White Plague Decimating Corals May Be Viral, Not Bacterial

Brett Smith for redOrbit.com – Your Universe Online

Just as the black plague laid waste to communities across Medieval Europe, a ‘white plague’ has been decimating marine corals in the Caribbean.

Once thought to be caused mainly by bacteria, researchers at Oregon State University have found that a group of small, circular, single-strand DNA (SCSD) viruses are connected to the dramatic rise of white plague that has occurred in recent decades.

The Oregon researchers said they are racing to learn more about the disease and how to prevent it because of its widespread, debilitating impact on coral reef health in the Caribbean.

“Twenty years ago you had to look pretty hard to find any occurrences of this disease, and now it’s everywhere,” said study author Nitzan Soffer, a doctoral student in the Department of Microbiology at OSU. “It moves fast and can wipe out a small coral colony in a few days.”

“In recent years the white plague has killed 70-80 percent of some coral reefs,” Soffer said. “There are 20 or more unknown pathogens that affect corals and in the past we’ve too-often overlooked the role of viruses, which sometimes can spread very fast.”

In the study, which was recently published in the Multidisciplinary Journal of Microbial Ecology, the scientists used transmission electron microscopy and genetic sequencing techniques to compare 24 genomes of viruses found in Caribbean corals that had exhibited symptoms of disease.

While the researchers found SCSD viruses in some of the diseased tissue samples, they were unable to find these viruses in healthy corals.

According to the OSU team, marine wildlife diseases are becoming increasingly prevalent. They cited reports of non-bleaching coral disease that have increased more than 50-fold since 1965. These diseases are contributing to declines in coral abundance and cover, the scientists added.

White plague is one of the most aggressive coral diseases, causing rapid tissue loss, affecting a wide range of corals and potentially causing partial or total colony collapse. While some bacteria have been associated with the disease, the OSU study indicates that viruses also play a role, perhaps a central one.

The researchers also found that corals with white plague disease had higher viral diversity than their healthier counterparts.

Marine biologists have been emphasizing that rising ocean temperatures that could result from global warming would stress corals and make them more susceptible to disease. The OSU team said temperature may be another factor behind the recent rise of white plague because the disease frequently appears to be at its height near the end of summer.

Overfishing allows more algae to grow on corals and could be helping to spread disease, researchers said. They added that pollution from sewage outflows in some marine habitats may also be compromising coral health.

The researchers concluded by pointing out that viral infection alone does not automatically cause major problems and disease. Many healthy corals can become infected with herpes-like viruses that persist in their system but are not fatal. These symptoms-free viruses are frequently found in other vertebrate hosts, including humans.