The incidence of a variety of infectious diseases has been linked to the weather and climate in a report published by the American Academy of Microbiology.
Patterns of disease seem to be closely connected to weather, not just the expected seasonal return of influenza but also changed incidence associated with intermittent events such as the recent El Nino.
The report highlights recent research which suggested that increases in the rates of malaria, cholera, Rift Valley fever and hantavirus pulmonary syndrome were associated with El Nino.
"In Colombia, increases of up to 20 per cent in the incidence of malaria have been recorded in the year following an El Nino," according to the Academy report.
A 1993 outbreak of the deadly hantavirus pulmonary syndrome in the south west of the United States was related to the increased rainfalls associated with El Nino.
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, a known carrier of the hantavirus, thereby setting the stage for an outbreak.
Satellite data had also been effective in demonstrating a link between El Nino in the early 1990s and cholera outbreaks in Peru and along the Bay of Bengal.
El Nino was not the only weather variable that could affect disease incidence, according to the report. Variables including air and water temperature, rainfall levels, and wind and ocean currents were also associated with outbreaks.
"It is striking how sensitive to weather and climate fluctuations so many of these diseases are," stated Dr Jonathan Patz of Johns Hopkins University, who is a co-author of the report.
"We can't just focus on the microbe any more. 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," he said.
"The seasonality of many human diseases has long been recognised, but it is only recently that this aspect has become a major study in infectious disease research," stated Dr Rita Colwell, who is chair of the Academy's board of governors and the other co-author of the report.
"Up until now, the principles of ecology have not been incorporated into epidemiology."
The report calls for more interdisciplinary research by scientists working in areas such as microbiology, infectious disease, epidemiology and climatology, and a sharing of databases to understand better the links between weather and disease.