Current evidence suggests that many organisms will struggle to keep up with Earth's changing climate. Unfortunately for humans, however, some pathogens are not only adapting to climate change but also thriving, as this new study shows, including the bacteria that cause the common diarrheal disease campylobacteriosis.
The culprit behind this debilitating zoonotic disease is bacteria of the genus Campylobacter. While there are 17 species and 6 subspecies of Campylobacter, the most common ones that cause illness in humans are Campylobacter jejuni and Campylobacter coli, which are often transmitted to us from animal products.
British scientists studied how rising temperatures, longer daylight hours and increased humidity - all side effects of Earth's current climate change - affect the spread of Campylobacter and found that the disease has a strong link to a warming planet.
Giovanni Lo Iacono, senior lecturer in biostatistics and epidemiology at the University of Surrey, said: "This information is extremely valuable because diseases such as campylobacteriosis not only cause discomfort to individuals but also have a huge social impact, with people having to take sick leave and putting additional pressure on health services around the world."
The researchers analyzed data from the UK Health Security Agency (UKHSA), which included around 1 million cases of campylobacteriosis in England and Wales over 20 years. Using a mathematical model that took comparative weather data into account, the team found a clear link between disease and climate.
Cases remain stable when temperatures are below 8°C (46°F) and steadily increase with every 5°C (9°F) temperature rise. Infections also surge when humidity is between 75% and 80%. Finally, longer daylight hours (sunlight for more than 10 hours) again showed higher infection rates, and when this was associated with higher humidity, infection rates were even higher. However, they found no link between the disease and the variables of rain or wind.
"We found that warmer temperatures, increased humidity and longer day lengths are associated with the spread of campylobacteriosis," said LoIacono. "We don't fully understand why this is. It could be that warmer weather increases the survival and spread of pathogenic bacteria (and therefore the weather that causes disease), or it could be people's behavior and how they socialize during this period." "What we do know, however, is that climate change not only impacts the environment, but may also negatively impact our health by fueling the spread of infectious diseases," he added.
According to the World Health Organization, about one in 10 people worldwide is now infected with campylobacteriosis each year, and it is one of the leading causes of diarrheal disease. Campylobacteriosis is most commonly spread through undercooked poultry, other meats and meat products, and contaminated (or undercooked) milk, water, and ice. Symptoms such as diarrhea, abdominal pain, headache, nausea, vomiting and fever usually last three to six days, but may last up to 10 days. More bacteria are able to thrive in the changing environment, increasing the risk of foodborne illnesses like campylobacteriosis.
Gordon Nicholls, Visiting Professor at the University of Surrey, said: "Environmental data can help us understand the complex patterns of disease transmission. Having this knowledge is invaluable as it can help us identify areas that are vulnerable to potential outbreaks and ensure that resources are available in these areas to treat affected people and contain the spread of the disease to other areas."
The bad news is that while researchers have identified a link between climate change and the prevalence of campylobacteriosis, they are not entirely sure of the mechanisms behind it. This is their next research direction.
"It has been widely accepted since Hippocrates that weather and climate influence the spread of disease," LoIacono said. "Unraveling why this is, and what specific environmental factors drive the spread of disease, is a complex problem and not yet fully understood. Now that we have a detailed description of how weather affects disease, the next step is to understand why. Importantly, with our transparent and conceptually simple approach, we can now determine the risk of contracting a disease given the local recent weather."
The research was published in the journal PLOS Computational Biology.