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Montpellier will be hosting the annual meeting of the EDEN project from 10 to 12 May 2010 (press release – CIRAD, December 2009)

Research units

Emerging and Exotic Animal Disease Control

Contact

Renaud Lancelot
Montpellier, France
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Renaud Lancelot: "Climate change is just one of the factors in emerging diseases"

11/12/2009 - Article

It is commonly accepted that emerging diseases are linked to climate change. The results of the EDEN project (Emerging Diseases in a changing European ENvironment ) nuance that idea considerably. Interview, on the occasion of the Copenhagen climate change conference, with Renaud Lancelot, a CIRAD epidemiologist and EDEN project coordinator.

We have recently seen renewed growth in emerging diseases, often of animal origin. How can this renewal be assessed?

Renaud Lancelot: There has indeed been an increase in the frequency of emerging diseases, which has been observed over a long period. In the decade from 1940 to 1950, some twenty such events were recorded, whereas there were more than eighty during the decade from 1980 to 1990. Most of these diseases have animal reservoirs, and some affect animals and humans: they are known as zoonoses.

What are the causal factors behind this resurgence, and in particular, what is the role of climate change?

R.L.: When the EDEN project was launched five years ago, the prevailing idea was that these diseases were linked to environmental change, and particularly climate change. The reality is more complex. Climate change obviously plays a role, but not in the way or the sense that we rather naively imagined it. The work done under the EDEN project has allowed us to pinpoint the influence of climate change on some of these diseases, and to place it in perspective, on a small and large scale, with other types of change. These other types include the interaction between man and the ecosystems in which he lives: cultivating land or leaving it fallow, and deforestation and even increases in wooded areas, as is sometimes the case in Europe. Forests encourage the presence of small and large mammals (rodents, deer, etc), which are parasitized by ticks that carry animal and human diseases.

However, one of the main factors that account for disease transmission to man is poverty, or more generally precarious socio-economic conditions. Lassa fever, which affects West Africa, is a good example. The disease is caused by a virus carried by a rodent and excreted in its urine and faeces, hence contaminating the surrounding environment. It affects some two million people a year and causes 5 to 10 000 deaths. The geographical distribution of the virus is governed by climatic factors, such as different rainfall patterns and, to a lesser extent, temperature. However, the disease is not necessarily seen in man wherever the virus is found. Epidemics primarily strike regions hit by social unrest, such as refugee camps, where there is greater contact between people and environments soiled by rodents.

In radically different conditions, Finland is faced with another viral disease transmitted by rodents: haemorrhagic fever with renal syndrome (HFRS). In this case, climate change has resulted in milder winters than in the past, with less snow and more rain to flood rodent dens. The rodents have taken refuge in houses and manmade shelters, which has increased the risk of human infection. Finland saw a record epidemic peak during the winter of 2008-2009, with 3500 cases of HFRS for a total population of just over 5 000 000.

What are the regions that are most exposed to this increase in emerging diseases?

R.L.: Africa is very exposed, as are certain regions of Asia and South America. Within Africa, the Gulf of Guinea and the Lake Victoria Basin are high-risk zones. The Mediterranean, the Sahel and southern Africa are also more vulnerable as a result of climate change. We can expect some zones that have become unsuitable for agriculture to be abandoned, and human population density to increase in other less affected regions, hence increasing the risk of contact with emerging pathogens. Moreover, regions in which there is currently an epidemiological balance, due to regular exposure to pathogens, risk seeing that balance upset and epidemic episodes occurring. There are fears of a phenomenon of this type with malaria in the Sahelian strip in Africa.

However, it is important to stress that our knowledge of the biological and ecological aspects of epidemiological cycles is still limited in many cases. The EDEN project's approach is to use our knowledge of such processes to develop predictive models that can be used to focus surveillance operations and assess the chances of success of disease control methods. This means having access to reliable sanitary data. There is still a lot to be done in this field in Africa, including to improve disease diagnosis and collaboration with international reference laboratories. Human resources and technological platforms need to be boosted considerably. CIRAD and its partners in France and elsewhere in Europe have a major role to play in this dynamic, in synergy with regional surveillance networks and international organizations.

Interview by Elsa Bru