Spherule and endospore forms of Coccidioides immitis. Credit: CDC/Dr. Edwin P. Ewing, Jr.
Last summer, three patients in the United States acquired malaria without leaving their home states of Florida, Texas and Maryland. Before this, locally acquired mosquito-borne malaria had not occurred in the U.S. since 2003.
So, what changed in the 20 years from 2003 to 2023 to cause such an incident? The climate, for one.
Climate change is happening now. Nine of the 10 hottest years on record have occurred in the past decade and were accompanied by extreme heat waves, droughts, wildfires, hurricanes, and severe flooding. And a change in weather patterns means a change in the infectious disease landscape, according to a team of infectious disease experts from Massachusetts and California.
In a new article published in JAMA, the experts warn that climate change will fuel the spread of infectious diseases. They call for more awareness and preparedness in the medical field, urging the community to update their education and training and take steps to combat global warming.
“Clinicians need to be ready to deal with the changes in the infectious disease landscape,” said lead author George Thompson, professor at the UC Davis School of Medicine. “Learning about the connection between climate change and disease behavior can help guide diagnoses, treatment and prevention of infectious diseases.”
For example, malaria-spreading mosquitoes are expanding northward, a climate-induced alteration. And the same is true for other vectors bearing disease, like dengue, Zika and Lyme disease.
As the winters become warmer and shorter and the summers before hotter and longer, vectors have been able to adapt—expanding their range, elongating their active periods and driving up the disease transmission rate.
“We're seeing cases of tick-borne diseases in January and February. The tick season is starting earlier and with more active ticks in a wider range. This means that the number of tick bites is going up and with it, the tick-borne diseases,” said first author Matthew Phillips, an infectious diseases fellow at Massachusetts General Hospital and Harvard Medical School.
The study also pointed to the emergence of new fungal infections, such as Candida auris, and changes in the location of some fungal pathogens. For example, the fungal infection Coccidioides (also known as Valley fever) was endemic to hot, dry areas in California and Arizona. But, Valley fever was recently diagnosed as far north as Washington State.
The researchers say rising sea levels along with an increased frequency of storm surges and coastal flooding can also affect the spread of waterborne diseases, such as E. coli and Vibrio.
Lastly, zoonotic diseases, such as plague and hantavirus (carried by rodents), are showing changes in incidence and location. Due to habitat loss, animal migration patterns are changing and wild animals are coming into closer proximity to humans than ever before. This brings a higher risk of animal diseases spilling over to humans, creating another avenue for new pathogens to develop and old ones to spread.
SARS-CoV-2, the last pathogen to lead to a global pandemic, was a zoonotic disease.
“They can spring up and cause absolute chaos for the whole world and then we kind of forget about them for a while. Yet, the epidemic and pandemic potential of infections really mandates that we stay involved with federal funding agencies and advisory groups to make sure that infectious diseases don't slip back too far on the public's radar,” said Thomspon.
Thompson, Phillips and the rest of the team have called for stronger measures for infectious disease surveillance and are urging medical educators to train clinicians to anticipate the changes in infectious disease patterns.
“It's not a hopeless situation,” said Phillips. “There are distinct steps that we can take to prepare for and help deal with these changes. Clinicians see first-hand the impact of climate change on people’s health. As such, they have a role in advocating for policies that can slow climate change.”