EDEN project puts emerging vector-borne diseases under the microscope
In the years following World War Two, there was a wave of optimism in Europe that vector-borne diseases such as malaria and tick-borne encephalitis, could be eradicated using newly discovered treatments and vaccines. But the recent re-emergence of several vector-borne, parasitic and zoonotic diseases, has suggested that this optimism may now be premature. A variety of reasons for these outbreaks have been suggested, such as human-induced changes to the landscape, changes in human behaviour and climate change. But understanding of the underlying biological processes is not thorough enough for scientists to propose predictive models of disease occurrence or risk maps for international and national public health agencies. Now EDEN, an EU-funded project, is hoping to shed some light on the matter. It aims to catalogue, understand, model and map the environmental, economic and societal factors leading to the rise of these diseases. 'We want to give public health services and policy-makers early-warning and decision tools with which they can inform the general public of the current health risks and evaluate progress in controlling these emerging and existing diseases,' Dr Renaud Lancelot, project coordinator, told CORDIS News. But identifying these factors is no easy feat. For instance, the outbreak of tick-borne encephalitis, or TBE, in the Czech Republic pays testament to the complex factors involved. In 2006, the authorities registered some 1,000 cases of this potentially deadly disease, which is transmitted by deer ticks. This represented 60% more cases than in 2005. 'The Czech Republic is a small country; imagine the impact at a European scale,' said Dr Lancelot. One possible reason given for the outbreak was that the country experienced a relatively wetter April and May, leading an increase in the tick population. Another theory put forward was that a warm autumn with an exceptionally high yield of mushrooms resulted in more people taking to the woodlands, which could have led to more people being exposed. 'But it's not just climate change that is causing the spread of this disease,' says Dr Lancelot. Socio-political factors also need to be taken into account. Experts charting the spread of TBE noticed that a dramatic rise in cases occurred in the North and East of Europe shortly following the fall of communism. At this time both poverty and wealth increased. People moved away from collective farming in favour of small-scale private farming, taking themselves and their livestock into tick-infested forests and fields. 'This led to a change in the landscape which was favourable to this disease,' noted Dr Lancelot. 'Some people couldn't adapt to the economic changes and found themselves in a state of poverty; they turned to the land to exploit its natural resources, going more frequently into the forest to pick berries and mushrooms. This meant that they came into contact with the ticks,' explained Dr Lancelot. 'For others, their economic situation improved. With more free time on their hands, these people went walking in the forests, leading to a higher risk of infection.' These different factors, together with the termination of mass vaccination campaigns against TBE (which were subsidised by the governments during the communist period), led to a dramatic increase of clinical cases from the early 1990s. Another disease, the emergence of which is puzzling experts, is 'Hemorrhagic Fever With Renal Syndrome' (HFRS), which is spread by voles and other small rodents that live in forests. People catch the disease when they come into contact with the urine of these rodents. In 2005, more than 1,000 cases were confirmed in a region located in north-eastern France, Belgium, the Netherlands, Luxemburg and Germany. The disease is also very frequent in Scandinavia 'While rodent population dynamics obviously plays a major role in HFRS, we don't fully understand why this disease is re-emerging,' said Dr Lancelot. He surmises that social factors may have a role to play in the disease's outbreak. Malaria, which was thought to have been eradicated in Europe, may also be making a comeback. In 2006, two cases of infection were identified in Corsica. 'Neither victim had been travelling nor did they live close to an airport,' noted Dr Lancelot, who point out that the mosquitoes that infected them were indigenous to Corsica. This is the first case of locally derived or 'autochthonous' malaria in Corsica in 35 years. 'Milder winters mean the mosquitoes which carry the disease, and others possibly carrying Dengue Fever or Chikungunya, can breed and survive far further north than in the past. 'It shows that the vectors haven't disappeared,' added Dr Lancelot. The EDEN project is oriented towards research. It aims at elucidating the mechanisms of these epidemiological changes and at elaborating models representing disease spread and transmission. In this respect, the first publications from the teams involved in the project are very encouraging (the 50th EDEN publication was released in June 2007, and the 100-mark may be reached in early 2008). With the continuing support of EU and cooperation of other funding schemes and agencies, new projects, more oriented towards innovation and development, will use these results to develop surveillance and early-warning systems for the benefit of European inhabitants, and more generally, for those people exposed to the risk of these emerging diseases. The project, which will run until 2010, received €11.5 million under the 'Sustainable development, global change and ecosystems' thematic priority of the Six Framework Programme (FP6).