BREATHING in a bit of dirt might be enough to give you Parkinson鈥檚. According
to a new theory, rare strains of a common soil bacterium may trigger the
disease.
The bacterium Nocardia asteroides is known to cause a lung infection
in humans that sometimes leads to brain abscesses. So microbiologist Blaine
Beaman from the University of California, Davis, injected disease-causing
strains of the bacterium into mice to find out how. Some of the mice developed
the lung and brain symptoms, but hundreds of others became shaky and slow in
their movement鈥攕ymptoms that looked like Parkinson鈥檚.
Electron microscopy revealed that the bacteria travelled to a small part of
the brain鈥檚 basal ganglia that is involved with control of movement. There they
infected neurons that make dopamine鈥攖he same brain cells that are attacked
in Parkinson鈥檚. The bugs also left clumps of proteins within brain cells,
suspiciously like the Lewy bodies that are characteristic of Parkinson鈥檚 and
some dementias.
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This suggests that particular strains of the bacterium may be triggering
Parkinson鈥檚, Beaman told a meeting of the Society for General Microbiology at
the University of East Anglia this week.
Nocardia can be found in almost any soil sample, he says. 鈥淲e鈥檙e all
breathing it, we鈥檙e all dealing with it on a daily basis,鈥� he says. But only a
few of the thousands of strains are likely to produce any symptoms.
鈥淲e know that infection has caused Parkinson鈥檚-like diseases in the past,鈥�
says Adrian Williams, a neurologist at the University of Birmingham, 鈥渟o it鈥檚
possible.鈥� These outbreaks followed epidemics of flu or sleeping sickness. He
says that while bacterial infections aren鈥檛 the most likely cause of
Parkinson鈥檚, they could be the trigger in some cases.
But proving the link will be tricky. Beaman says that once the mice began
showing the Parkinson鈥檚-like symptoms, the bacteria mysteriously disappeared
from their brains. So autopsies of human brains might not reveal any bacteria,
even if they were to blame. Beaman is now working with Peter LeWitt at Wayne
State University in Detroit to see if the bacteria left behind any DNA traces.
鈥淲e鈥檝e got some really interesting results, but it鈥檚 premature to discuss,鈥� he
says.
No one has correlated Nocardia infections with Parkinson鈥檚 before,
but Beaman notes that both are on the rise and are most likely to strike elderly
men. Any relationship might also be hard to spot because a bacterium confined to
the brain is unlikely to be very contagious.
Beaman and LeWitt both say that most researchers don鈥檛 believe Parkinson鈥檚 is
infectious. 鈥淚t is sort of a heretic view,鈥� says LeWitt. 鈥淏ut similar resistance
came up against a bacterial cause of ulcers.鈥�
Beaman hopes that establishing the link will point the way to new treatments
for Parkinson鈥檚. But while antibiotics are a successful treatment for the lung
disease caused by Nocardia, they don鈥檛 work on mice or humans whose
brains are infected. And LeWitt says it probably won鈥檛 be possible to make a
vaccine, since the tiny number of bacteria involved doesn鈥檛 seem to trigger an
immune response. 鈥淗aving antibodies doesn鈥檛 necessarily protect you,鈥� he says.