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Looking down on disease
Cross-talk
Looking down on disease Despite the doomy headlines, global warming may bring health benefits as well as hazards. Across the board, a rise in the average global temperature is likely to result in more heat-related deaths but also fewer cold-related deaths. Predictable increases in the incidence of malaria, as mosquitoes find new breeding grounds, could be accompanied by a decline in schistosomiasis, since the snails that carry Schistosoma spp are exquisitely sensitive to temperature. But there may well be a wider good—a strengthening of our belief that alterations in the pattern of communicable disease can and should be fathomed more keenly in advance. Given the panoply of modern techniques, from satellite surveillance to molecular epidemiology, much more could surely be done to forecast potentially threatening shifts in microbial behaviour. These thoughts are triggered by the Asian tiger mosquito, Aedes albopictus, which this summer has found an ecological niche for the first time in southern Europe. Its arrival was signalled by an illness that affected just under 200 people in two villages in the Italian province of Ravenna. Although the symptoms of headaches, nausea, and fatigue were mild, the clustering of cases attracted medical attention, leading to the diagnosis of chikungunya. A albopictus is a vector for this and several other viral diseases. As reported in Science (2007; 317: 1485), India witnessed an explosive epidemic of chikungunya in 2006, with over a million cases. More than a third of the 800 000 population of Réunion, a French island in the Indian Ocean, also contracted the infection in 2005–06. Although sporadic imported cases have been identified previously in Europe, local transmission had never been known until the Ravenna outbreak. International disease surveillance systems have developed considerably in recent decades. However, there is one specific approach that is as yet under-used: monitoring from space. Of course, existing satellites carry sensors that detect changes in several parameters relevant to infections—for example, weather, land use, and crop cultivation. Yet, as pointed out recently by Gregory Glass of the Johns Hopkins Bloomberg School of Public Health (Baltimore, MD, USA), there have been just a few occasions when terrestrial medicos have used data of this sort to help in charting and indeed predicting alterations in patterns of disease. “The presence of Landsat imagery extending from the late 1980s and 1990s enabled us to relate environmental conditions to the occurrence of the first recognised outbreak of hantavirus pulmonary syndrome in the US southwest in 1993, but also led us to recognise that similar conditions had occurred in the late 1980s when conditions were suitable for a large outbreak in much the same region”, http://infection.thelancet.com Vol 7 December 2007
Glass writes in Future Medicine (2007; 2: 225–29). “The continuation of the Landsat program has allowed us to characterise the year-to-year variation in human risk for the region almost 10 months in advance of the transmission season during the past decade.” Another example has been the use of satellite imagery to identify environmental conditions leading to the emergence of flood-water mosquitoes carrying Rift Valley fever virus, before infection became manifest in either livestock or human beings. Measures of this sort can provide valuable time for the organisation of immunisation programmes. Glass points out that some uses of satellite observations are even more elementary, as in the enumeration of migrant populations and activities in transportation networks. This type of information, on footpaths in subSaharan Africa, can help public-health authorities to identify potential routes through which pathogens are likely to be disseminated. These insights may be unobtainable in any other way. In view of the success of several demonstration projects in the past, why are “plague forecasts” not available on the evening television news, or on the web, especially in those regions of the world most likely to benefit? Gregory Glass deserves considerable credit for asking this simple yet pertinent question. Those in control of relevant funding need to take account of his persuasive answer—that, while the interdisciplinary nature of this field makes the mounting of such a real-life decision-support system a huge challenge, it is not insurmountable.
For more information on the chikungunya outbreak in Italy see Lancet Infect Dis 2007; 7: 641
For more information on chikungunya in India and Réunion see Lancet Infect Dis 2007; 7: 319–27
Bernard Dixon 130 Cornwall Road, Ruislip Manor, Middlesex HA4 6AW, UK; [email protected]
765
Looking down on disease Despite the doomy headlines, global warming may bring health benefits as well as hazards. Across the board, a rise in the average global temperature is likely to result in more heat-related deaths but also fewer cold-related deaths. Predictable increases in the incidence of malaria, as mosquitoes find new breeding grounds, could be accompanied by a decline in schistosomiasis, since the snails that carry Schistosoma spp are exquisitely sensitive to temperature. But there may well be a wider good—a strengthening of our belief that alterations in the pattern of communicable disease can and should be fathomed more keenly in advance. Given the panoply of modern techniques, from satellite surveillance to molecular epidemiology, much more could surely be done to forecast potentially threatening shifts in microbial behaviour. These thoughts are triggered by the Asian tiger mosquito, Aedes albopictus, which this summer has found an ecological niche for the first time in southern Europe. Its arrival was signalled by an illness that affected just under 200 people in two villages in the Italian province of Ravenna. Although the symptoms of headaches, nausea, and fatigue were mild, the clustering of cases attracted medical attention, leading to the diagnosis of chikungunya. A albopictus is a vector for this and several other viral diseases. As reported in Science (2007; 317: 1485), India witnessed an explosive epidemic of chikungunya in 2006, with over a million cases. More than a third of the 800 000 population of Réunion, a French island in the Indian Ocean, also contracted the infection in 2005–06. Although sporadic imported cases have been identified previously in Europe, local transmission had never been known until the Ravenna outbreak. International disease surveillance systems have developed considerably in recent decades. However, there is one specific approach that is as yet under-used: monitoring from space. Of course, existing satellites carry sensors that detect changes in several parameters relevant to infections—for example, weather, land use, and crop cultivation. Yet, as pointed out recently by Gregory Glass of the Johns Hopkins Bloomberg School of Public Health (Baltimore, MD, USA), there have been just a few occasions when terrestrial medicos have used data of this sort to help in charting and indeed predicting alterations in patterns of disease. “The presence of Landsat imagery extending from the late 1980s and 1990s enabled us to relate environmental conditions to the occurrence of the first recognised outbreak of hantavirus pulmonary syndrome in the US southwest in 1993, but also led us to recognise that similar conditions had occurred in the late 1980s when conditions were suitable for a large outbreak in much the same region”, http://infection.thelancet.com Vol 7 December 2007
Glass writes in Future Medicine (2007; 2: 225–29). “The continuation of the Landsat program has allowed us to characterise the year-to-year variation in human risk for the region almost 10 months in advance of the transmission season during the past decade.” Another example has been the use of satellite imagery to identify environmental conditions leading to the emergence of flood-water mosquitoes carrying Rift Valley fever virus, before infection became manifest in either livestock or human beings. Measures of this sort can provide valuable time for the organisation of immunisation programmes. Glass points out that some uses of satellite observations are even more elementary, as in the enumeration of migrant populations and activities in transportation networks. This type of information, on footpaths in subSaharan Africa, can help public-health authorities to identify potential routes through which pathogens are likely to be disseminated. These insights may be unobtainable in any other way. In view of the success of several demonstration projects in the past, why are “plague forecasts” not available on the evening television news, or on the web, especially in those regions of the world most likely to benefit? Gregory Glass deserves considerable credit for asking this simple yet pertinent question. Those in control of relevant funding need to take account of his persuasive answer—that, while the interdisciplinary nature of this field makes the mounting of such a real-life decision-support system a huge challenge, it is not insurmountable.
For more information on the chikungunya outbreak in Italy see Lancet Infect Dis 2007; 7: 641
For more information on chikungunya in India and Réunion see Lancet Infect Dis 2007; 7: 319–27
Bernard Dixon 130 Cornwall Road, Ruislip Manor, Middlesex HA4 6AW, UK; [email protected]
765