(CN) — Scientists have identified a disturbing trend in which climate change can worsen the severity and regularity of infectious diseases in livestock, which in turn can exacerbate climate change in a kind of vicious cycle.
The study, published Wednesday in the journal Trends in Ecology & Evolution, was led by Vanessa Ezenwa, a professor of ecology at the University of Georgia, where she and her team found that parasitic infections in livestock animals can result in increased methane output.
Climate conditions have long been affecting how diseases are spread. For example, flu season comes around in the winter because the conditions allow it to spread more, as cold air allows the virus to remain in the air longer. Studies show that zoonotic diseases are highly affected by climate variability, leading the authors of this study to wonder how this factored into livestock methane production.
"There is evidence that climate change, and warming temperatures in particular, are impacting some infectious diseases and increasing their prevalence," Ezenwa said. "If that's happening for livestock diseases, and simultaneously higher prevalence is triggering increased methane release, you could end up with what we call a vicious cycle."
Cattle are the leading agricultural contributors to greenhouse gas emissions, responsible for 14.5% of emissions worldwide as of 2019. Cows can eat more than 20% a day, and as they do this they burp and release methane gas, which although shorter lived than carbon dioxide, it is 28 times more harmful in warming the atmosphere.
For this reason, many health officials and scientists have encouraged people to cut back on their meat consumption until more eco-friendly, sustainable practices are developed. Scientists have been testing high-fiber diets as a way to limit methane outputs and limit the amount of rangeland needed.
A part of this study involved a target research group led by senior scientist in biology in arts & sciences at Washington University, Amanda Koltz, designated to investigate the role parasitic diseases have to play in this cycle. The team, consisting of ecologists, veterinarians and One Health experts studying zoonotic diseases, reviewed several studies pertaining to livestock health.
"Infectious diseases impact all animals, but our understanding of how their effects extend to the broader ecosystem is still limited," Koltz said. "For example, parasite-host interactions can shape host physiology, behavior and population dynamics — some of those impacts are likely to have widespread, cascading effects on ecosystem-level processes."
The researchers were particularly interested in cows, sheep, and goats. Not only are these animals in high demand in the meat and dairy industry, but they are what is known as ruminant livestock, meaning they get their nutrients from plant-based food and heavily depend on their environment for sustenance. They are also highly affected by parasites and diseases.
In one study, they found that sheep who had intestinal worms produced 33% more methane per kilogram of feed than healthy individuals. The worms also inhibited the sheep’s growth and as a result, they produced more methane before they were ready to be slaughtered.
Another study looked at dairy cattle infected with mastitis, a common disease in which a bacterial infection in the udder causes abnormalities in milk. In these animals, cows with mastitis produced 8% more methane per kilogram of milk than healthy individuals.
Based on this, the team concluded that parasites and infectious diseases cause livestock to contribute significant amounts of methane. According to the Food and Agriculture Organization of the United Nations, livestock production worldwide is predicted to increase every year by 2.7%, and in turn the methane production that follows will spike by 20% from 2017 to 2050. However, after the results of this study are factored in, parasitic infections in livestock could more than double the methane emissions, resulting in an astonishing 82%.
"With human consumption of meat increasing four- to five-fold since the 1960s along with the ever-increasing impacts from climate change, this vicious climate-disease cycle is one more example of the interconnection of our greatest planetary ills — climate change and emerging infectious diseases," said co-author Sharon Deem, the director of the Saint Louis Zoo Institute for Conservation Medicine.
Needless to say, the authors hope that their paper urges experts and officials to pay close attention to methane emissions and to take parasitic infections into consideration when calculating climate risks.
"The vicious cycle between climate impacts on disease and disease impacts on climate is striking," said co-author Aimée Classen, a professor of ecology and evolutionary biology and director of the University of Michigan Biological Station. "Our study highlights that scientists need to incorporate both animals and disease into the experiments and models used to predict future carbon emissions."
Read the Top 8
Sign up for the Top 8, a roundup of the day's top stories delivered directly to your inbox Monday through Friday.