Under the Category of Another Thing to Worry About: Algal Virus Infects, Affects Humans

The human body is host to trillions of microbes. These microbes significantly outnumber the body's cells. Although most are beneficial to human health, some of these microbes can cause problems. Research in both humans and animal models has shown that microbial communities can affect many biological functions, including cognitive performance.

An alga species infected with a chlorovirus (red) similar to the one the researchers identified in the throat cavity of humans. Credit: Kit Lee and Angie Fox, University of Nebraska-Lincoln.

Most studies of microbial communities and their genes, collectively known as the microbiome, have focused on bacterial and fungal communities. DNA is extracted from samples, and then specific regions that are universal to bacteria or fungi are analyzed to distinguish the microbes. The viral components of the microbiome (the virome) have received less attention, largely because viruses are so diverse that there are no universal viral target regions. Recent advances, however, have made whole-genome sequencing faster and less expensive. Thus scientists can now sequence entire viral genomes.

A group led by Dr. Robert Yolken at Johns Hopkins University has been studying the links between viral infections and brain development. They were analyzing viruses taken from the throats of 33 healthy adults who were participating in a study that involved the assessment of cognitive functioning. Unexpectedly, the researchers discovered genetic sequences from Acanthocystis turfacea chlorella virus 1 (ATCV-1). ATCV-1 is a type of Chlorovirus, which infects green algae. These viruses are common in fresh water, such as lakes and ponds, but weren't thought to infect humans or animals.

To further investigate, the group teamed with Dr. James Van Etten, an expert on algal viruses at the University of Nebraska-Lincoln. Their work was supported in part by NIH’s National Institute of Mental Health (NIMH) and National Center for Research Resources (NCRR). Results appeared online on October 27, 2014, in Proceedings of the National Academy of Sciences.

A sequence-specific assay detected ATCV-1 in throat samples from 40 of 92 (44%) people in the study. The team next examined the link between ATCV-1 and performance on a battery of cognitive tests. ATCV-1 was associated with decreases on tests of visual processing. There was no difference on tests of general knowledge.

Studies in people can involve many complex factors, so the scientists infected a group of mice with ATCV-1. The exposed mice performed worse than control mice in several cognitive tests, such as navigating mazes. The researchers next studied gene expression in the hippocampus, a brain region essential for learning, memory, and behavior. Exposure to ATCV-1 was associated with significant changes in the regulation of over 1,000 genes.

"People have conducted studies looking for more conventional viruses and bacteria in throat swabs, but the way those studies were done meant that they could have easily missed the ones that we work with," Van Etten says.

More study will be needed to learn how ATCV-1 may alter cognitive functioning. If confirmed, these findings hint that other yet-unknown viruses may have subtle effects on human health and behavior.

—by Harrison Wein, Ph.D.

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Under the Category of Another Thing to Worry About: Algal Virus Infects, Affects Humans

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