Sir--In your news item on the Kyoto Summit (Dec 20/27, p 1825), Justin McCurry reports on warnings that man-made climate change may unleash a public-health disaster. Specifically he mentions "adamant" claims by Paul Epstein and Andrew Haines that global warming has already caused malaria, dengue, and yellow fever to invade higher latitudes in the temperate regions and higher altitudes in the tropics.
Such claims, oft repeated, plainly ignore the past. Until the 20th century, malaria was a common disease throughout much of the USA, and it remained endemic until the 1950s. Yellow fever played a major part in US history. Widespread epidemics of dengue were also common, and continued until the 1940s. In Europe, malaria was probably present in neolithic times. In ancient Greece, Hippocrates clearly distinguished between the symptoms of vivax and falciparum malaria. Throughout history, nearly all countries of that continent were affected. Even in the present century, devastating epidemics occurred as far north as Archangel on the Arctic Circle, and the disease remained endemic in such un-tropical countries as Holland, Poland, and Finland until after World War II.2 Yellow fever also killed tens of thousands in many European countries until the end of the 19th century, and a devastating epidemic of dengue, with an estimated 1 million cases and 1000 deaths, occurred in Greece in 1927-28.3
Claims that malaria and dengue have recently climbed to higher altitudes are equally uninformed. Highland malaria was widespread throughout the world until the era of DDT and cheap malaria prophylaxis. The figure shows the maximum altitude of autochthonous cases in 11 countries in the early half of this century. Transmission occurred to 2600 m in Kenya, and 2450 m in Ethopia. In the Himalayas, the disease was present to 2500 m in India and 1830 m in China. In the Andes, epidemics were recorded to 2180 m in Argentina and 2600 m in Bolivia. In the latter country, cases actually occurred to 2773 m, transmitted by mosquitoes breeding at 35°C in thermal springs.
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Multiple regression curve is approximate guide to relation between maximum altitude and latitude. ( |
) altitude of 1987 epidemic
of malaria in Madagascar; (m) altitude of 1993 epidemic of dengue in Costa Rica. Both are well below maximum altitudinal limits for their
latitude. Figure is drawn from Hackett's data. (Hackett LW. The malaria of the Andean region of South America. Revista del Instituto
de Salubridad y Enfermedades Tropicales 1945; VI: 239-52).
Recent epidemics of malaria in the highlands of Madagascar have been attributed to global warming, although they occurred well below the maximum altitude for transmission (figure) and were clearly a sequel to a breakdown of control infrastructure. Moreover, similar epidemics had taken place in the same areas in 1878 and 1895, and local records show no great change in temperature.4 Similarly, recent dengue transmission at 1250 m in Costa Rica followed the reappearance of the vector Aedes aegypti (Linn) after a successful period of control, and there is no evidence to support the suggestion that transmission was due to putative climate change. Lastly, repeated claims that the disease has ascended to new altitudes in Colombia consistently cite a publication by Nelson et al5 but ignore its content, for although the vector was present to 2200 m, the investigators clearly stated there were no cases at high altitude, and none have been reported since that study.
The distortion of science to make predictions of unlikely public-health disasters diverts attention from the true reasons for the recrudescence of vector-borne diseases. These include the large-scale resettlement of people (often associated with major ecological change), rampant urbanisation without adequate infrastructure, high mobility through air travel, resistance to antimalarial drugs, insecticide resistance, and the deterioration of vector-control operations and other public-health practices.
Paul Reiter
Dengue Branch, Division of Vector-Borne Infectious Diseases, National Center for Infectious Diseases, Centers for Disease Control and Prevention, Dengue Branch, San Juan, Puerto Rico 00921-3200, USA (e-mail: ipr1@cdc.gov)
1 M cCurry J. Physicians add their warnings to Kyoto summit. Lancet 1997; 350: 1825.
2 Bruce-Chwatt LJ, de Zulueta J. The rise and fall of malaria in Europe, a historico-epidemiological study. Oxford: Oxford University, 1980: 240.
3 Copanaris P. L'épidemie de dengue en Grèce au cours de l'été 1928. Office International d'Hygiene Publique 1928; Bulletin 20: 1590-601.
4 Mouchet J, Laventure S, Blanchy S, et al. La reconquête des Hautes Terres de Madagascar par le paludisme. Bull Soc Pathol Exot 1997; 90: 162-68.
5 Nelson MN, Suarez MF, et al. The distribution of Aedes aegypti at high elevations in Colombia. World Health Organization 1983; WHO/VBC/83.872.