Scientists are discovering more about the intricate relationship between global weather patterns and infectious disease, thanks in part to recent advances in molecular biology, meteorology and satellite imaging, resulting in a new interdisciplinary field of research, says a report by the American Academy of Microbiology.
"The seasonality of many human diseases has long be recognized, but it is only recently that this aspect has become a major study in infectious disease research," says Rita Colwell, Chair of the Academy's Board of Governors and a coauthor of the report. "Up until now, the principles of ecology have not been incorporated into epidemiology."
"We can't just focus on the microbe anymore," says Jonathan Patz of Johns Hopkins University, the other coauthor of the report. "We can't sort out the dynamics of many of these infectious diseases without meaningful interdisciplinary work. It is not just a simple relationship between weather variables and pathogens. We need to connect existing databases on such factors as land use patterns, deforestation, and soil moisture to public health outcomes."
The report is based on a colloquium convened by the Academy in June 1997. An international group of scientists from a variety of disciplines including microbiology, infectious disease, epidemiology, risk assessment and climatology gathered to discuss the effects of weather and climate factors on the incidence of infectious disease. Because of the range of expertise represented, this meeting "will be viewed as a seminal jumping-off point" for future research on the link between climate and infectious diseases, says Colwell.
The recent strong El Niño provides a good example for studying the effects of climate change on patterns of infectious disease. Recent research suggests that increases in the rates of malaria, cholera, Rift Valley fever and hantavirus pulmonary syndrome are associated with the effects. In Columbia, increases of up to 20% in the incidence of malaria have been recorded in the year following an El Niño . Satellite data has also been effective in demonstrating a link between El Niño in the early 1990s and cholera outbreaks in Peru and along the Bay of Bengal.
The 1993 outbreak of deadly hantavirus pulmonary syndrome in the Southwest United States has also been shown to be related to increased rainfalls that were associated with El Niño. Higher rainfalls increased the production of pinon nuts, which are an important food source for the deer mouse. An abundant food source caused an increase in the population of the deer mouse which is a known carrier of the hantavirus, thereby setting the stage for an outbreak.
El Niño is just one high profile example of the effect of climate and weather on infectious disease outbreaks, says the report. A number of variables including air and water temperature, rainfall levels, and wind and ocean currents are also associated with outbreaks. For example, the number of cases of the foodborne pathogen Cyclospora cayetanesis in children in Peru has been associated with air temperature in a yearly cycle.
"It is striking how sensitive to weather and climate fluctuations so many of these diseases are," says Patz.
One of the immediate results of the colloquium was the establishment of a research project called the El Niño-Southern Oscillation (ENSO) Experiment. Coordinated by the National Oceanic and Atmospheric Administration, the ENSO experiment is taking an in-depth look at the effects of the most recent El Niño. The results will be presented at the follow-up colloquium on these issues to be held in the Fall of 1999. The establishment of the ENSO Experiment addresses one of the recommendations of the report: that long term research projects, exceeding the normal 2-3 year funding cycle, be supported.
The report also recommends the networking of databases to provide researchers access to information from a variety of sources and the standardization of formats for collecting and reporting such data. The availability of this data in consistent formats is essential for enhancing research in climate and health, says the report. Other recommendations include education and training of new researchers, communication of new knowledge to the public and the encouragement of journals to publish results of research that falls outside or straddles traditional disciplinary boundaries. The report stopped short of recommending establishment of a new journal, but stressed the importance of ensuring that this research be published and disseminated within the scientific community.
The American Academy of Microbiology is an honorific leadership group within the American Society for Microbiology (ASM) whose mission is to foster and recognize scientific excellence in the microbiological sciences. Its activities include convening colloquia to develop consensus-building position papers that provide expert scientific opinion and advice on current and emerging policy issues in microbiology.
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The complete report can be accessed on the World Wide Web at http://www.asmusa.org/acasrc/aca1.htm.
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