WASHINGTON • Many scientists agree that climate change will likely influence the spread of infectious diseases, from the mosquito-borne like Zika to the bacteria found in contaminated food and water.
It is a relationship that has largely been studied in developing nations, where the cumulative effects of global warming are likely to be more severe. Research on cholera and malaria, for instance, suggests rising temperatures may boost transmission.
But new research suggests that higher-income nations should not write off the problem either.
The study, published on Monday in Proceedings of the National Academy of Sciences, finds short-term shifts in climate and weather patterns, brought on by El Nino, have a history of influencing disease outbreaks in the United States - giving an important glimpse into what the effects of climate change may bring in future.
"There's this idea that the vulnerabilities are really only in low-income countries," said Professor David Fisman, the lead author and professor of epidemiology and medicine at the University of Toronto's Dalla Lana School of Public Health.
The researchers found that El Nino conditions were associated with a higher risk of vector-borne diseases - diseases carried by organisms such as mosquitoes and ticks - in the western US, although these illnesses did not change much in other parts of the country. At the same time, El Nino conditions were associated with a lower risk of diarrhoea and intestinal illnesses in the region, but a higher risk in other parts of the country. The change seemed to be largely concentrated on tick-borne illnesses, such as Lyme disease. This is not surprising, according to Prof Fisman.
The warmer, wetter conditions El Nino tends to bring to the US West Coast can influence the larval development of insects, as well as their biting rates. They can also contribute to increased mouse populations, reservoirs for disease-carrying ticks.
The changes in intestinal disease rates were more difficult to explain. Previous studies have suggested that both unusually wet and unusually dry conditions can lead to spikes in these types of illnesses, which tend to be transmitted through contaminated water sources.
Previous research has also suggested that climate and weather changes can influence transmission of other diseases, such as pneumonia and influenza, while this study found no changes in those illnesses.
They say the important message is that climatic shifts can influence disease outbreaks even in highly developed nations.
The study reinforces that high-income nations have a vital stake in the fight against climate change. While developing countries are still likely to be much more vulnerable to global warming's overall impact, evidence heavily suggests that no part of the world will escape untouched.
Prof Fisman said: "There's this tendency to assume, 'Oh, we have sewerage systems, if we have something like Zika or chikungunya, we'll just kill all the mosquitoes. The problems are a lot bigger than that."