the NIHR, the Department of Health, or PHE".
What do the researchers say about mosquito-borne disease and climate change?
Insects regulate their body temperature by taking in heat from the environment. This means that increases in temperature could help them survive and incubate, thereby spreading any disease-causing organisms they carry, such as parasites, bacteria and viruses.
The researchers present evidence that has looked at the effects that 2C, 4C or 6C rises in average temperature could have on vectors carrying the following pathogens:
Of these pathogens, some (but not all) of the most extreme modelling scenarios suggest malaria could be present in the UK as early as 2030.
Climate assessment has suggested one type of mosquito that spreads dengue fever and chikungunya could theoretically live in warmer parts of the UK, and that by 2030 the climate could be even more well suited to this mosquito.
What do they say about malaria?
The researchers explain how malaria was regularly found in certain parts of the UK in the 1800s. The UK still has several species of mosquito capable of carrying the malaria parasite, albeit the less severe kind (Plasmodium vivax).
However, the researchers say rising summer temperatures could also support the development of the more severe malaria parasite (Plasmodium falciparum).
One group of researchers have modelled the effect climate change could have on P. falciparum. They estimate there will be between 1.5C and 5C increases in temperature between 2030 and 2100. Sustained transmission of the malaria parasite is still unlikely at these temperatures.
However, one of the most extreme model scenarios they looked at suggested there could be sustained transmission of the parasite (lasting at least one month of the year) in southern England by 2080 or, to a lesser extent, even as early as 2030.
But, as the researchers say, antimalarial drugs and the UK health system should be able to minimise transmission.
What do they say about dengue fever and chikungunya?
The researchers say that since 1990, five different tropical species of mosquito have become adapted to the temperate climate of Europe. These species are potential vectors of the tropical diseases dengue, chikungunya and yellow fever.
In the past decade, there have been cases where one of these tropical mosquito species has been implicated in outbreaks of chikungunya and dengue in southern France, Italy and Croatia.
Climate change is predicted to permit the expansion of this species across Europe, including the south of the UK.
If these mosquitoes do become established in the UK, people with dengue or chikungunya who travel to the UK would then be a source of infection for the established mosquitoes.
Ongoing transmission would then depend on the local climate conditions controlling mosquito populations.
Two models suggested that by 2030-50, the climate in southern England could be more suitable for one species of mosquito that carries chikungunya and dengue.
Models also predicted transmission periods of one month to be possible in London by 2041, and one to three months of activity possible in southern England by 2071-2100.
What do the researchers conclude?
The researchers make the following recommendations about how the potential threat from vector-borne disease could be managed:
- Continue to enhance UK surveillance of endemic and non-native vectors.
- Improve understanding of the effect of climate change and develop strategies to deal with changing public health risks in a changing environment (such as wetland management).
- Better understand the effect of extreme weather events (such as flooding and drought) on the risk of infectious disease, and work with environmental organisations to develop management plans to prepare for a disease outbreak resulting from an extreme event.
- Develop improved models that incorporate the many drivers for change (such as climate and land use) for a range of vector-borne diseases.
- Continue to work collaboratively across Europe sharing data on vector-borne diseases and risk assessment.
Overall, this review provides insights into how climate change might lead to the transmission of tropical diseases in what are currently temperate parts of the world, such as the UK. Predicting what may happen in the future can help countries make sure they are prepared for such an eventuality.
This review was informed by a search for relevant literature, but may not have captured or included all relevant studies. Most of the studies were modelling studies, which are reliant on various assumptions that may or may not turn out to be correct.
It's not possible to say with any certainty what will occur in the future. The authors also note that climate change is not the only factor affecting vector-borne diseases.
Many other factors are equally important, such as socioeconomic development and changes in how land is used. This adds to the difficulty in predicting exactly how much climate change might impact these diseases.
Analysis by Bazian. Edited by NHS Choices. Follow Behind the Headlines on Twitter. Join the Healthy Evidence forum.