Contaminated water is the leading cause of large-scale outbreaks of infectious diseases that can be transmitted from animals to people, researchers say.
These health threats are called zoonotic infectious diseases, and recent outbreaks include COVID-19 and Ebola.
"In the age of COVID-19, it is understandable that many people may not realize how many outbreaks of other infectious diseases are caused by complex, intertwined ecological and socioeconomic conditions," said lead author Patrick Stephens, an associate research professor at the University of Georgia's Odum School of Ecology in Athens.
His team analyzed 4,400 zoonotic disease outbreaks worldwide since 1974. They identified the 100 largest, all of which infected thousands to hundreds of thousands of people. These were compared with 200 outbreaks that included 43 or fewer cases.
Water contamination was the most common cause of large outbreaks and the second most common cause of smaller ones. Examples of these water-associated diseases include hepatitis E, typhoid and dysentery.
In addition to water contamination, large outbreaks were most often caused by unusual weather patterns, changes in the abundance of disease carriers such as mosquitoes and ticks, and sewage management.
Large outbreaks were also much more likely to be caused by viral pathogens such as SARS coronavirus, influenza virus and Japanese encephalitis virus. Smaller outbreaks were associated with food contamination, local livestock production and human-animal contact.
The researchers also found that large outbreaks tended to be caused by a greater variety of factors than small outbreaks, according to findings recently published in the journal Philosophical Transactions B.
"We know that factors like exposure to wild mammals, habitat disruption, international trade and travel and contact with contaminated food and water are important considerations," Stephens said in a university news release. "Our research was designed to understand what proportion of outbreaks various drivers contributed to. To our knowledge, this study is the first to do so for a global sample of outbreaks of many diseases."
Stephens said much work remains to understand how large-scale infectious disease outbreaks can be prevented and controlled.
"Perhaps two-thirds of future infectious disease outbreaks are expected to be caused by zoonotic pathogens, and the number of these diseases is growing worldwide," he said. "Our research is an extremely important first step to better understand global variation in the drivers of outbreaks."
The U.S. Centers for Disease Control and Prevention has more on zoonotic diseases.
SOURCES: University of Georgia, news release, Oct. 26, 2021