Elkhorn coral infected with white pox.
What’s the News: Over the past decade, diseases, pollution, and warming waters have put coral populations across the globe in a dramatic decline. In an extreme case, the population of elkhorn coral, considered one of the most important reef-building corals in the Caribbean, has decreased by 90–95 percent since 1980, partly due to a disease called white pox.
Now, scientists have traced this lethal disease back to humans. Human feces, which seep into the Florida Keys and the Caribbean from leaky septic tanks, transmit a white pox-causing bacterium to elkhorn coral, researchers report in the journal PLoS ONE. “It is the first time ever that a human disease has been shown to kill an invertebrate,” ecologist James Porter told Livescience. “This is unusual because we humans usually get disease from wildlife, and this is the other way around.”
What’s the Context:
- Serratia marcescens is a bacterium found in the intestines of humans and many other animals. Resistant to many types of antibiotics, S. marcescens is known to cause respiratory problems and urinary tract infections in people.
- The bacteria can also infect coral—in 2002, Porter and his colleagues learned that S. marcescens causes white pox disease in elkhorn coral. The contagious disease kills coral tissue, exposing patches of its white skeleton beneath. The researchers originally suspected that the S. marcescens infecting elkhorn coral came from human feces, but they lacked the scientific evidence needed to prove it.
- White pox is but one of over 18 diseases threatening coral. Scientists have identified only a handful of the diseases’ sources (via Livescience).
How the Heck:
- The researchers spent years gathering samples of S. marcescens from elkhorn coral, from wastewater collected from a treatment plant in Key West, and from other animals, such as the coral-eating snail Coralliophila abbreviate.
- The team then exposed healthy elkhorn coral fragments to the various bacteria samples they collected. The fragments exposed to S. marcescens from wastewater or from other, already-infected elkhorn corals began showing signs of white pox within as little as four days.
- The research also suggests that the corallivorous snail and another type of coral, Siderastrea siderea, may play a role in spreading white pox. One of the coral fragments infected with S. marcescens from the snail developed signs of the disease within 13 days, while S. marcescens isolated from the other coral species caused white pox in 20 days.
The Future Holds: In 2001, Key West installed an advanced wastewater treatment system capable of reducing the bacterium to undetectable levels, and has not had a new case of white pox since, the researchers told ScienceNOW. They hope that the new study will encourage communities throughout the Caribbean to upgrade their wastewater management facilities, too.
Image courtesy of James W. Porter/University of Georgia