Algae virus leaves DNA footprints in human throats

The discovery is no cause for alarm, said Dr. Robert H. Yolken, a virus expert at the Johns Hopkins Children's Center, but it's certainly odd: A bug known before only to infect green algae appears to have jumped from the plant to the animal kingdom, landing in the human throat.

Without infecting people, this bug, or at least its DNA footprint, appears to make trouble, although not so much that the 40 healthy people who turned out to be harboring it noticed anything amiss. It took a test to find an effect in humans, then to corroborate the results in mice, ultimately linking the algae virus traces to slightly diminished mental functions, including attention, spatial orientation and memory.

Published last month online in the Proceedings of the National Academy of Sciences, the research by Yolken and 17 co-authors is another drop in a growing sea of information on the microorganisms living in our bodies and how they may affect us. The microbiome, as it's called, contains roughly 10,000 species of organisms and consists of about 10 times as many cells as the human body. Taken together, their collective weight is put at up to three pounds, equal to a human brain.

Elements of this vastly complicated entity that has been viewed as another body organ, or even another genome, have been identified as suspected risk factors in several conditions, including obesity, autism, depression and schizophrenia.

"We don't want to scare anyone," Yolken said.

Humans evolved alongside the organisms that make up the microbiome, he explained, and, for the most part, have developed a healthy working relationship with them. While this is the first time that traces of the algae virus have been found in people's throats there was an earlier report of this virus' DNA showing up in a vaginal sample the virus has not been found intact in people, or to be replicating itself in human cells or infecting anyone.

Plant viruses have been known to replicate themselves in insects, but not in animals, said James L. Van Etten, a professor of plant pathology at the University of Nebraska, and a co-author of the recent research report. Such a discovery would be exciting, he said, but "I think it's highly unlikely."

The research, however, does suggest a link between a virus and brain function. That possible connection is a specialty for Yolken, who directs the Stanley Division of Developmental Neurovirology at Johns Hopkins Hospital.

Their examination some years ago of brain tissue samples turned up traces of DNA that they did not immediately recognize. A search led Yolken and his researchers to a bug called chlorovirus ATCV-1, known only to infect green algae. That led them to Van Etten, an authority on this virus.

Van Etten recalled receiving an email from Yolken on a Sunday, and thinking someone was kidding.

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Algae virus leaves DNA footprints in human throats