Parkinson’s disease Lactococcus gut bacteria
© STEVE GSCHMEISSNER/SCIENCE PHOTO LIBRARY
People with Parkinson’s seem to have less Lactococcus bacteria in their gut
Parkinson's disease could be triggered by a virus that kills a "good" form of bacteria in the gut. This may lead to a chain reaction of damaged nerves leading from the digestive system up to the brain.

Parkinson's disease is a progressive disorder of tremors, stiffness and difficulties in moving; it is known to involve the death of nerve cells in the brain, linked with misfolding of a protein found in nerve fibres called synuclein.

Although it has long been seen as a brain disorder, a recent theory is that the misfolding of synuclein starts in nerves of the gut, triggering a chain reaction of protein misfolding up the nerve fibres to the brain . But it's unclear what starts the changes to synuclein in the first place.

George Tetz of the Human Microbiology Institute in New York thinks gut microbes might be responsible. After analysing existing data on the gut microbes of 31 people with Parkinson's disease and 28 healthy people, his team found that the biggest differences were in the dairy bacteria such as Lactococcus species, and the viruses that prey on them.

Low levels

The viruses, called bacteriophages, invade the bacteria, reproduce inside them and then burst out, killing them. So it's unsurprising that higher levels of the virus would lead to lower Lactococcus levels, says Tetz.

People with Parkinson's disease had twice the levels of harmful forms of the virus and just one tenth the level of Lactococcus. "Most likely this is more than a coincidence," says Tetz.

The differences could not have been caused by Parkinson's medication as the patients had all been recently diagnosed and had not yet started treatment.

The finding is hardly clear-cut. For example, last year another group looked at the same microbiome data using a different analysis technique; they found differences in other species but not in Lactococcus.

And it's unclear whether microbial changes cause the nerve damage that leads to Parkinson's or are a consequence of it.

If the loss of Lactococcus does turn out to play a role in causing Parkinson's, consuming more dairy products might not help - because these may contain the Lactococcus-killing virus as well as the bacteria. And by the time people are diagnosed with Parkinson's, it might be too late to stop the protein chain reaction anyway, says Tetz.

The findings were presented at the American Society for Microbiology Microbe conference in Atlanta last week.