The best of EcoWatch, right in your inbox. Sign up for our email newsletter!
Loss of Large Wildlife Leads to Increased Disease Risk in Humans
In the Middle Ages, fleas carried by rats were responsible for spreading the Black Plague. Today in East Africa, they remain important vectors of plague and many other diseases, including Bartonellosis, a potentially dangerous human pathogen.
Research by Hillary Young, assistant professor in UC Santa Barbara’s Department of Ecology, Evolution and Marine Biology, directly links large wildlife decline to an increased risk of human disease via changes in rodent populations. The findings appear Monday in the Proceedings of the National Academy of Sciences Early Online Edition.
With an East African savanna ecosystem as their research site, Young and her colleagues examined the relationship between the loss of large wildlife—defaunation—and the risk of human disease. In this case, they analyzed Bartonellosis, a group of bacterial pathogens which can cause endocarditis, spleen and liver damage and memory loss.
“We were able to demonstrate that declines in large wildlife can cause an increase in the risk for diseases that are spread between animals and humans,” said Young. “This spike in disease risk results from explosions in the number of rodents that benefit from the removal of the larger animals.”
The researchers discovered this effect by using powerful electric fences to experimentally exclude large species like elephants, giraffe and zebra from study plots in Kenya. Inside these plots, rodents doubled in number. More rodents meant more fleas, and genetic screens of these fleas revealed that they carried significantly numbers of disease-causing pathogens.
The study was concentrated in an area where rodent-borne disease is common and sometimes fatal. According to Young, these rodent outbreaks and associated increases in disease risk may be exacerbating health problems in parts of Africa where diminishing wildlife populations are rife.
“This same effect, however, can occur almost anywhere there are large wildlife declines,” Young said. “This phenomena that we call rodentation—the proliferation of rodents triggered by large wildlife loss—has been observed in sites around the world.”
Downturns in wildlife numbers can cause rodent increases in a variety of ways, including by providing more access to food and better shelter. “The result is that we expect that the loss of large animals may lead to a general increase in human risk of rodent borne disease in a wide range of landscapes,” Young said.
“In this study, we show the causal relationship between disturbance and disease is alarmingly straightforward,” Young added. “We knock out the large members of ecosystems, and the small species, which generally interact more closely with humans, dramatically increase in number, ultimately brewing up more disease among their ranks.
The study provides ecosystem managers with yet another reason to protect large and at-risk wildlife species. “Elephants are an irreplaceable part of our global biodiversity portfolio,” Young said, “but they also appear to be circuitously protecting us from disease.”
Also involved in the study was Douglas J. McCauley, assistant professor in the Department of Ecology, Evolution and Marine Biology at UC Santa Barbara. Other participants were Rodolfo Dirzo of Stanford University; Kristofer M. Helgen of the National Museum of Natural History, Smithsonian Institution; Sarah A. Billeter, Michael Y. Kosoy and Lynn M. Osikowicz of the Division of Vector-Borne Infectious Diseases, National Center for Infectious Diseases, Centers for Disease Control and Prevention; Daniel J Salkeld of Colorado State University, Fort Collins, and the Woods Institute for the Environment at Stanford University; Truman P. Young of UC Davis; and Katharina Dittmar of the University at Buffalo, The State University of New York.
YOU ALSO MIGHT LIKE
EcoWatch Daily Newsletter
Oil rigs around the world keep pulling crude oil out of the ground, but the global pandemic has sent shockwaves into the market. The supply is up, but demand has plummeted now that industry has ground to a halt, highways are empty, and airplanes are parked in hangars.
Under an agreement negotiated by community groups — represented by NRDC and the Pennsylvania Utility Law Project — the Pittsburgh Water and Sewer Authority (PWSA) will remove thousands of lead water pipes by 2026 in order to address the chronically high lead levels in the city's drinking water and protect residents' health.
By Dave Cooke
So, they finally went and did it — the Trump administration just finalized a rule to undo requirements on manufacturers to improve fuel economy and reduce greenhouse gas emissions from new passenger cars and trucks. Even with the economy at the brink of a recession, they went forward with a policy they know is bad for consumers — their own analysis shows that American drivers are going to spend hundreds of dollars more in fuel as a result of this stupid policy — but they went ahead and did it anyway.
By Richard Connor
A blood test that screens for more than 50 types of cancer could help doctors treat patients at an earlier stage than previously possible, a new study shows. The method was used to screen for more than 50 types of cancer — including particularly deadly variants such as pancreatic, ovarian, bowel and brain.
Preliminary data from the Centers for Disease Control showed a larger number of young people coming down with COVID-19 than first expected, with patients under the age of 45 comprising more than a third of all cases, and one in five of those patients requiring hospitalization. That also tends to be the group most likely to use e-cigarettes.