Climate change is linked to more floods, hotter and drier weather, and melting sea ice, but it could also affect infectious diseases like Lyme disease and West Nile Virus. The problem is we don't know how.
The National Climate Assessment was released this week. The part about Connecticut and the northeast deals with the spread of infectious diseases, like Lyme disease and West Nile virus. One paragraph points to a possible link between more rain in the late spring and early summer, and more cases of Lyme disease. It projects Lyme disease migrating slowly towards the north.
The assessment also says the northeast could be more susceptible to mosquitoes that carry the West Nile virus. That means more than 30 million people in the area could be exposed to these mosquitoes by the end of the century.
The maps below show the projected spread of ticks that transmit Lyme disease. Red means the places are more likely to become established tick habitats:
Credit: Alan Yu for WNPR. Maps from John S. Brownstein and Theodore R. Holford / Durland Fish/National Climate Assessment
The problem is that the information is rather speculative, said Durland Fish, a professor of epidemiology at the Yale School of Public Health. He also served on a panel reviewing the National Climate Assessment.
Fish said we need a lot more research that can draw on when trying to figure out how climate change can affect infectious diseases like West Nile virus or Lyme disease. "It's really a neglected area," he said. "I'm serious when I say we're decades behind. When you look at all the work that's been done with agriculture, and ecology, and forestry, and things like that, they have decades of experimental data to make intelligent predictions about climate change in their particular fields. We don't have that luxury in infectious diseases, because the research has not been done."
There is a lot more research in environmental health, Fish said, such as allergens and air pollution. That is the kind of research that needs to be funded for infectious disease. As an example, he pointed to one of several articles cited in the report showing a longer ragweed pollen season in central North America.
"That’s a nice study," Fish said. "More [carbon dioxide], more ragweed pollen; good evidence. But I can’t point to a single study like that on a tick-borne disease or a mosquito-borne disease. I can’t point to a study that would be that experimental, [or] have that kind of predictive value."
Fish said there is more of this work done in Europe because the agencies that fund research there have a broader approach when investigating infectious disease, rather than focusing on vaccines, diagnostics or therapeutics. He cited one study showing that a mosquito that spreads the chikungunya virus, which has no vaccine or treatment and was found in the Americas for the first time last year, is adapting to a warmer climate.
It's not quite so dire, said Sam Scheiner, a program director at the National Science Foundation. His program funds research on the factors that influence the spread of infectious diseases, including climate.
Scheiner said it is important to know how climate change affects diseases -- and it is being studied. He mentioned research that found a kind of bacteria that spreads cholera more quickly when the water in the Gulf of Mexico was warmer. Health officials can use the research to give out better-timed warnings not to swim in certain areas. Researchers can also factor information into climate change models to forecast how the incidence of cholera may grow, depending on how the Gulf warms.
Scheiner said there isn't a huge lack of research and funding. Rather, the processes are complex. "We can say, yes there are going to be changes," he said. "In some cases, we can say there's a good likelihood that disease incidence will increase. We also know, though, that if we can anticipate these changes, it is possible to mitigate the harm."