What data did you use to demonstrate a link between parasites and extreme weather?
Since the early 90s, the Colorado Department of Public Health and Environment has been systematically collecting data on two parasitic diseases that impact public health: cryptosporidiosis and giardiasis. Using this data and data from the National Center for Atmospheric Research, we were able develop models to examine how weather variables impact the case reports. From there, we determined the time period between when people are likely exposed to certain weather conditions and when they are detected in the system as reported health cases.
What did the analysis show?
This analysis showed the time lag between the weather conditions and reporting of illness is much longer than we expected. Our analyses provided evidence that the lagged effects of extreme weather on case reports could at times be as long as a year. We saw the risk of cryptosporidiosis increased with higher temperatures. Surprisingly, we found that this pattern didn't apply to giardiasis. Instead, we observed an increased risk of giardiasis with lower temperatures. This highlights significant differences between these two parasites, despite their similar life cycles and dependencies on the environment. Extreme temperatures can affect each parasite in opposite ways, illustrating their distinct responses to environmental conditions.
Are waterborne illnesses a big public health concern here in Colorado?
Yes. Cryptosporidiosis became a major focus because it is very hard to kill with typical disinfectants. It caused major outbreaks in water parks in the 1990s, which is when it became a reportable disease. It causes significant gastrointestinal symptoms, such as diarrhea, fever and vomiting, which usually resolve on their own. However, higher-risk individuals can develop severe, long-term infections that can lead to chronic health issues and organ stress. Even healthy individuals can experience severe cases. It’s also a public health concern due to its ease of transmission between animals and humans.
What actions should be taken from a public health perspective now?
I debated whether this study would interest the general public because it's not about immediate actions, like avoiding water when it’s hot. Instead, we observed long lag periods, where increased transmission occurs months after high temperatures. This indicates that the connections exist, and as climate change progresses with more extreme weather, we need to understand what to be on the lookout for. From a researcher's perspective, it's valuable to understand this, but it's also important to avoid causing unnecessary fear. We're highlighting a nuanced and complex relationship here, not a simple cause-and-effect scenario based solely on temperature.
Ideally, we'd develop surveillance systems from studies like these to predict peak times and give us advanced warning. But we haven't yet sorted out how to detect problems early enough to provide early warnings. The experience with COVID-19 has shown that accurate prediction and response systems are possible, and similar models could be applied to waterborne diseases and other weather-related health issues in the future.
With weather extremes increasing, what do you expect to see?
This study touches on the impact of independent temperature and precipitation events, but there's also the issue of these factors combining. For example, a hot drought period followed by heavy rainfall can cause significant ecosystem shifts and spillover events. This might explain the long lag periods we observed. While this study didn't look at the combination of events, weather extremes often act together. When the right conditions align, they can trigger major outbreaks.
Now that you’ve established this link, what do you plan to study next?
One thing we’re interested in looking at next is the potential role of hosts that commonly pass the parasites to people. Both cryptosporidiosis and giardiasis can pass between humans and other animals, but we think livestock might play a larger role in cryptosporidiosis transmission. For instance, heavy rainfall near livestock areas can wash the parasite into water sources, leading to human contact. For giardiasis, we'd like to investigate which species are most prominent. In Colorado, we don’t know the exact sources, but we've considered possibilities like dog parks.
This research highlights that something significant is happening, and we’d love to dive deeper to find out what exactly could be at the root of it.
