Original article by Steve Lindsay and Rob Hutchinson at the School of Biological & Biomedical Sciences, University of Durham. Read about research into the likelihood of malaria returning to the UK.

 

Introduction

Could malaria ever return to the UK as a health impact of climate change? This question has sparked research being undertaken on marshes in the South of England. The following update on work in progress has also been submitted for publication to the Natural Environment Research Council, which is funding the project. The history of malaria alone makes fascinating reading.

 

An allegory of malaria in the marshes. Reproduced with the permission of the Wellcome Library, London.

Sections in this article

A History of Malaria in Britain

Predicted hotspots for malaria in the UK

Mosquito Research on the Isle of Sheppey

Collecting mosquitoes

Conclusion: Risk of Malaria in UK is low

Where Next?

A History of Malaria in Britain

Britain has a long history of malaria in the salt marshes along the coast of southern England and the disease was considered a leading cause of death in many marshland communities 200 years ago. Those areas most badly affected included the Fens, Thames Estuary, Essex marshes, Kent coast and Somerset levels. Malaria in England declined progressively from the 1840s onwards, but there were still pockets of the disease in parts of Kent and other low-lying parts of the country in the early 1900s. The last major outbreak occurred in Queenborough on the Isle of Sheppey during the First World War. Servicemen returning from Macedonia carrying malaria parasites in their blood were billeted on the edge of town. Here the infection was picked-up by local mosquitoes biting the convalescing soldiers. These mosquitoes then went on to infect 32 local people over a period of several years. From 1917 to 1952 there were 566 cases of indigenous malaria of which 90% were in or near coastal areas of southeast England. Most of these occurred between 1917 and 1921, after which outbreaks were sporadic with rarely more than 2 cases reported from an individual county each year. Only 34 such cases were reported between 1941-1948. With only one exception all of these reported cases were of a type described as vivax malaria. The last known cases of indigenous vivax malaria occurred in London in 1953 when two people were discovered suffering from malaria.  The carrier in this case was most likely a mosquito called Anopheles plumbeus that was found breeding in a tree hole near to the house of one of the patients.

Predicted hotspots for malaria in the UK

Areas sufficiently warm to support vivax malaria. Green areas show where transmission could occur for one month each year, yellow areas for two months and red dots are areas with Ague (=malaria) in the 19th Century. Lindsay & Thomas.

So much for the past, but what of the future? Is malaria likely to make a come back, particularly as global warming begins to heat up our marshes? Mathematical simulations of malaria risk in the UK highlight those areas of the country that could support this disease and show that they are close to sites that had malaria in the past. As our climate warms these areas of climate suitability are likely to expand and spread northward.

Mosquito Research on the Isle of Sheppey

It is one thing to have a climate warm enough for malaria, but this disease requires a suite of conditions to be met before transmission can occur. My colleague Rob Hutchinson and I are carrying out a study on the Isle of Sheppey to see whether local transmission is possible.

The salt marshes are a productive site for mosquitoes, although by far the commonest mosquito, Aedes detritus, cannot transmit malaria.  A recent survey carried out by Rob shows clearly that many people on the island find mosquitoes a real nuisance during the summer months and some individuals even sleep under a mosquito net to prevent themselves being bitten. The most likely carrier of malaria in the area, the mosquito, Anopheles atroparvus, is found less frequently in the marshes, but can occur in localised areas in high numbers as adults. This species is considered to be an efficient carrier of malaria since it feeds readily on people and often flies indoors where it can remain over winter. However, it is only capable of transmitting vivax malaria, a type of disease that is rarely life threatening.  Future work will show where its breeding sites are situated on the Island and how close they are to residential areas.

Collecting mosquitoes

A Second World War pillbox on the Island creates an ideal site for over-wintering female mosquitoes.

Collections of mosquitoes in the marshes are underway, although our progress has been severely hampered by the foot-and-mouth outbreak that prevented work on the island in summer 2001.  We're collecting adult populations throughout the winter months from derelict buildings, barns and cattle sheds.

Adult female mosquitoes resting on concrete.

The air temperature and relative humidity is being recorded at selected sites in order to relate the internal environment with choice of over-wintering site.  At present we have no explanation of why certain sites are chosen in preference to others.  We collect all visible adult mosquitoes in ten minutes at each site using a pooter (a special device which sucks up resting mosquitoes alive) and torch.  Only females over-winter, and they will take bloodmeals throughout the cold winter months.  We'll analyze the bloodmeals of these over-wintering females to assess the number of meals taken from humans.  An important factor in malaria transmission is the number of bites a person can expect to receive on a given night.  Initial human landing catches carried out this year on the island have shown that An. atroparvus will readily feed on humans.  These studies are going to expand during summer 2002 to identify what time of day this species prefers to bite and how being inside or outside a building affects the number of bites received.

Conclusion: Risk of Malaria in UK is low

During summer 2002 we'll be studying larval sites. We want to measure a number of parameters that may or may not be important in identifying a site.  By including several types of water measurements we should get a more accurate idea of the optimum conditions for An. atroparvus to breed. At the moment we only know that they prefer brackish water and the presence of algae.  All the information collected will allow the risk of malaria transmission to be assessed and determine what the important factors in local transmission are. 

It is extremely unlikely that vivax malaria will re-establish itself in the marshes of southern England since few people harbour the right sort of malaria parasites in their blood, and even those who do are likely to fall sick quickly and be treated with antimalarials, killing any parasites in the blood. The chances of being bitten by an infective mosquito are rather remote. We hope to confirm that there is little or no risk of these mosquitoes spreading malaria to the local population. Our work will shed light on the history of malaria in England and, we hope, reassure local people that English malaria is a disease of a bygone age.

Where Next?

On ClimateX.org

A good place to start for further reading is the article ‘Climate change and human health in Europe', which covers the broader health impacts that might be expected.

External links

The School of Biological Sciences, University of Durham is the host institution for Steve Lindsay and Andrew Hutchinson's work.